COVER PHOTO
Courtesy of Edwin Adilson Rodriguez, Federal Transit Administration
DISCLAIMER
This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of
information exchange. The United States Government assumes no liability for its contents or use thereof. The United States
Government does not endorse products or manufacturers. Trade or manufacturers’ names appear herein solely because
they are considered essential to the objective of this report.
ii
Transit Noise and
Vibration Impact
Assessment Manual
SEPTEMBER 2018
FTA Report No. 0123
PREPARED BY
Antoinette Quagliata
Federal Transit Administration
Office of Planning and Environment
Meghan Ahearn
Eric Boeker
Christopher Roof
John A. Volpe National Transportation
Systems Center
Cambridge, MA 02142
Lance Meister
Herbert Singleton
Cross Spectrum Acoustics
East Longmeadow, MA 01028
Utah: Salt Lake City, UT 84102
SPONSORED BY
Federal Transit Administration
Office of Planning and Environment
U.S. Department of Transportation
1200 New Jersey Avenue, SE
Washington, DC 20590
iii
iv
Form Approved OMB No.
0704-0188
The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data
sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other
aspect of this collection of information, including suggestions for reducing the burden, to Department of Defense, Washington Headquarters Services, Directorate for Information
Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other
provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.
PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS.
1. REPORT DATE
2. REPORT TYPE
3. DATES COVERED
September 2018
Final
4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER
Transit Noise and Vibration Impact Assessment Manual
5b. GRANT NUMBER
5c. PROGRAM ELEMENT
NUMBER
6. AUTHOR(S) 5d. PROJECT NUMBER
Quagliata, Antoinette (FTA) TF09A1
Ahearn, Meghan (VOLPE)
5e. TASK NUMBER
Boeker, Eric (VOLPE)
NLJ56
Roof, Christopher (VOLPE)
Meister, Lance (CSA)
5f. WORK UNIT NUMBER
Singleton, Herbert (CSA)
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)
8.
PERFORMING
U.S. Department of Transportation
ORGANIZATION
REPORT
Volpe National Transportation Systems Center
NUMBER
55 Broadway
FTA Report No.
0123
Cambridge, MA 02142
9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR'S
U.S. Department of Transportation ACRONYM(S)
Federal Transit Administration
FTA
Office of Planning and Environment
11.
SPONSOR/MONITOR'S
1200 New Jersey Avenue, S.E.
REPORT
NUMBER(S)
Washington, DC 20590
FTA Report No.
0123
12. DISTRIBUTION/AVAILABILITY STATEMENT
This document is available through the FTA website: http://www.fta.dot.gov/.
13. SUPPLEMENTARY NOTES
14. ABSTRACT
This report is the third edition of a guidance manual originally issued in 1995. It includes clarifications to existing policy and updates to
outdated references where applicable. Topics presented in this manual include procedures for predicting and assessing noise and
vibration impacts of proposed transit projects for different stages of project development and different levels of analysis. Additional topics
include descriptions of noise and vibration mitigation measures, construction noise and vibration, and how to present these analyses in
the Federal Transit Administration’s environmental documents. This guidance is for technical specialists who conduct the analyses, as well
as project sponsor staff, Federal agency reviewers, and members of the general public who may be affected by the projects.
15. SUBJECT TERMS
Transit noise and vibration analysis, noise and vibration impact criteria, noise and vibration mitigation measures, environmental impact
assessment, Nation Environmental Policy Act compliance.
16. SECURITY CLASSIFICATION OF:
17. 18. 19a. NAME OF RESPONSIBLE PERSON
LIMITATION NUMBER
a. REPORT b. ABSTRACT c. THIS
OF
OF
PAGES
Unclassified Unclassified
PAGE
19b. TELEPHONE NUMBER
ABSTRACT
258
Unclassified
(Include area code)
v
Table of Contents
SECTION 1: INTRODUCTION .................................................................................................. 1
1.1 P
URPOSE.................................................................................................................................................................1
1.2 O
RGANIZATION OF THE MANUAL ....................................................................................................................2
SECTION 2: PROJECT CLASS OF ACTION AND PLANNING ............................................ 3
2.1 P
ROJECT CLASS OF ACTION ...............................................................................................................................3
2.2 P
ROJECT PLANNING AND DEVELOPMENT ........................................................................................................4
2.3 M
ITIGATION POLICY CONSIDERATIONS........................................................................................................... 5
SECTION 3: TRANSIT NOISE.................................................................................................... 9
3.1 N
OISE METRICS...................................................................................................................................................10
3.2 S
OURCES OF TRANSIT VEHICLE NOISE............................................................................................................10
3.3 P
ATHS OF TRANSIT NOISE FROM SOURCE TO RECEIVER..............................................................................14
3.4 R
ECEIVER RESPONSE TO TRANSIT NOISE........................................................................................................16
SECTION 4: NOISE IMPACT ANALYSIS ............................................................................... 19
4.1 D
ETERMINE NOISE IMPACT CRITERIA..............................................................................................................20
Step 1: Identify Project Type. ..................................................................................................................................21
Step 2: Choose Land Use Category for FTA Criteria........................................................................................23
Step 3: Determine Appropriate FTA Criteria Presentation.............................................................................25
4.2 D
ETERMINE NOISE ANALYSIS LEVEL.................................................................................................................31
4.3 E
VALUATE IMPACT: NOISE SCREENING PROCEDURE ....................................................................................33
Step 1: Identify Project Type ...................................................................................................................................33
Step 2: Determine the Screening Distance.........................................................................................................33
Step 3: Identify Study Area......................................................................................................................................34
Step 4: Locate Noise-Sensitive Land Uses...........................................................................................................34
4.4 E
VALUATE IMPACT: GENERAL NOISE ASSESSMENT ........................................................................................37
Step 1: Identify Noise-Sensitive Receivers............................................................................................................38
Step 2: Determine Project Noise Source Reference Levels ............................................................................39
Step 3: Estimate Project Noise Exposure by Distance.....................................................................................48
Step 4: Combine Noise Exposure from All Sources..........................................................................................49
Step 5: Estimate Existing Noise Exposure...........................................................................................................50
Step 6: Inventory Noise Impacts ............................................................................................................................52
Step 7: Determine Noise Mitigation Needs........................................................................................................54
4.5 E
VALUATE IMPACT: DETAILED NOISE ANALYSIS ............................................................................................64
Step 1: Identify Noise-Sensitive Receivers............................................................................................................66
Step 2: Determine Project Noise Source Reference Levels ............................................................................70
Step 3: Determine Propagation Characteristics.................................................................................................84
Step 4: Combine Noise Exposure from All Sources..........................................................................................91
Step 5: Determine Existing Noise Exposure.......................................................................................................92
Step 6: Assess Noise Impact ...................................................................................................................................95
Step 7: Determine Noise Mitigation Measures .................................................................................................97
SECTION 5: TRANSIT VIBRATION...................................................................................... 109
5.1 G
ROUND-BORNE VIBRATION AND NOISE METRICS ................................................................................. 110
5.2 S
OURCES OF TRANSIT GROUND-BORNE VIBRATION AND NOISE........................................................... 112
5.3 P
ATHS OF TRANSIT GROUND-BORNE VIBRATION AND NOISE............................................................... 116
vi
5.4 R
ECEIVER FACTORS THAT INFLUENCE GROUND-BORNE VIBRATION AND NOISE............................... 117
5.5 H
UMAN RESPONSE TO TRANSIT GROUND-BORNE VIBRATION AND NOISE ......................................... 117
SECTION 6: VIBRATION IMPACT ANALYSIS ................................................................... 121
6.1 D
ETERMINE VIBRATION ANALYSIS LEVEL ..................................................................................................... 121
6.2 D
ETERMINE VIBRATION IMPACT CRITERIA................................................................................................... 123
Option A: General Vibration Assessment Criteria........................................................................................... 123
Step 1: Land Use Categories................................................................................................................................ 123
Step 2: Identify Event Frequency......................................................................................................................... 125
Step 3: Apply Impact Criteria by Land Use and Event Frequency ............................................................ 125
Option B: Vibration Impact Criteria for a Detailed Vibration Analysis ..................................................... 130
Step 1: Ground-Borne Vibration .......................................................................................................................... 130
Step 2: Ground-borne Noise................................................................................................................................. 132
6.3 E
VALUATE IMPACT: VIBRATION SCREENING PROCEDURE......................................................................... 132
Step 1: Classify project vehicles........................................................................................................................... 133
Step 2: Determine Project Type .......................................................................................................................... 134
Step 3: Determine Screening Distance ............................................................................................................. 135
Step 4: Identify Vibration-Sensitive Land Uses................................................................................................ 136
6.4 E
VALUATE IMPACT: GENERAL VIBRATION ASSESSMENT ............................................................................ 136
Step 1: Select Base Curve for Ground Surface Vibration Level .................................................................. 136
Step 2: Apply Adjustments .................................................................................................................................... 139
Step 3: Inventory of Vibration Impact................................................................................................................ 147
6.5 E
VALUATE IMPACT: DETAILED VIBRATION ANALYSIS ................................................................................ 149
Step 1: Characterize Existing Vibration Conditions ....................................................................................... 149
Step 2: Estimate Vibration Impact.............................................................................................................................. 152
Step 3: Assess Vibration Impact .................................................................................................................................. 165
Step 4: Determine Vibration Mitigation Measures ................................................................................................ 165
SECTION 7: NOISE AND VIBRATION DURING CONSTRUCTION ............................... 172
7.1 C
ONSTRUCTION NOISE ASSESSMENT .......................................................................................................... 172
Step 1: Determine Level of Construction Noise Assessment ...................................................................... 173
Step 2: Use a Qualitative Construction Noise Assessment to Estimate Construction Noise ............. 174
Step 3: Use a Quantitative Construction Noise Assessment to Estimate Construction Noise .......... 174
Step 4: Assess Construction Noise Impact....................................................................................................... 178
Step 5: Determine Construction Noise Mitigation Measures ..................................................................... 179
7.2 C
ONSTRUCTION VIBRATION ASSESSMENT.................................................................................................. 182
Step 1: Determine Level of Construction Vibration Assessment ................................................................ 182
Step 2: Use a Qualitative Construction Vibration Assessment ................................................................... 183
Step 3: Use a Quantitative Construction Vibration Assessment................................................................. 183
Step 4: Assess Construction Vibration Impact................................................................................................. 185
Step 5: Determine Construction Vibration Mitigation Measures............................................................... 186
SECTION 8: DOCUMENTATION OF NOISE AND VIBRATION ASSESSMENT........... 188
8.1 E
NVIRONMENTAL DOCUMENT...................................................................................................................... 188
Step 1: Choose the information to include....................................................................................................... 189
Step 2: Organize information in the Environmental Document ................................................................ 190
8.2 T
ECHNICAL REPORT ON NOISE AND VIBRATION...................................................................................... 192
vii
APPENDIX A GLOSSARY OF TERMS .................................................................................. 195
APPENDIX B FUNDAMENTALS OF NOISE ....................................................................... 200
B.1 A
MPLITUDE ....................................................................................................................................................... 200
B.1.1 D
ECIBEL ADDITION......................................................................................................................................... 201
B.1.2 F
REQUENCY...................................................................................................................................................... 203
B.1.3 T
IME PATTERN.................................................................................................................................................. 205
B.1.4 N
OISE METRICS................................................................................................................................................ 206
B.1.4.1 A-
WEIGHTED SOUND LEVEL: THE BASIC NOISE UNIT................................................................ 206
B.1.4.2 M
AXIMUM SOUND LEVEL (L
MAX
) DURING A SINGLE NOISE EVENT ........................................... 207
B.1.4.3 S
OUND EXPOSURE LEVEL (SEL): EXPOSURE FROM A SINGLE NOISE EVENT ............................ 208
B.1.4.4 E
QUIVALENT SOUND LEVEL (L
EQ(T)
)................................................................................................ 210
B.1.4.5 D
AY-NIGHT SOUND LEVEL (L
DN
): 24-HOUR EXPOSURE FROM ALL EVENTS........................... 214
APPENDIX C BACKGROUND FOR TRANSIT NOISE IMPACT CRITERIA ................... 217
C.1 R
ELEVANT LITERATURE ................................................................................................................................... 217
C.2 B
ASIS FOR NOISE IMPACT CRITERIA CURVES............................................................................................... 218
C.3 E
QUATIONS FOR NOISE IMPACT CRITERIA CURVES................................................................................... 219
APPENDIX D CLUSTERING RECEIVERS OF INTEREST.................................................. 221
APPENDIX E DETERMINING EXISTING NOISE................................................................ 225
APPENDIX F COMPUTING SOURCE LEVELS FROM MEASUREMENTS ...................... 229
F.1 H
IGHWAY AND RAIL VEHICLE PASSBYS........................................................................................................ 229
F.2 S
TATIONARY SOURCES ................................................................................................................................... 233
F.3 L
MAX
FOR SINGLE TRAIN PASSBY..................................................................................................................... 234
APPENDIX G NON-STANDARD MODELING PROCEDURES
AND METHODOLOGY............................................................................................... 237
viii
List of Figures
Figure 3-1 Source-Path-Receiver Framework ........................................................................................................ 9
Figure 3-2 Sound Level Dependence on Speed ...................................................................................................12
Figure 3-3 Attenuation Due to Distance (Divergence)......................................................................................15
Figure 3-4 Attenuation due to Soft Ground.........................................................................................................15
Figure 3-5 Noise Barrier Geometry.......................................................................................................................16
Figure 3-6 Community Reaction to New Noise, Relative to Existing Noise in a Residential Urban
Environment .............................................................................................................................................18
Figure 3-7 Community Annoyance Due to Noise ..............................................................................................18
Figure 4-1 Noise Impact Criteria Flow Chart by Project Segment.................................................................20
Figure 4-2 Noise Impact Criteria for Transit Projects.......................................................................................27
Figure 4-3 Increase in Cumulative Noise Levels Allowed by Criteria (Land Use Cat. 1 & 2)..................30
Figure 4-4 Increase in Cumulative Noise Levels Allowed by Criteria (Land Use Cat. 3)..........................30
Figure 4-5 Procedure for General Noise Assessment .......................................................................................38
Figure 4-6 Curves for Estimating Exposure vs. Distance in General Noise Assessment ..........................48
Figure 4-7 Noise Impacts of Hypothetical Commuter Rail...............................................................................57
Figure 4-8 Example of Project for General Noise Assessment: Siting of Transit Center in Mixed
Commercial/Residential Area...............................................................................................................64
Figure 4-9 Procedure for Detailed Noise Analysis .............................................................................................66
Figure 4-10 Guide to Selecting Noise-Sensitive Receivers of Interest .............................................................67
Figure 4-11 Flow Diagram for Determining Project Noise at 50 ft ..................................................................70
Figure 4-12 Flat Ground...............................................................................................................................................86
Figure 4-13 Source in Shallow Cut............................................................................................................................86
Figure 4-14 Elevated Receiver ....................................................................................................................................86
Figure 4-15 Source in Sloped Cut..............................................................................................................................86
Figure 4-16 Source and Receiver Separated by Trench.......................................................................................86
Figure 4-17 Example Exposure vs. Distance Curves.............................................................................................88
Figure 4-18 Noise Barrier Parameter "P" ................................................................................................................89
Figure 4-19 Recommended Microphone Locations for Existing Noise Measurements ...............................93
Figure 5-1 Propagation of Ground-Borne Vibration into Buildings.............................................................. 109
Figure 5-2 Vibration Signal in Absolute Units.................................................................................................... 111
Figure 5-3 Vibration Signal in RMS Velocity Decibels...................................................................................... 112
Figure 5-4 Typical Levels of Ground-Borne Vibration .................................................................................... 113
Figure 5-5 Response to Transit-Induced Residential Vibration..................................................................... 119
Figure 6-1 Existing Vibration Criteria Flow Chart ........................................................................................... 129
Figure 6-2 Criteria for Detailed Vibration Analysis ......................................................................................... 131
Figure 6-3 Flow Chart of Vibration Screening Process................................................................................... 133
Figure 6-4 Generalized Ground Surface Vibration Curves .......................................................................... 137
Figure 6-5 Ground-Borne Vibration and Noise Model ................................................................................. 154
Figure 6-6 Typical Force Densities for Rail Transit Vehicles, 40 mph ...................................................... 157
Figure 6-7 Typical Force Densities for LRT Vehicles, 40 mph .................................................................... 157
Figure 6-8 Test Configuration for Measuring Transfer Mobility ................................................................. 158
Figure 6-9 Example of Point-Source Transfer Mobility ................................................................................. 159
Figure 6-10 Equipment Required for Field Testing and Laboratory Analysis ............................................. 160
Figure 6-11 Analysis of Transfer Mobility ........................................................................................................... 161
Figure 6-12 Schematic of Transfer Mobility Measurements Using a Line of Impacts .............................. 162
Figure 6-13 Example of Line-source Transfer Mobility ................................................................................... 163
Figure 6-14 Foundation Response for Various Types of Buildings ............................................................... 164
Figure B-1 RMS Pressure Illustration ................................................................................................................. 200
ix
Figure B-2 Graph for Approximate Decibel Addition ................................................................................... 202
Figure B-3 Noise Spectrum of Transit Train on Curve and Elevated Structure ..................................... 204
Figure B-4 A-Weighting Curve ........................................................................................................................... 205
Figure B-5 Typical A-weighted Sound Levels ................................................................................................... 207
Figure B-6 Typical Transit-Vehicle Passby ........................................................................................................ 208
Figure B-7 Typical Fixed-Facility Noice Event ................................................................................................. 208
Figure B-8 An Energy Vice of Noise Events ..................................................................................................... 210
Figure B-9 Typical Hourly L
eq(1hr)
's ...................................................................................................................... 211
Figure B-10 Example A-weighted Sound Level Time Histories ..................................................................... 212
Figure B-11 Typical L
dn
's .......................................................................................................................................... 214
Figure D-1 Example of Receiver Map Showing Cluster Boundaries ........................................................... 224
x
List of Tables
Table 3-1 Noise Metrics...........................................................................................................................................10
Table 3-2 Sources of Transit Noise.......................................................................................................................13
Table 4-1 Multimodal Project Noise Factors ......................................................................................................22
Table 4-2 Multimodal Project Assessment Methods.........................................................................................22
Table 4-3 Land Use Categories and Metrics for Transit Noise Impact Criteria ........................................23
Table 4-4 Levels of Impact.......................................................................................................................................26
Table 4-5 Noise Levels Defining Impact for Transit Projects .........................................................................28
Table 4-6 Noise Impact Criteria: Effect on Cumulative Noise Exposure ....................................................31
Table 4-7 Screening Distance for Noise Assessments......................................................................................35
Table 4-8 Assumptions for Screening Distances for Noise Assessments ....................................................36
Table 4-9 Reference SEL's 50 ft from Track and at 50 mph, One Vehicle...................................................40
Table 4-10 Computation of Noise Exposure at 50 ft for Fixed-Guideway General Noise Assessment 42
Table 4-11 Source Reference Levels at 50 ft from Roadway, 50 mph ............................................................43
Table 4-12 Computation of L
eq(1hr)
and L
dn
at 50 ft for Highway/Transit General Noise Assessment ....44
Table 4-13 Source Reference Levels at 50 ft From the Center of Site, Stationary Sources......................45
Table 4-14 Computation of L
eq(1hr)
and L
dn
at 50 ft for Stationary Source General Noise Assessment ..47
Table 4-15 Distance Correction Factor Equations for General Noise Assessment....................................49
Table 4-16 Computing Total Noise Exposure ......................................................................................................49
Table 4-17 Estimating Existing Noise Exposure for General Noise Assessment .........................................52
Table 4-18 Land Uses of Interest .............................................................................................................................68
Table 4-19 Sources of Transit Noise.......................................................................................................................71
Table 4-20 Source Reference SELs at 50 ft: Fixed-Guideway Sources at 50 mph........................................73
Table 4-21 Computation of L
eq(1hr)
and L
dn
at 50 ft: Fixed-Guideway Sources ..............................................76
Table 4-22 Source Reference SELs at 50 ft: Highway/Transit Sources at 50 mph .......................................78
Table 4-23 Computation of L
eq(1hr)
and L
dn
at 50 ft: Highway/Transit Sources..............................................80
Table 4-24 Source Reference SELs at 50 ft: Stationary Sources.......................................................................82
Table 4-25 Computation of L
eq(1hr)
and L
dn
at 50 ft: Stationary Sources..........................................................83
Table 4-26 Ground Factor G, for Ground Attenuation .....................................................................................86
Table 4-27 Distance Correction Factor Equations for Detailed Noise Analysis ..........................................87
Table 4-28 Barrier Insertion Loss.............................................................................................................................88
Table 4-29 Attenuation due to Buildings................................................................................................................89
Table 4-30 Attenuation due to Trees .....................................................................................................................89
Table 4-31 Calculate L
dn
or L
eq(1hr)
............................................................................................................................91
Table 4-32 Computing Total Noise Exposure ......................................................................................................91
Table 4-33 Transit Noise Mitigation Measures – Source Treatments.............................................................97
Table 4-34 Transit Noise Mitigation Measures – Path Treatments .............................................................. 104
Table 4-35 Transit Noise Mitigation Measures – Receiver Treatments ...................................................... 106
Table 5-1 Ground-borne Vibration and Noise Metrics................................................................................. 110
Table 5-2 Factors that Influence Levels of Ground-Borne Vibration and Noise at the Source
........... 114
Table 5-3 Factors that Influence Levels of Ground-borne Vibration and Noise along the Path ......... 117
Table 5-4 Factors that Influence Levels of Ground-Borne Vibration and Noise at the Receiver ....... 117
Table 5-5 Human Response to Different Levels of Ground-Borne Vibration and Noise ..................... 120
Table 6-1 Land Use Categories for General Vibration Assessment Impact Criteria ............................. 124
Table 6-2 Event Frequency Definitions .............................................................................................................. 125
Table 6-3 Indoor Ground-Borne Vibration (GBV) and Ground-Borne Noise (GBN) Impact Criteria
for General Vibration Assessment................................................................................................... 126
Table 6-4 Indoor Ground-Borne Vibration and Noise Impact Criteria for Special Buildings .............. 126
xi
Table 6-5 Impact Criteria Considering Existing Conditions......................................................................... 128
Table 6-6 Interpretation of Vibration Criteria for Detailed Vibration Analysis ...................................... 131
Table 6-7 Project Types for Vibration Screening Procedure ....................................................................... 135
Table 6-8 Screening Distances for Vibration Assessments........................................................................... 136
Table 6-9 Ground Surface Vibration Level Base Curve Descriptions........................................................ 137
Table 6-10 Generalized Ground Surface Vibration Equations ....................................................................... 138
Table 6-11 Source Adjustment Factors for Generalized Predictions of GB Vibration and Noise ........ 140
Table 6-12 Path Adjustment Factors for Generalized Predictions of GB Vibration and Noise............. 143
Table 6-13 Receiver Adjustment Factors for Generalized Predictions of GB Vibration and Noise..... 145
Table 6-14 Conversion to Ground-borne Noise .............................................................................................. 146
Table 7-1 Construction Equipment Noise Emission Levels.......................................................................... 176
Table 7-2 General Assessment Construction Noise Criteria...................................................................... 179
Table 7-3 Detailed Analysis Construction Noise Criteria............................................................................ 179
Table 7-4 Vibration Source Levels for Construction Equipment ................................................................ 184
Table 7-5 Construction Vibration Damage Criteria....................................................................................... 186
Table C-1 Threshold of Moderate and Severe Impacts ............................................................................... 220
Table F-1 Conversion to Source Reference Levels at 50 ft – Highway and Rail Sources......................231
Table F-2 Conversion to Source Reference Levels at 50 ft – Stationary Sources ................................ 234
Table F-3 Conversion to L
max
at the Receiver, for a Single Train Passby ................................................ 235
xii
List of Examples
Example 4-1 General Noise Assessment – Commuter Rail..............................................................................54
Example 4-2 General Noise Assessment – Highway/Transit............................................................................59
Example 4-3 General Noise Assessment – BRT System....................................................................................60
Example 4-4 General Noise Assessment – Transit Center...............................................................................62
Example 4-5 Detailed Noise Analysis – Fixed Guideway Noise Sources ......................................................77
Example 4-6 Detailed Noise Analysis – Highway Transit Noise Sources......................................................80
Example 4-7 Detailed Noise Analysis – Stationary Noise Sources .................................................................84
Example 4-8 Detailed Noise Analysis – Exposure Vs. Distance Curve..........................................................87
Example 4-9 Detailed Noise Analysis – Shielding ................................................................................................89
Example 4-10 Detailed Noise Analysis – Combine Sources ...............................................................................91
Example 6-1 General Vibration Assessment – LRT ......................................................................................... 148
Example B-1 Decibel Addition – Identical Buses............................................................................................... 203
Example B-2 Decibel Addition – Two Sources ................................................................................................. 203
Example D-1 Clustering Receivers........................................................................................................................ 223
Example F-1 Calculate Sel
ref
– Locomotives....................................................................................................... 232
Example F-2 Calculate Sel
ref
– Rail Cars.............................................................................................................. 232
Example F-3 Calculate Sel
ref
– Bus........................................................................................................................ 233
Example F-4 Calculate Sel
ref
– Signal Crossing................................................................................................... 234
Example F-5 Calculate L
max
– Train Passby......................................................................................................... 236
xiii
Abstract
This report is the third edition of a guidance manual originally issued in 1995. It includes clarifications to
existing policy and updates to outdated references where applicable. Topics presented in this manual
include procedures for predicting and assessing noise and vibration impacts of proposed transit projects
for different stages of project development and different levels of analysis. Additional topics include
descriptions of noise and vibration mitigation measures, construction noise and vibration, and how to
present these analyses in the Federal Transit Administration’s environmental documents. This guidance
is for technical specialists who conduct the analyses, as well as project sponsor staff, Federal agency
reviewers, and members of the general public who may be affected by the projects.
Acknowledgments
The original 1995 version of this manual was developed by the firm Harris Miller Miller & Hanson Inc.
(HMMH) and peer-reviewed by a group of specialists in the fields of acoustics and environmental
planning and analysis. HMMH updated the original manual in 2006.
The updates for this current version were provided by the John A. Volpe National Transportation
Systems Center, Cross Spectrum Acoustics, and FTA, and it was peer-reviewed by a panel of experts.
The U.S. Department of Transportation FTA Office of Planning and Environment wishes to thank the
following for their participation in the peer review of this manual:
Scott Edwar
ds Sha
nkar Rajara
m
A
nthony Eva
ns Judit
h Rocha
t
T
imothy J
ohnson Ja
son R
oss
Sha
nnon McK
enna Hug
h Saurenma
n
La
nce Meist
er Her
bert Singlet
on
James Nelson David Towers
A
nthony Joseph Oss
i
xiv
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
SECTION
1
Introduction
1.1 Purpose
The Council on Environmental Quality (CEQ) regulations for implementing the
procedural provisions of the National Environmental Policy Act of 1969
(NEPA)
(
1
,
2
)
require that a federally-funded project be assessed for its impact on
the human and natural environment prior to implementation. The Federal
Transit Administration (FTA), in conjunction with the Federal Highway
Administration (FHWA), has issued detailed regulations implementing NEPA for
transit and highway projects. The regulations are codified in part 771 of title 23,
Code of Federal Regulations, and are titled “Environmental Impact and Related
Procedures.” (23 CFR part 771).
(
3
)
The Federal Transit Administration (FTA) provides financial assistance for a
range of public transportation projects from new rail rapid transit (RRT)
systems to bus maintenance facilities and vehicle purchases. As required by
NEPA and its implementing regulations, each project must undergo
environmental review.
Noise and vibration are sometimes among the major concerns regarding the
effects of a transit project on the surrounding community and are key elements
of the environmental impact assessment process for public transportation
projects. A transit system is often placed near population centers by necessity
and may cause noise and vibration at nearby residences and other sensitive
types of land use.
This manual provides technical guidance for conducting noise and vibration
analyses for transit projects, as well as direction regarding preparation of the
information for FTA’s environmental documents. Some situations may not be
explicitly covered in this manual; the exercise of professional judgment may be
required to extend the basic methods in these cases and frequent consultation
with FTA staff is important to ensure the methods used meet the requirements
for environmental reviews. See Appendix G for information on using non-
standard modeling procedures.
In general, the noise and vibration impact assessment process for projects
includes the following steps:
1. Determine appropriate impact criteria (Section 4.1).
2. Conduct screening and determine appropriate level of noise analysis,
analyze project noise impacts, and evaluate mitigation options if
appropriate (Sections 4.2–4.5).
3. Determine appropriate level of vibration analysis, analyze project
vibration impacts, and evaluate mitigation options if appropriate
(Sections 6.1–6.5).
4. Analyze construction noise and vibration impacts (Section 7).
5. Document findings (Section 8).
FEDERAL TRANSIT ADMINISTRATION 1
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
1.2 Organization of the Manual
This guidance manual is organized by the following recommended analysis
workflow. A glossary of terms used throughout this manual is available in
Appendix A. Detailed information on the fundamentals of noise, noise impact
criteria, clustering receivers, determining existing noise, computing source levels
from measurements, and using non-standard methodology is available in the
appendices.
Section 2: Project Class of Action and Planning – This section describes
the first step in the analysis process that is applicable to both noise and vibration
analyses.
Section 3: Transit Noise – This section provides the reader with background
information specific to transit noise.
Section 4: Noise Impact Analysis – This section provides a general outline
of the entire noise impact analysis process: guidelines on determining noise
impact criteria, methods for choosing the appropriate level of noise analysis
(“Screening,” “General,” or “Detailed”), steps for evaluating noise impacts with
the Noise Screening Procedure (a simplified method of evaluating the potential
for noise impact from transit projects), steps for evaluating noise impact with
the General Noise Assessment procedure (a simplified assessment method to
estimate noise impact and compare alternatives for transit projects), and steps
for evaluating noise impact with the Detailed Noise Analysis procedure (a
comprehensive assessment method to produce the most accurate estimates of
noise impact intended for certain major public transportation projects).
Section 5: Transit Vibration – This section contains background information
specific to transit vibration.
Section 6: Vibration Impact Analysis – This section provides a general
outline of the entire vibration impact analysis process: guidelines on determining
vibration impact criteria, methods for choosing the appropriate level of
vibration analysis (“Screening,” “General,” or “Detailed”), steps for evaluating
vibration impact with the vibration screening procedure (a simplified method of
evaluating the potential for vibration impact from transit projects), steps for
evaluating vibration impact with the general vibration assessment procedure (a
simplified assessment method to estimate vibration impact and compare
alternatives for transit projects), and steps for evaluating vibration impact with
the detailed vibration analysis procedure (a comprehensive assessment method
to produce the most accurate estimates of vibration impact intended for certain
major public transportation projects).
Section 7: Noise and Vibration During Construction – This section
presents the process of assessing noise and vibration impact during
construction, including determination of level of assessment, source levels,
impact criteria, and mitigation.
Section 8: Documentation of Noise and Vibration Assessment – This
section includes guidance for documenting the noise and vibration assessment in
technical reports and environmental documents.
FEDERAL TRANSIT ADMINISTRATION 2
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
SECTION
2
Project Class of Action and Planning
The level of environmental analysis and review depends on the significance of
any potential associated environmental impacts, which in turn depends in part
on the scope and complexity of the proposed project. The goals of a transit
noise and vibration impact assessment are to:
1. Determine existing noise and vibration levels.
2. Assess project noise and vibration for potential impact.
3. Evaluate the effect of mitigation options on impacts.
The class of action determination will inform the required level of analysis. The
FTA Regional office
(
i
)
determines the class of action based on project
information provided by the project sponsor. The following types of information
can assist the FTA Regional office in an initial class of action determination for a
project:
Project description
Project-specific graphics, including:
Project location/sizes
Known land use and environmental features
Additional information, as appropriate:
Summary of prior planning
Draft purpose and need statement
Project classes of action are described in Section 2.1. Project planning and
development guidelines are presented in Section 2.2.
2.1 Project Class of Action
FTA's environmental regulations classify projects by level of environmental
analysis. The class of action will determine the appropriate level of analysis and
documentation for a project. Details of each class are described in the following
sections. For more information, review FTA's environmental impact and related
procedures at 23 CFR part 771.
Environmental Impact Statements
Environmental impact statements (EISs) apply to projects that are expected to
cause significant environmental effects in the NEPA context. Typical examples
include new or extensions of fixed-guideway projects, such as heavy rail, light
rail, commuter rail, and automated guideway transit (AGT) systems that are not
located within existing transportation right-of-way (ROW). It is likely that for
major infrastructure projects requiring an EIS, the most detailed treatment of
noise and vibration impacts will often be required.
Categorical Exclusions
Categorical exclusions (CEs) cover actions that are excluded from requiring an
EIS or environmental assessment (EA) because FTA has determined that they do
http://www.fta.dot.gov/12926.html.
FEDERAL TRANSIT ADMINISTRATION 3
i
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
not routinely cause significant environmental impacts. FTA’s CEs are located at
23 CFR §§ 771.118(c) and (d), commonly referred to as the c-list and d-list,
respectively. Examples of projects that would normally be CEs include vehicle
purchases, maintenance of equipment, vehicles, or facilities, and ROW
acquisition.
In general, CEs for transit capital construction projects often require at least a
screening of noise impacts.
Environmental Assessments
When a proposed project is presented to FTA and it is uncertain whether the
project requires an EIS or qualifies for a CE, FTA will normally direct the
project sponsor to prepare an environmental assessment (EA) to assist in
making the determination. An EA may be prepared for any type of project if
uncertainty exists about the magnitude or extent of the impacts. Generally, an
EA is selected over a CE if FTA determines that several types of potential
impacts require further investigation, for example, air quality, noise, wetlands,
historic sites, and/or traffic, but FTA’s environmental regulation does not list
typical projects that require EAs.
Experience shows that most of the EAs prepared for transit projects require at
least a general assessment of noise impacts.
2.2 Project Planning and Development
Capital transit projects are ordinarily developed initially from a comprehensive
transportation planning process conducted in metropolitan areas (see 23 CFR §
450.300).
(
4
)
The metropolitan planning process often includes some early
consideration of social, economic, and environmental effects of proposed major
infrastructure improvements. At this stage, environmental effects are usually
considered on a broad scale—for example, overall development patterns,
impacts on green space, and regional air quality. Noise and vibration
assessments are not typically performed at this stage because the proposed
infrastructure improvements lack the necessary detail.
Once the need for a capital transit project in a corridor is established in the
metropolitan transportation plan, the transit mode and general alignment best
suited for the corridor are identified. The Screening and General noise
assessment procedures and the vibration screening procedure described in this
manual may be used to compare noise and vibration effects among different
transit modes and alignments at an early stage of the project planning. The
analysis that results is documented through the environmental review process.
NEPA establishes a broad policy regarding mitigation as a means of
accomplishing its environmental objectives. Other Federal laws, such as Section
4(f) (49 U.S.C. 303) and Section 404 (33 U.S.C. 1344), have explicit mitigation
requirements for certain resources. The decision to include noise or vibration
mitigation for a project is made by FTA and the project sponsor after public
review of the environmental document, as appropriate. If mitigation measures
are deemed necessary to protect the environment or to satisfy statutory
requirements, they will be incorporated as an integral part of the project and
subsequent grant documents will reference these measures as contractual
obligations on the part of the project sponsor. Through that process, FTA
FEDERAL TRANSIT ADMINISTRATION 4
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
ensures that the project sponsor complies with all design and mitigation
commitments contained in the environmental record.
Once the project enters construction, noise or vibration may need to be
reassessed in some circumstances. Some large construction projects in densely
populated residential areas may require noise monitoring to ensure agreed-upon
noise limits are not exceeded. Vibration testing may be needed in the final
stages of construction to determine whether vibration control measures have
the predicted effect.
Considering that transit projects must be located amid or very close to
concentrations of people, noise and vibration impacts can be a concern
throughout the environmental review process, design, and construction phases.
This manual offers the flexibility to address noise and vibration at different
stages in the development of a project and in different levels of detail.
2.3 Mitigation Policy Considerations
Because noise is frequently among the greatest environmental concerns of
planned transit projects, FTA and the project sponsor should make reasonable
efforts to reduce predicted noise to levels considered acceptable for affected
noise-sensitive land uses. The need for noise mitigation is determined based on
the magnitude of impact and consideration of factors specifically related to the
proposed project and affected land uses.
The goal of providing noise mitigation is to gain substantial noise reduction, not
simply to reduce the predicted levels to just below the “severe” impact
threshold. For FTA to determine whether the mitigation is reasonable, the
evaluation of specific mitigation measures should include the noise reduction
potential, the cost, the effect on transit operations and maintenance, and any
other relevant factors, such as any new environmental impacts that may be
caused by the implementation of a noise reduction measure. A thorough
evaluation enables FTA to make the findings required by NEPA and other
statutes, such as Section 4(f) or Section 106 requirements and their
implementing regulations.
Severe impacts have the greatest adverse impact on the community, and
mitigation should be strongly considered. Areas with “moderate” impacts also
have potential for effects on the community and therefore should also include
consideration and possible adoption of mitigation measures when considered
reasonable.
Since reasonableness is not strictly defined, FTA recommends that project
sponsors work with the affected public and FTA staff during the environmental
review process to decide appropriate mitigation strategies. A project sponsor
may also consider developing and formally adopting a mitigation policy to aid in
the determination of appropriate and applicable mitigation measures for current
and proposed projects and anticipated impacts. Having such a policy in place can
aid in the project planning up front and help to expedite mitigation decisions.
FEDERAL TRANSIT ADMINISTRATION 5
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
The following considerations can assist in determining circumstances that trigger
the need for mitigation and include examples of how they can be applied in a
noise mitigation policy:
Number of Noise-Sensitive Sites Affected
A row or cluster of residences adjacent to a rail transit line establishes a
greater need for mitigation than one or several isolated residences in a
mixed-use area. Single residences may not be able to meet a cost-
effectiveness criterion for mitigation.
Example Mitigation Policy Consideration: Set a minimum number of
noise-sensitive sites as a threshold, combined with a reference to a cost-
effectiveness criterion.
Increase over Existing Noise Levels
Since the noise impact criteria are delineated as bands or ranges, project
noise can vary 5 to 7 decibels (dB) within the band of moderate impact at
any specific ambient noise level. If the project and ambient noise plot falls
just below the severe range, the need for mitigation is strongest for a
moderate impact. Similarly, if the plot falls within the moderate range just
above the no impact threshold, the impacts are expected to be less, so the
justification for mitigation would not be as strong.
Example Mitigation Policy Consideration: Set a strong need for
mitigation when a moderate impact is 2 dB (for example) over the no
impact threshold.
Noise Sensitivity of the Property
Section 4.1 includes a comprehensive list of noise-sensitive land uses, yet
there can be differences in noise sensitivity depending on individual
circumstances. For example, parks and recreational areas vary in their
sensitivity depending on the type of use they experience (active vs. passive
recreation) and the settings in which they are located.
Example Mitigation Policy Consideration: Cite the use of the property
as a determination of sensitivity for parks and recreational areas.
Effectiveness of the Mitigation Measure(s)
Determine the magnitude of the noise reduction that can be achieved, and
consider whether there are conditions that limit effectiveness, such as noise
barrier effectiveness for a multi-story apartment building.
Example Mitigation Policy Consideration: Set a minimum reduction in
noise level to be considered effective. A 5-dB reduction is typically
considered an effective reduction from mitigation.
Feasibility of the Mitigation Measure(s)
Determine if the mitigation measure is feasible from an engineering,
operations or safety perspective. In some cases, it may not be possible to
construct mitigation (noise barriers) due to physical or structural limitations
FEDERAL TRANSIT ADMINISTRATION 6
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
or because of safety concerns, especially related to sight lines for
pedestrians and vehicles.
Example Mitigation Policy Consideration: State that the engineering
design of the mitigation must be feasible, that it must be implementable in
light of operations, and that mitigation must not compromise safety.
Fairness and Equity of the Mitigation Measure(s
)
Ens
ure that mitigation measures are applied in a fair and equitable manner
.
In
many cases, small differences in distances or operations can result in smal
l
differences in projected noise levels. For example, all the residences in a
r
ow could have a projected moderate impact except for one residence a
t
the end of the row that falls just under the moderate criteria due to being
s
et slightly further back from the alignment. In a case like this, mitigatio
n
should be applied for the entire row of residences if possible.
E
xample Mitigation Policy Consideration: State that mitigation should be
applied equitably.
Existing Transportation No
ise
Neig
hborhoods with ambient noise levels already heavily influenced
by
t
ransportation noise, especially the same type of noise source as t
he
pr
oject, should be considered. Often adding a new similar noise source wi
ll
not
add to the ambient noise levels or only slightly increase it to wit
hin
a
cceptable levels. Whereas, impacts would be more likely, if the new nois
e
wa
s added to a neighborhood with minimal transportation noise. However
,
it is important to note that per (Section 4.1, Step 3) the higher the existing
nois
e, the lower the allowable noise increase from new sources. A
new
c
umulative noise environment may be very objectionable because pe
ople
wi
ll not be compartmentalizing the existing noise versus the new noise an
d
r
eacting only to the new noise. In this circumstance, impacts predicted
in
t
he moderate range could be treated as if they were sever
e.
E
xample Mitigation Policy Consideration: Set a policy that moderate
impacts under these circumstances be treated as severe and cite the
potential for reducing noise from existing transportation noise, as well as
from project noise.
Community Views
T
his manual provides the methodology to make an objective assessment
of
t
he need for noise mitigation. However, the views of the community sh
ould
be
considered where there are potential noise impacts predicted throug
h
t
his manual. The NEPA compliance process provides the framework f
or
hea
ring the community's concerns about a proposed project and t
hen
mak
ing a good-faith effort to address those concerns. Many projects can
be
expec
ted to have projected noise levels within the moderate impact rang
e
a
nd, where possible, decisions regarding mitigation should be made aft
er
c
onsidering input from the affected public, relevant government agencies
,
a
nd community organizations. There have been cases where the solution t
o
t
he noise problem, a noise barrier, was not preferable to communit
y
members because of perceived adverse visual effects.
FEDERAL TRANSIT ADMINISTRATION 7
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Example Mitigation Policy Consideration: State that community input in
determining the need for mitigation will be included whenever possible.
Implementation Cos
t
Cos
t is an important consideration in reaching decisions about nois
e
mit
igation measures. One guideline for gauging the reasonableness of t
he
c
ost of mitigation is the state DOT’s procedures on the subject. Many stat
es
ha
ve established their own cost threshold per benefited residence f
or
det
ermining whether installation of noise barriers for noise reduction is
a
reasonable expenditure. Several airport authorities have placed limits on the
c
osts they will incur for sound insulation per residence for homes, and FT
A
assesses cost in a similar manner by benefited residence. Higher costs may
be
justified depending on the specific set of circumstances of a project
.
Example Mitigation Policy Consideration: State the adopted cost
threshold per benefited receiver for typical circumstances.
FEDERAL TRANSIT ADMINISTRATION 8
SECTION
3
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Transit Noise
This section presents the basic concepts of transit noise as background for
computation methods and transit noise assessment procedures presented in
Section 4. An overview of fundamental noise topics, including amplitude,
frequency, time pattern, and decibel addition, is presented in Appendix B.
The Source-Path-Receiver framework for noise illustrated in Figure 3-1 is
central to all environmental noise studies. Each transit source generates noise
that depends upon the type of source and its operating characteristics. Along
the propagation path, between all sources and receivers, noise levels can be
reduced (attenuated) by distance depending on ground type, intervening
obstacles, and other factors. Finally, noise combines from multiple sources at
each receiver and potentially interferes with activities at that location.
Figure 3-1 Source-Path-Receiver Framework
This section contains the following:
Section 3.1 presents the noise metrics used in this manual.
Section 3.2 provides an overview of transit noise sources, including a
listing of major sources and a discussion of noise-generation
mechanisms.
Section 3.3 provides an overview of noise paths, including a discussion
of the various attenuating mechanisms on the path between source and
receiver.
Section 3.4 provides an overview of receiver response to transit noise,
including a discussion of the technical background for transit noise
criteria and the distinction between absolute and relative noise impact.
FEDERAL TRANSIT ADMINISTRATION 9
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
3.1 Noise Metrics
This manual uses the noise metrics outlined in Table 3-1 for transit noise
measurements, computations, and assessment. The terminology is consistent
with common usage in the United States. All of these noise metrics are
expressed in units of A-weighted decibels (dBA). A-weighted sound levels
represent the overall noise at a receiver that is adjusted in frequency to
approximate typical human hearing sensitivity. This is the basic noise unit for
transit noise analyses.
Table 3-1 Noise Metrics
Metric
Abbreviation
Definition
A-weighted Sound Level
dBA
A-weighted sound levels represent the overall noise at a receiver that
is adjusted in frequency to approximate typical human hearing
sensitivity. This is expressed as A-weighted decibels (dBA), the basic
noise unit for transit noise analyses.
Sound Exposure Level
SEL
SEL is the cumulative noise exposure from a single noise event,
normalized to one second. SEL contains the same overall sound
energy as the actual varying sound energy during the event. It is the
primary metric for the measurement of transit vehicle noise
emissions, and is an intermediate metric in the measurement and
calculation of both L
eq(t)
and L
dn
.
Equivalent Sound Level
L
eq(t)
The equivalent sound level L
eq(t)
describes a receiver's cumulative
noise exposure from all events normalized to a specified period of
time “t”. L
eq(t)
represents a hypothetical, constant sound level and
contains the same overall sound energy as the actual varying sound
energy during the time period “t”. For transit noise impact
assessments, the equivalent sound level metric is A-weighted and all
events are normalized over a one-hour time period, L
eq(1hr)
. For transit
noise assessments, this metric is appropriate for non-residential land
uses and is computed for the loudest hour of project related activity
during hours of noise sensitivity.
Day-Night Sound Level
L
dn
L
dn
describes a receiver's cumulative noise exposure from all events
over 24 hours. Events between 10 p.m. and 7 a.m. are increased by 10
dB to account for humans’ greater nighttime sensitivity to noise. L
dn
is
used to assess transit noise for residential land uses.
Maximum Sound Level
L
max
The maximum level describes the maximum noise level reached
during a single noise event. For transit noise impact assessments, it is
appropriate to consider the A-weighted maximum level (L
max
) to
understand the full context of the scenario. It is not appropriate to
use this metric for transit noise impact assessments. This metric is
commonly used in vehicle noise specifications and commonly
measured for individual vehicles.
The noise metrics, including their application to transit noise and vibration
impact assessment, are described in more detail in Appendix B.1.4. Mathematical
definitions and graphic illustrations are presented to facilitate understanding and
the interrelationships among metrics.
3.2 Sources of Transit Vehicle Noise
This section discusses major characteristics of the sources of transit noise.
Transit noise can be generated by transit vehicles in motion, stationary transit
FEDERAL TRANSIT ADMINISTRATION 10
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
vehicles, and fixed-transit facilities. Procedures for computing nearby noise
levels for major sources as a function of operating parameters such as vehicle
speed are given in Sections 4.4 and 4.5.
Transit Vehicles in Motion
Transit vehicles most noticeably create noise when in motion. Noise from
transit vehicles in motion can come from multiple sources, including the
propulsion unit (i.e., the engine and engine components), the interaction of the
wheels and/or tires and the running surface, and warning bells and horns.
Vehicle propulsion units generate:
Whine from electric control systems and traction motors that propel
rapid transit cars
Diesel-engine exhaust noise from both diesel-electric locomotives and
transit buses
Air-turbulence noise generated by cooling fans
Gear noise
Noise is also generated by the interaction of wheels and/or tires with their
running surfaces. Tire noise from rubber-tired vehicles is generated at normal
operating speeds. The interaction of steel wheels and rails generates:
Rolling noise due to continuous rolling contact
Impact noise when a wheel encounters a discontinuity in the running
surface such as a rail joint, turnout or crossover (where the train or rail
vehicle switches off one track and onto another)
Impact noise from the wheel and running surface if the wheel is not
completely round (wheel flat) or if the running surface is not completely
flat
Squeal generated by friction between wheels and rail on tight curves
Transit vehicles are equipped with horns and bells for use in emergency
situations and as a general audible warning to track workers and trespassers
within the ROW, pedestrians, and motor vehicles at highway grade crossings.
Horns and bells on the moving transit vehicle combined with stationary bells at-
grade crossings can generate high noise levels for nearby residents and are often
sources of complaints.
For many noise sources, such as transit vehicles, the sound level is dependent
on the speed of the noise source. In other cases, such as for stationary sources
or horns mounted on vehicles, the sound level is not dependent on speed.
Figure 3-2 illustrates sound level dependence on speed for a diesel-powered
commuter rail train and an electric-powered transit train assuming all other
parameters, such as weight, are equal. Plotted vertically in this figure is a
notional indication of the maximum sound level during a passby. Speed
dependence is strong for electric-powered transit trains because wheel/rail
noise is the dominant noise source and noise from this type of source increases
strongly with speed. Diesel-powered commuter rail train noise is dominated by
the locomotive exhaust noise at slower speeds. As speed increases, wheel-rail
FEDERAL TRANSIT ADMINISTRATION 11
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
noise becomes the dominant noise source and diesel- and electric-powered
trains generate similar noise levels. Similarly, speed dependence is also strong
for automobiles, city buses (two-axle), and non-accelerating highway buses
(three-axle), because tire/pavement noise is the dominant noise source for
these vehicles. Accelerating highway bus noise is dominated by exhaust noise.
Figure 3-2 Sound Level Dependence on Speed
Sound levels close to the source are also dependent on vehicle acceleration,
vehicle length, running surface type, and running surface condition. For high-
speed rail vehicles (vehicles with an operating speed of 90–250 mph are typically
beyond the scope of this manual), air turbulence can also be a source of noise.
In addition, for an elevated structure, the guideway can radiate noise as it
vibrates in response to the dynamic loading of the moving vehicle.
Stationary Transit Vehicles
Noise can be generated by transit vehicles even when they are stationary. For
example, auxiliary equipment such as cooling fans on motors, radiator fans, plus
hydraulic, pneumatic, and air-conditioning pumps, often continue to run when
vehicles are stationary. Transit buses are also often left idling in stations or
storage yards.
Fixed-transit Facilities
Noise can also be generated by sources at fixed-transit facilities. Such sources
include ventilation fans in transit stations, subway tunnels, and electric power
substations, as well as equipment in chiller plants, and many activities within
maintenance facilities and shops.
Common Noise Sources
Table 3-2 summarizes common sources of transit noise by vehicle and facility
type.
FEDERAL TRANSIT ADMINISTRATION 12
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Table 3-2 Sources of Transit Noise
Vehicle or Facility*
Dominant Components
Comments
RRT or Light Rail Transit
(LRT) on exclusive ROW
Wheel/rail interaction and
guideway amplification
Depends on condition of wheels and rails
Propulsion system
When accelerating and at higher speeds
Brakes
When stopping
Auxiliary equipment
When stopped
Wheel squeal
On tight curves
In general
Noise increases with speed and train length
LRT in Mixed Traffic
Wheel squeal
On tight curves
Auxiliary equipment
When stopped
Horns and crossing bells
At-grade crossings and stations
In general
Traveling at lower speeds in mixed traffic
produces less noise than when traveling at
higher speeds in exclusive ROW
Commuter Rail
Diesel exhaust
On diesel-hauled trains
Cooling fans
On both diesel and electric-powered trains
Wheel/rail interaction
Depends on condition of wheels and rails
Horns and crossing gate bells
At-grade crossings and stations
In general
Noise is usually dominated by locomotives and
horns/bells at-grade crossings
Low and Intermediate
Capacity Transit
Propulsion systems, including
speed controllers
At low speeds
Ventilation systems
At low speeds
Tire/guideway interaction
For rubber-tired vehicles, including monorails
Wheel/rail interaction
Depends on condition of wheels and rails
In general
Wide range of vehicles: monorail, rubber-
tired, steel-wheeled, linear induction. Noise
characteristics depend upon type
Diesel Buses
Cooling fans
While idling
Engine casing
While idling
Diesel exhaust
At low speeds and while accelerating
Tire/roadway interaction
At moderate and high speeds
In general
Includes city buses (generally two-axle) and
commuter buses (generally three-axle)
Electric Buses and
Trackless Trolleys
Tire/roadway interaction
At moderate speeds
Electric traction motors
At moderate speeds
In general
Much quieter than diesel buses
Bus Storage Yards
Buses starting up
Usually most disruptive in the early morning
Buses accelerating
Usually near entrances/exits and/or locations
that require buses to accelerate (tight turns)
Buses idling
Warm-up areas
In general
Site specific: often peak periods with
considerable noise
Rail Transit Storage Yards
Wheel squeal
On tight curves
Wheel impacts
On joints and switches
Wheel rolling noise
On tangent track
Auxiliary equipment
Throughout day and night; includes air-break
release noise
Coupling/uncoupling
On storage tracks
Signal horns
Throughout yard site
In general
Site specific: often early morning and peak
periods with considerable noise
FEDERAL TRANSIT ADMINISTRATION 13
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Maintenance Facilities
Signal horns
Throughout facility
Intercoms
Throughout facility
Impact tools
Shop buildings
Car/bus washers/driers
Wash facility
Vehicle activity
Throughout facility
In general
Site specific: considerable activity throughout
day and night, some outside.
Stations
Automobiles
Patron arrival/departure, especially in early
morning
Buses idling
Bus loading zone
Intercoms
Platform area
Locomotive idling
At commuter rail terminal stations
Auxiliary systems
At terminal stations and layover facilities
Horns
At stations, if applicable
In general
Site specific, with peak activity periods
Subways
Fans
Noise through vent shafts/structures
Buses/trains in tunnels
Noise through vent shafts/structures
In general
Noise is not a problem, except in the
immediate vicinity of vent shafts/structures.
* Refer to Appendix A for additional information.
3.3 Paths of Transit Noise from Source to
Receiver
This section contains a qualitative overview of noise-path characteristics from
source to receiver, including attenuation along these paths. Equations for
specific noise-level attenuations along source-receiver paths are included in
Sections 4.4 and 4.5.
Sound paths from source to receiver are predominantly through the air. Along
these paths, sound reduces with distance due to divergence,
absorption/diffusion, and shielding. These mechanisms of sound attenuation are
discussed below.
Divergence
Sound levels naturally attenuate with distance, as shown in Figure 3-3. The plot
shows attenuation at the receiver relative to the sound level 50 ft from the
source. This type of attenuation is called divergence and is dependent upon
source configuration (line or point source) or other source-emission
characteristics. Localized sources (point sources) grouped closely together
attenuate greatly with distance at a rate of approximately 6 dB per doubling of
distance. Examples of point sources include highway grade-crossing signals along
rail corridors, intercoms in maintenance yards and other closely grouped
sources of noise. Vehicles passing along a track or roadway forming a line are
called line sources. Line sources attenuate less than point sources with distance.
Rate of attenuation for line sources varies depending on the noise metric. L
eq(1hr)
and L
dn
noise levels attenuate at a rate of 3 dB per doubling of distance and L
max
noise levels attenuate at a rate of 3 to 6 dBs per doubling of distance.
Figure 3-3 illustrates approximate attenuation with distance between the source
and receiver for point and line sources. The line source curve for the
L
max
noise
FEDERAL TRANSIT ADMINISTRATION 14
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
metric separates into three curves because it is dependent on the length of the
line source. Equations for the curves in Figure 3-3 are included in Section 4.5.
Figure 3-3 Attenuation Due to Distance (Divergence)
Absorption/Diffusion
In addition to distance, sound levels can be attenuated depending on the type of
ground between the source and receiver. A portion of the sound energy is
absorbed by the ground and only the remaining energy travels to the source.
How much energy the ground absorbs is dependent on the ground type
(characterized as acoustically “hard” or “soft”) and geometry. Example
absorptive ground types include freshly-plowed or vegetation-covered ground.
Figure 3-4 illustrates approximate attenuation due to ground type by source to
receiver path distance and height. Ground attenuation can be as large as 5 dB
over a path distance of several hundred ft. At very large distances, wind and
temperature gradients could modify the expected ground attenuation. However,
these variable atmospheric effects are not included in this manual because they
generally occur beyond the range of typical transit-noise impact. Equations for
the curves in this figure are included in Section 4.5.
Figure 3-4 Attenuation due to Soft Ground
Shielding
Sound paths are sometimes interrupted by terrain, human-constructed noise
barriers, rows of buildings, or other objects. Noise barriers are one of the most
effective means of mitigating noise (Section 4.5, Step 7). A noise barrier reduces
sound levels at a receiver by breaking the direct line-of-sight between source
and receiver with a solid wall (in contrast to vegetation which hides the source
from view but does not reduce sound levels substantially over short distances).
Sound energy reaches the receiver only by bending (diffracting) over the top of
FEDERAL TRANSIT ADMINISTRATION 15
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
the barrier, as shown in Figure 3-5. This diffraction over the barrier reduces the
sound level that reaches the receiver. One important consideration in using
noise barriers to mitigate noise impacts is safety. Noise barriers, if not designed
and sited carefully, can reduce visibility of trains for pedestrians and motorists,
leading to less safe conditions. It is important to consult with safety experts
when choosing and siting a noise barrier.
Noise barriers for transportation systems are typically used to attenuate noise
at the receiver, potentially reducing received sound levels by 5 to 15 dB,
depending upon barrier height, length, and distance from both source and
receiver. Barriers on structures close to the transportation noise source may
provide less attenuation than barriers located farther from the source due to
reverberation (multiple reflections) between the barrier and the body of the
vehicle or noise source. This reverberation can be offset by increased barrier
height and/or acoustical absorption on the source side of the barrier. Further
discussion and equations on acoustical absorption and barrier attenuation is
provided in Section 4.5.
Source-to-receiver sound paths may not always travel through the air, but
rather through the ground or through structural components of the receiver's
building. Discussion of such ground-borne and structure-borne propagation is
included in Section 5.
Figure 3-5 Noise Barrier Geometry
3.4 Receiver Response to Transit Noise
This section contains an overview of human receiver response to noise. It
serves as background information for the noise impact criteria in Section 4.1.
Noise can interrupt ongoing activities causing community annoyance, especially
in residential areas. In general, most residents become highly annoyed when
noise interferes considerably with activities such as sleeping, talking, noise-
sensitive work, and audio entertainment. In addition, some land uses, such as
outdoor concert pavilions, are inherently incompatible with high noise levels.
FEDERAL TRANSIT ADMINISTRATION 16
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Annoyance from noise has been investigated and approximate dose-response
relationships have been quantified by the U.S. Environmental Protection Agency
(EPA).
(
5
)
The selection of noise metrics in this manual is largely based upon this
EPA work. Beginning in the 1970s, the EPA undertook a number of research and
synthesis studies relating to community noise of all types. Results of these
studies have been widely published, discussed, and refereed by many
professionals in acoustics. Basic conclusions of these studies have been adopted
by the Federal Interagency Committee on Noise (FICON),
(
ii
)
the U.S.
Department of Housing and Urban Development (HUD), the American
National Standards Institute, and even internationally
(
6
)(
7
)(
8
)(
9
).
Conclusions from
this seminal EPA work remain scientifically relevant today.
Figure 3-6 contains a synthesis of actual case studies of community reaction to
newly introduced sources of noise in a residential urban neighborhood.
(
10
)
Plotted horizontally in the figure is the increase in noise from new sources
above existing noise levels expressed as Day-Night Sound Levels, L
dn
, discussed
in Appendix B.1.4.5. Plotted vertically is the community reaction to this newly
introduced noise. As shown in the figure, community reaction varies from no
reaction to vigorous action for newly introduced noises averaging from 10 dB
below existing to 25 dB above existing. Note the assumptions included in the
graphic are associated with the specific data points from the study. These
assumptions are generally appropriate to give context to most transit projects,
but community reaction may differ for conditions specific to each project.
In many community attitudinal surveys, transportation noise has been ranked
among the greatest causes of community dissatisfaction. A synthesis of many
such surveys on annoyance is shown in Figure 3-7.
(
11
)(
12
)
Noise exposure levels
are plotted against the percentage of people who are highly annoyed by the
particular level of neighborhood noise. As shown in the figure, the percentage of
high annoyance is approximately 0 percent at 45 dB, 10 percent around 60 dB,
and increases quite rapidly to approximately 70 percent around 85 dB. The
scatter about the synthesis line is due to community variation and wording
differences in the surveys. An update of the original research containing
additional railroad, transit and street traffic noise surveys generally follows the
shape of the original response curve shown in Figure 3-7.
(12)(
13
)
As indicated by Figure 3-6 and Figure 3-7, introduction of certain levels of
transit noise into a community may have two undesirable effects. First, it may
substantially increase noise levels above existing noise levels in a community.
This effect is called a relative noise impact. Evaluation of this effect compares
new noise levels to the existing levels. Criteria for a relative noise impact
evaluation are based upon noise increases above existing levels. Second, newly
introduced transit noise may interfere with community activities independent of
existing noise levels. For example, it may be too loud to converse or sleep. This
effect is called absolute noise impact and is expressed as a fixed level threshold
that is not to be exceeded. The fixed level threshold is determined
independently of existing noise levels. Relative and absolute noise impacts are
discussed in terms of transit noise criteria in Section 4.1, Step 3.
ii
The Federal Interagency Committee on Aviation Noise (FICAN) is the current version of this group.
FEDERAL TRANSIT ADMINISTRATION 17
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Figure 3-6 Community Reaction to New Noise, Relative to Existing
Noise in a Residential Urban Environment
Figure 3-7 Community Annoyance Due to Noise
FEDERAL TRANSIT ADMINISTRATION 18
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
SECTION
4
Noise Impact Analysis
The FTA noise impact analysis process is a multi-step process used to evaluate
the project for potential noise impacts for FTA NEPA approvals. If impact is
determined, measures necessary to mitigate adverse impacts must be
considered for incorporation into the project.
(4)
It is recommended that project
sponsors develop and formally adopt a policy for determining the need for
mitigation for situations that are loosely covered by the impact criteria.
Considerations for mitigation policies are included in Section 2.3. The FTA noise
impact analysis steps are summarized as follows and are described in the
subsequent subsections:
4.1: Determine noise impact criteria.
Step 1: Identify the type of project/dominant noise source (transit or
multimodal).
Step 2: Choose land use category for FTA criteria.
4.2: Determine the highest appropriate level of noise analysis for the current
stage of project planning or development.
4.3: Evaluate for the potential of impact according to the Noise Screening
Procedure.
Step 1: Identify project type.
Step 2: Determine the screening distance.
Step 3: Identify the study area.
Step 4: Locate noise-sensitive land uses.
4.4: Evaluate impact according to the General Noise Assessment and evaluate
preliminary mitigation options if impact is found.
Step 1: Identify noise-sensitive receivers.
Step 2: Determine the project noise source reference levels.
Step 3: Estimate project noise exposure by distance.
Step 4: Combine noise exposure from all sources.
Step 5: Measure existing noise exposure.
Step 6: Inventory noise impacts.
Step 7: Determine noise mitigation needs.
4.5: Evaluate for impact according to the Detailed Noise Analysis and evaluate
mitigation options if impact is found.
Step 1: Identify noise-sensitive receivers.
Step 2: Determine noise source levels for detailed analysis.
Step 3: Calculate project noise exposure by distance.
Step 4: Combine noise exposure from all sources.
Step 5: Determine existing noise exposure.
Step 6: Assess noise impact.
Step 7: Determine noise mitigation measures.
In addition to analyzing for potential noise impacts, analyze the project for
potential vibration impacts according to the process presented in Section 6.
After both the noise and vibration analyses have been completed, assess
FEDERAL TRANSIT ADMINISTRATION 19
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
construction noise and vibration according to Section 7 and document findings
according to Section 8.
4.1 Determine Noise Impact Criteria
This section describes the procedure for determining the appropriate criteria
for assessing project noise impact based on the type of project and project
noise source. Project noise is the new noise or change in noise introduced by
the project. Noise impact criteria may vary for different segments of the
project. Project segments can be portions of a project with similar
characteristics.
The procedure to determine the appropriate impact criteria is described in this
section and shown more simply as a flow chart in Figure 4-1. If there is
uncertainty in how to determine the appropriate criteria, contact the FTA
Regional office.
The selected criteria are used in the analysis procedures discussed in Sections
4.3, 4.4, and 4.5 to identify potential impacts and the level of impact.
Yes
No
Transit
only?
Figure 4-1 Noise Impact Criteria Flow Chart by Project Segment
FEDERAL TRANSIT ADMINISTRATION 20
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Step 1: Identify Project Type
Identify the type of project as transit, multimodal (transit and highway), or other
multimodal according to the dominant noise source.
Option A: Transit Project (Transit Noise Only) – The transit project
category includes all transit projects where the project noise is exclusively due
to new transit sources, no changes are made to the highway or to existing
highway noise barriers, and the existing noise levels generated by roadway
sources will not change because of the project. For these transit projects, FTA
is the lead agency conducting the environmental review in cooperation with the
transit agency.
Typical examples of transit projects include:
RRT, LRT, commuter rail, and AGT
Rail projects built within an existing highway or railroad corridor that
do not alter the existing noise levels generated by roadway sources
Bus facility projects with operations on local streets and highways used
to access the facility, where the project does not include roadway
construction or modification that changes roadway capacity substantially
Fixed facilities including storage and maintenance yards, passenger
stations and terminals, parking facilities, and substations
Portions of transit projects not adjacent to highway corridors
FTA impact criteria are appropriate for transit projects, proceed to Step 2.
Option B: Multimodal Project (Transit and Highway Noise) – In this
manual, “multimodal” refers to projects that include changes to both transit and
highway components, resulting in project noise comprised of both highway and
transit noise sources.
Typical examples of multimodal projects include:
New highway construction providing general-purpose lanes as well as
dedicated bus and high occupancy vehicle (HOV) lanes
Rail transit projects that involve changes to the highway travel lanes or
existing highway noise barriers
Evaluate multimodal projects for impact according to the project noise source
by project segment. FHWA’s noise assessment methods are used to inform
FTA’s NEPA evaluation only for segments where highway noise levels change
due to the transit project. These projects are not necessarily subject to
FHWA’s procedures at 23 CFR part 772 (see call out box below). For segments of
the project outside the highway corridor, use FTA’s criteria and methods. Use
Table 4-1 to determine multimodal project noise.
Once the project noise source(s) is identified, determine the appropriate
assessment method according to Table 4-2.
FEDERAL TRANSIT ADMINISTRATION 21
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Note that a separate noise analysis may be required for FHWA approval of a multimodal project
pursuant to 23 CFR part 772. For these projects, it is important to work with FHWA early in
the environmental review process to determine how a noise assessment will be completed
where FHWA approval is needed for the project.
The determination of whether a project is subject to FHWA procedures at 23 CFR part 772
depends upon the specific circumstances of a project. A proposed transit project that would
share an existing highway ROW is not necessarily a FHWA-defined multimodal project. A transit
project that meets all three of the following criteria is not considered a multimodal project
subject to 23 CFR part 772:
FTA is the lead agency in the NEPA process and FHWA's limited participation is as a
cooperating agency.
The main transportation purpose of the project, as stated in the purpose and need
statement of the environmental document, is transit-related and not highway-related.
No Federal-aid highway funds are being used to fund the project.
Table 4-1 Multimodal Project Noise Factors
Factor
Description
Volume of
Traffic
Major freeways and interstate highways often carry large volumes of traffic
throughout the day and night such that the highway noise dominates at all
times. Transit noise in this case may be unimportant by comparison, but must
still be evaluated using FTA’s noise criteria for a potential impact.
Traffic Patterns
Some highways and arterials serve primarily as commuter routes such that
nighttime traffic diminishes considerably, while transit systems continue to
operate well into the late hours. Here the dominant noise source at times of
maximum sensitivity may be transit.
Type of Traffic
Some highways and arterials may serve commuters during the daytime hours,
but provide access to business centers by trucks at night. In this case, the
roadway noise would likely continue to dominate.
Alignment
Configuration
Elevation of the transit mode in the median or beside a busy highway may
result in transit noise contributing more noise to nearby neighborhoods than a
highway that may be partially shielded by rows of buildings adjacent to the
ROW. In this case, both transit and highway noise may be considered
dominant.
Table 4-2 Multimodal Project Assessment Methods
Dominant
Noise Source
Assessment Method
Transit, at
All Times
Use FTA criteria and methods. Proceed to Step 2.
Highway, at
All Times
Use FHWA criteria and methods to inform FTA’s NEPA evaluation. Contact
FHWA directly for assistance using FHWA noise analysis methods and FHWA noise
impact criteria.
Transit and
Highway at
Different Times
Use both the FHWA and FTA methods to determine if one, both, or neither
method determines impact due to the project noise for these segments. Note
that the project noise includes both highway and transit sources associated
with the project. Both methods are used because the FTA methods consider
nighttime sensitivity while the FHWA methods consider the peak traffic hour.
Proceed to Step 2 for FTA criteria. Contact FHWA directly for assistance using FHWA
noise analysis methods and FHWA noise impact criteria.
FEDERAL TRANSIT ADMINISTRATION 22
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Option C: Other Multimodal Projects – For projects with components
from other modes, contact the FTA Regional office. Additional information on
high-speed rail vibration and noise can be found in the Federal Railroad
Administration (FRA) “High-Speed Ground Transportation Noise and Vibration
(
14
)
Impact Assessment” guidance manual.
Step 2: Choose Land Use Category for FTA Criteria
Determine the appropriate noise-sensitive land use category for the project segment
using Table 4-3 and the descriptions below then, proceed to Step 3. FTA criteria are
presented by land use.
Table 4-3 Land Use Categories and Metrics for Transit Noise Impact Criteria
Land Use
Category
Land Use
Type
Noise
Metric, dBA
Description of Land Use Category
1
High
Sensitivity
Outdoor
L
eq(1hr)
*
Land where quiet is an essential element of its intended
purpose. Example land uses include preserved land for
serenity and quiet, outdoor amphitheaters and concert
pavilions, and national historic landmarks with
considerable outdoor use. Recording studios and concert
halls are also included in this category.
2
Residential
Outdoor L
dn
This category is applicable all residential land use and
buildings where people normally sleep, such as hotels and
hospitals.
3
Institutional
Outdoor
L
eq(1hr)
*
This category is applicable to institutional land uses with
primarily daytime and evening use. Example land uses
include schools, libraries, theaters, and churches where it
is important to avoid interference with such activities as
speech, meditation, and concentration on reading
material. Places for meditation or study associated with
cemeteries, monuments, museums, campgrounds, and
recreational facilities are also included in this category.
* L
eq(1hr)
for the loudest hour of project-related activity during hours of noise sensitivity.
Noise-sensitive land use categories are described in in order of sensitivity. Most
commercial or industrial uses are not considered noise-sensitive because
activities within these buildings are generally compatible with higher noise levels.
Business can be considered noise-sensitive if low noise levels are an important
part of operations, such as sound and motion picture recording studios.
For residential land use (category 2), apply the noise criteria at the nearest
façade of the occupied portion of the building, e.g., not at a garage or porch.
The residential criteria should be applied at locations with nighttime sensitivity.
For major noise-sensitive outdoor use at non-residential locations, apply the
noise criteria at the point of noise-sensitive use nearest the noise source.
Land use categories are evaluated using noise metrics that reflect the noise-
sensitive time of day:
Categories 1 and 3 – The noise metric,
L
eq(1hr)
is used for all category 1
and 3 land uses where nighttime sensitivity is not a factor. Category 3
land uses are considered less noise-sensitive than category 1 land uses.
For transit analyses,
L
eq(1hr)
is computed for the noisiest hour of transit-
FEDERAL TRANSIT ADMINISTRATION 23
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
related activity during which human activities occur at the noise-
sensitive location. See Appendix B.1.4.4 for more information on this
metric.
Category 2 – The noise metric L
dn
is a used for all category 2 land uses
where nighttime sensitivity is a factor. This noise metric includes a 10-
dB penalty for nighttime noise. See Appendix B.1.4.5 for more
information on this metric.
Land Use Categories: Special Cases
Historic sites, parks, indoor-only land use, and undeveloped land require special
consideration. In addition to NEPA, noise impacts may need to be considered
under other environmental laws such as Section 106
(
15
)
or Section 4(f).
(
16
)
Indoor-only use and undeveloped land should be evaluated on a case-by-case
basis to determine noise sensitivity based on how each facility is used or the
reason it is protected under the applicable requirement.
Historic Sites – Section 106 requires Federal agencies to evaluate potential
effects from projects on historic properties. Per the regulations at 36 CFR part
800,
(
17
)
historic properties are defined as any prehistoric or historic district, site,
building, structure, or object included in, or eligible for the National Register of
Historic Places (NRHP). An adverse effect determination under Section 106 is
made when a project may alter, directly or indirectly, any of the characteristics
of a historic property that qualify the property for inclusion in the National
Register in a manner that would diminish the integrity of the property’s location,
design, setting, materials, workmanship, feeling, or association.
Under FTA environmental reviews, some structures may be evaluated as noise-
sensitive resources per this noise manual and evaluated as historic properties
under Section 106. However, because this manual and Section 106 regulations
have different criteria for effect, identifying a severe noise impact for a structure
under this manual does not necessarily mean there would be an adverse effect
under Section 106. It is important to thoroughly document the characteristics of
historic properties that qualify for inclusion in the NRHP for evaluation of effect
under Section 106.
If a property, for example, is listed on the NRHP under criterion C because the
structure possesses high artistic values, but lacks integrity of setting, feeling, or
association, it is unlikely that a change in the noise environment would affect the
features that qualify the property for listing or eligibility for inclusion in the
NRHP.
In the assessment of effects on historic properties, consideration should be
given to not just the proposed transit project, but any associated mitigation
measures with the transit project. For example, if a transit project would
involve noise walls or berms as mitigation, the effect of those structures on the
visual setting may need to be considered in a Section 106 analysis.
Parks – Most parks used primarily for active recreation such as sports
complexes and bike or running paths are not considered noise-sensitive.
FEDERAL TRANSIT ADMINISTRATION 24
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
However, some parks (even some in dense urban areas) are primarily used for
passive recreation such as reading, conversation, or meditation. These places,
which may be valued as havens from the noise and rapid pace of everyday city
life, are treated as noise-sensitive, and are included in land use category 3.
Consult the state or local agency with jurisdiction over the park on questions
about how the park is used, and visit the park to observe its use, if possible.
Indoor-Only Use – The land use categories described in this section
correspond with noise impact criteria that provide protection for both outdoor
and indoor land uses. For locations where noise impact will be evaluated but
there is no outdoor land use such as apartment buildings, hotels or upper levels
of multi-story buildings, indoor criteria can be used. In these cases, the criterion
for indoor noise levels from project sources is a L
dn
of 45 dBA.
(
18
)
This criterion
is consistent with the Federal Aviation Administration (FAA). See Section 4.5 for
more information on how indoor criteria apply to noise mitigation
consideration.
Undeveloped Land – Undeveloped land may also need to be considered for
noise impact assessment and mitigation if plans are under way to develop the
land for noise-sensitive use. The policy for considering such land for assessment
and mitigation should be determined on a project-specific basis by the project
sponsor in consultation with the FTA Regional office.
Step 3: Determine Appropriate FTA Criteria Presentation
FTA criteria for noise impact were developed specifically for transit noise
sources operating on fixed-guideways or at fixed facilities in urban areas. These
criteria are based on well-documented research on human response to
community noise and represent a reasonable balance between community
benefit and project costs. These criteria do not reflect specific community
attitudinal factors. See Appendix C for additional background information on the
development of FTA noise criteria.
The criteria specify a comparison of future project noise with existing noise.
Note that projections of future noise exposure without the project (no-build
scenario) are not included in this analysis. The criteria also consider land use
which is an important factor that reflects noise sensitivity based on activity and
time period of concern. The criteria are defined with the expectation that
communities already exposed to high levels of noise can only tolerate a small
increase. In contrast, if the existing noise levels are low, it is reasonable to allow
a greater change in the community noise.
The levels of impact are described in Table 4-4. The criteria at which the levels
of impact occur are presented in two ways depending on the relationship of
project and existing noise sources.
If the project noise source is a new source of transit noise in the community, such as a
new project in an area currently without transit, use the criteria as presented in Option
A. If the project noise adds to or changes existing transit noise in the community, use
the criteria as presented in Option B.
FEDERAL TRANSIT ADMINISTRATION 25
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Table 4-4 Levels of Impact
Level of Impact
Description
No Impact
Project-generated noise is not likely to cause community annoyance. Noise
projections in this range are considered acceptable by FTA and mitigation is
not required.
Moderate Impact
Project-generated noise in this range is considered to cause impact at the
threshold of measurable annoyance. Moderate impacts serve as an alert to
project planners for potential adverse impacts and complaints from the
community. Mitigation should be considered at this level of impact based on
project specifics and details concerning the affected properties.
Severe Impact
Project-generated noise in this range is likely to cause a high level of
community annoyance. The project sponsor should first evaluate alternative
locations/alignments to determine whether it is feasible to avoid severe impacts
altogether. In densely populated urban areas, evaluation of alternative locations
may reveal a trade-off of affected groups, particularly for surface rail
alignments. Projects that are characterized as point sources rather than line
sources often present greater opportunity for selecting alternative sites. This
guidance manual and FTA's environmental impact regulations both encourage
project sites which are compatible with surrounding development when
possible. If it is not practical to avoid severe impacts by changing the location of
the project, mitigation measures must be considered.
Option A: Project Noise Impact Criteria Presentation – The impact
criteria presentation for evaluating existing noise independently to project noise
is presented in this option.
The noise levels at which impacts occur are presented in Figure 4-2 and Table
4-5. Equations for the impact criteria are presented in Appendix C. If impact
is
det
ermined, measures necessary to mitigate impacts are to be considered f
or
inc
orporation into the project.
(3)
Figure 4-2 presents the existing noise exposure on the horizontal axis and
project noise on the vertical axis. Category 1 and 2 land uses have the same
criteria for project noise and are on the primary vertical axis. Category 3 land
use criteria are presented on the secondary vertical axis. Note that project
noise for category 1 and 3 land uses is expressed as L
eq(1hr)
, whereas project
noise for category 2 land use is expressed as L
dn
. Also, note that project noise
criteria are 5 dB higher for category 3 land uses in Figure 4-2 since these types
of land use are less noise-sensitive than those in categories 1 and 2.
Note that for projects in locations with existing noise levels below 55 dBA, the
project noise exposure is allowed some increase over the existing noise
exposure before it is considered to cause impact. For category 1 and 2 land
uses, the maximum project noise level to be considered to cause no impact is
65 dBA (L
eq(1hr)
or L
dn
) regardless of the existing noise. Note that no impact at
65 dBA aligns with other Federal agencies in that a L
dn
of 65 dBA is a standard
limit for an acceptable living environment among some Federal agencies.
(
19
) (
20
)
Project noise levels above the top curve are considered to cause severe impact.
The upper limit of the severe impact range is 75 dBA for category 1 and 2 land
uses. The upper limit of 75 dBA is associated with an unacceptable living
environment. Project noise between the two curves is considered to have
moderate impact on the community.
FEDERAL TRANSIT ADMINISTRATION 26
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
The criteria are also tabulated in Table 4-5. Figure 4-2 and the equations that
correspond with this figure in Appendix C are the precise definition of the
criteria. The values in Table 4-5 can be used for illustrative purposes and should
only be used if all numbers are rounded up to the nearest decibel.
Figure 4-2 Noise Impact Criteria for Transit Projects
FEDERAL TRANSIT ADMINISTRATION 27
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Table 4-5 Noise Levels Defining Impact for Transit Projects
Existing
Noise
Exposure,
dBA
Project Noise Impact Exposure, dBA
Category 1 (L
eq(1hr)
) or 2 (L
dn
) Sites
Category 3 Sites (L
eq(1hr)
)
L
eq(1hr)
or L
dn
No
Impact
Moderate
Impact
Severe
Impact
No
Impact
Moderate
Impact
Severe
Impact
<43
<
Ambient+10
Ambient +10 to 15
>
Ambient+15
<
Ambient+15
Ambient +15 to 20
>
Ambient+20
43
<52
52-58
>58
<57
57-63
>63
44
<52
52-58
>58
<57
57-63
>63
45
<52
52-58
>58
<57
57-63
>63
46
<53
53-59
>59
<58
58-64
>64
47
<53
53-59
>59
<58
58-64
>64
48
<53
53-59
>59
<58
58-64
>64
49
<54
54-59
>59
<59
59-64
>64
50
<54
54-59
>59
<59
59-64
>64
51
<54
54-60
>60
<59
59-65
>65
52
<55
55-60
>60
<60
60-65
>65
53
<55
55-60
>60
<60
60-65
>65
54
<55
55-61
>61
<60
60-66
>66
55
<56
56-61
>61
<61
61-66
>66
56
<56
56-62
>62
<61
61-67
>67
57
<57
57-62
>62
<62
62-67
>67
58
<57
57-62
>62
<62
62-67
>67
59
<58
58-63
>63
<63
63-68
>68
60
<58
58-63
>63
<63
63-68
>68
61
<59
59-64
>64
<64
64-69
>69
62
<59
59-64
>64
<64
64-69
>69
63
<60
60-65
>65
<65
65-70
>70
64
<61
61-65
>65
<66
66-70
>70
65
<61
61-66
>66
<66
66-71
>71
66
<62
62-67
>67
<67
67-72
>72
67
<63
63-67
>67
<68
68-72
>72
68
<63
63-68
>68
<68
68-73
>73
69
<64
64-69
>69
<69
69-74
>74
70
<65
65-69
>69
<70
70-74
>74
71
<66
66-70
>70
<71
71-75
>75
72
<66
66-71
>71
<71
71-76
>76
73
<66
66-71
>71
<71
71-76
>76
74
<66
66-72
>72
<71
71-77
>77
75
<66
66-73
>73
<71
71-78
>78
76
<66
66-74
>74
<71
71-79
>79
77
<66
66-74
>74
<71
71-79
>79
>77
<66
66-75
>75
<71
71-80
>80
Option B: Cumulative Noise Impact Criteria Presentation
The impact criteria presentation for evaluating existing noise to project noise
cumulatively is presented in this option.
In certain cases, the cumulative form of the noise criteria shown in Figure 4-3
can be used. These cases involve projects where changes are proposed to an
existing transit system, as opposed to a new project in an area previously
without transit. Such changes might include operations of a new type of vehicle,
modifications of track alignments within existing transit corridors, or changes in
facilities that dominate existing noise levels. In these cases, the existing noise
FEDERAL TRANSIT ADMINISTRATION 28
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
sources change because of the project, and so it is not possible to define project
noise separately from existing noise. An example would be a commuter rail
corridor where the existing noise along the alignment is dominated by diesel
locomotive-hauled trains, and where the project involves electrification with the
resulting replacement of some of the diesel-powered locomotives with electric
trains operating at increased frequency of service and higher speeds on the
same tracks. In this case, the existing noise can be determined and a new future
noise can be calculated, but it is not possible to describe what constitutes the
“project noise.” For example, if the existing noise dominated by trains was
measured to be an L
dn
of 63 dBA at a particular location, and the new
combination of diesel and electric trains is projected to be an L
dn
of 65 dBA, the
change in the noise exposure due to the project would be 2 dB. Referring to
Figure 4-3, a 2-dB increase with an existing noise exposure of 63 dBA would be
rated as a moderate impact. Normally the project noise is added to the existing
noise to come up with a new cumulative noise, but in this case, the existing
noise was dominated by a source that changed due to the project, so it would
be incorrect to add the project noise to the existing noise. Consequently, the
existing noise determined by measurement is compared with a new calculated
future noise, but a description of what constitutes the actual project is complex.
Another example would be a rail corridor where a track is added and grade
crossings are closed, potentially resulting in a change in train location and horn
operation. Here the “project noise” results from moving some trains closer to
some receivers, away from others, and elimination of horns. In this case, the
change in noise level is more readily determined than the noise from the actual
project elements. In all cases, Figures 4-3 and 4-4 for changes in a transit system
results in the same assessment of impact as Figure 4-2 for development of
transit facilities in a new area.
The noise impact criteria in Figure 4-3 and Figure 4-4 are presented as an
increase in cumulative noise level between the existing and project conditions.
The horizontal axis represents the existing noise exposure and the vertical axis
is the increase in cumulative noise level due to the transit project. Note that
noise exposure is expressed as
L
eq(1hr)
for category 1 and 3 land uses and L
dn
for
category 2 land use. Since
L
eq(1hr)
and L
dn
are measures of total acoustic energy,
any new noise sources in a community will cause an increase, even if the new
source level is the same or less than the existing noise level (refer to decibel
addition in Appendix B). As shown in Figure 4-3, the criterion for moderate
impact is a noise exposure increase of 10 dB for an existing noise exposure level
of 42 dBA or less, but only a 1-dB increase when the existing noise exposure is
70 dBA.
As the existing level of ambient noise increases, the allowable level of transit
noise increases, but the total amount that community noise exposure is allowed
to increase is reduced. This accounts for the unexpected result that a project
exposure which is less than the existing noise exposure can still cause impact.
This is clearer from the examples listed in Table 4-6 which indicate the level of
transit noise allowed for different existing levels of exposure. Any increase
greater than shown in the table will cause moderate impact.
FEDERAL TRANSIT ADMINISTRATION 29
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Figure 4-3 Increase in Cumulative Noise Levels Allowed by Criteria
(Land Use Cat. 1 & 2)
Figure 4-4 Increase in Cumulative Noise Levels Allowed by Criteria
(Land Use Cat. 3)
This table shows that as the existing noise exposure increases from 45 dBA to
75 dBA, the allowed project noise exposure increases from 51 dBA to 65 dBA.
However, the allowed increase in the cumulative noise level decreases from 7
dB to 0 dB (rounded to the nearest whole decibel). The justification for this is
that people already exposed to high levels of noise should be expected to
tolerate only a small increase in the amount of noise in their community. In
contrast, if the existing noise levels are quite low, it is reasonable to allow a
greater change in the community noise for the equivalent difference in
annoyance.
FEDERAL TRANSIT ADMINISTRATION 30
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Note that Table 4-6 was developed for illustrative purposes and the official
criteria are included in Figure 4-3 and Figure 4-4 and the associated equations.
Table 4-6 Noise Impact Criteria: Effect on Cumulative Noise Exposure
L
dn
or L
eq(1hr)
in dBA (rounded to nearest whole decibel)
Existing
Noise
Exposure
Allowable Project
Noise Exposure
Before Moderate
Impact
Allowable
Combined Total
Noise Exposure
Allowable Noise
Exposure
Increase Before
Moderate Impact
45
51
52
7
50
53
55
5
55
55
58
3
60
57
62
2
65
60
66
1
70
64
71
1
75
65
75
0
4.2 Determine Noise Analysis Level
There are three levels of analysis to evaluate noise on a transit project based on
the type and scale of the project, stage of project development, and
environmental setting. These levels, described below, are the Noise Screening
Procedure, the General Noise Assessment and the Detailed Noise Analysis.
The Noise Screening Procedure, conducted first, defines the study area of any
subsequent noise impact assessment. Where there is potential for noise impact,
the General Noise Assessment and Detailed Noise Analysis procedures are
used to determine the extent and severity of impact. In some cases, a General
Noise Assessment may be all that is needed. However, if the proposed project
is near noise-sensitive land uses, and it appears at the outset that the impact
would be substantial, it is prudent to conduct a Detailed Noise Analysis.
Conduct the noise screening procedure and then determine the appropriate noise
analysis option.
Noise Screening Procedure – The Noise Screening Procedure is a simplified
method of identifying study area receivers or locations where a project may
have the potential for noise impacts from transit projects. This procedure
accounts for impact criteria, the type of project, and noise-sensitive land uses. If
no noise-sensitive land uses or receivers are present in the analysis area, then
no further noise assessment is needed. If noise-sensitive receivers are identified,
then proceed to conduct a General Assessment and/or a Detailed Assessment.
The Noise Screening Procedure steps are provided in Section 4.3.
General Noise Assessment – The General Noise Assessment is used to
examine potentially impacted areas identified in the screening step by examining
the location and estimated severity of noise impacts. This procedure considers
noise source and land use information likely to be available at an early stage in
the project development process. Estimates are made of project noise levels
and of existing noise conditions to model the location of a noise impact contour
FEDERAL TRANSIT ADMINISTRATION 31
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
that defines the outer limit of an impact corridor or area. This modeling method
uses transit-specific noise and adjustment data (in tabular and graphical form) for
the noise computations.
For many smaller projects, this assessment may be sufficient to define impacts
and determine whether noise mitigation is necessary. The procedure can be
used in conjunction with established highway noise prediction procedures to
compare highway, transit, and multimodal alternatives. If an assessment is
needed to inform the decision on transit mode and general alignment in a
corridor, the General Noise Assessment procedures should be used, and not
the Detailed Noise Analysis, which requires more detailed information.
The General Noise Assessment procedure is provided in Section 4.4. FTA has
also developed an Excel spreadsheet to more simply conduct the General Noise
Assessment. It is on FTA’s website at http://www.fta.dot.gov/12347_2233.html.
Detailed Noise Analysis – The Detailed Noise Analysis procedure is a
comprehensive assessment method that produces the most accurate estimates
of noise impacts for a proposed project. It is important to recognize that use of
the Detailed Noise Analysis methods will not provide more accurate results
than the General Noise Assessment unless more detailed and case-specific input
data are used.
The project must be defined to the extent that location, alignment, transit
mode, hourly operational schedules during day and night, speed profiles, plan
and profiles of guideways, locations of access roads, and landform topography
(including terrain and building features) are determined. A detailed Noise
Analysis is often accomplished at the development of the final environmental
impact statement (FEIS), record of decision (ROD), or combined FEIS/ROD in
the NEPA process, when the preferred alternative is undergoing refinements to
mitigate its adverse impacts. However, these project details may not be available
until the final design phase, requiring that the detail noise analysis be conducted
after the NEPA process is complete. However, it is recommended that the
detailed analysis be conducted earlier for controversial projects or projects with
highly noise-sensitive sites close to tracks.
A Detailed Noise Analysis may be warranted as part of the development of an
environmental assessment (EA) if there are potentially severe impacts due to
the proximity of noise-sensitive land uses.
In some cases, decisions on appropriate noise mitigation measures can be made
based on the results of the General Noise Assessment. But if costly measures
may be needed, it is generally recommended that a Detailed Noise Analysis be
conducted to verify the need and design of the noise mitigation. The Detailed
Noise Analysis is always appropriate under two sets of circumstances:
For a major transit project with likely noise impacts after the preferred
alternative has been selected.
For any other transit project where potentially severe impacts are
identified at an early stage.
FEDERAL TRANSIT ADMINISTRATION 32
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Noise impacts may occur for relatively minor transit projects when the project
is near noise-sensitive sites, particularly residences. In this case, completing a
Detailed Noise Analysis is recommended. Some examples include:
A terminal or station sited adjacent to a residential neighborhood
A maintenance facility located near a school
A storage yard adjacent to residences
An electric substation located adjacent to a hospital
The Detailed Noise Analysis procedure is provided in Section 4.5.
4.3 Evaluate Impact: Noise Screening Procedure
Identify the potential for impact using the Noise Screening Procedure described below.
Step 1: Identify Project Type
Identify the project type using Table 4-7 and confirm the assumptions in Table 4-8
are appropriate for the project.
The noise screening procedure is intended to be conservative to broadly
capture the potential for impact with minimal effort. To make the procedure
conservative, the project system must be assumed to be operating under
relatively high-capacity conditions, which would produce more noise than
normal operating conditions. In addition, the assumptions in Table 4-8 were
made using the lowest threshold of impact (50 dBA) from the criteria curves in
Figure 4-2. Clarification can be obtained from FTA on special cases that are not
represented in this section.
If the assumptions in Table 4-8 are not appropriate for the project, make
adjustments to the screening distances in Table 4-8 according to the
methodology in Section 4.4 or the FTA spreadsheet model.
Step 2: Determine the Screening Distance
Determine the appropriate screening distance considering the type of project and
shielding from intervening buildings.
2a. Determine the appropriate screening distance column in Table 4-7.
Option A: Buildings in the Sound Paths – Use the screening distances
in the “Intervening Buildings” column.
Option B: Buildings Not in the Sound Paths – Use the distances in
the “Unobstructed” column.
2b. Adjust these distances according to the methodology in Section 4.4, or the
FTA spreadsheet model, if the assumptions in Table 4-8 are not appropriate for
the project. The appropriate screening distance is where the project noise
reaches 50 dBA for the appropriate metric. If the assumptions in Table 4-8 are
not appropriate for a commuter rail grade crossing project where horns and
FEDERAL TRANSIT ADMINISTRATION 33
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
warning bells are used, use the FRA horn noise model available from the FRA
website to develop the screening distance distance (49 CFR § 222).
(
21
)
Step 3: Identify Study Area
Apply the screening distances as follows to identify the study area. The study area is
intended to be sufficiently large to encompass all potentially impacted locations.
Option A: Fixed Guideway Transit Sources – Apply the screening distance
from the guideway centerline.
Option B: Highway/Transit Sources (e.g., Bus) – Apply the screening
distance from the nearest ROW line on both sides of a highway or access road.
Option C: Small Stationary Facilities – Apply the screening distance from
the center of the noise-generating activity.
Option D: Stationary Facility Spread Over a Large Area – Apply the
screening distance from the outer boundary of the proposed project site.
Step 4: Locate Noise-Sensitive Land Uses
Locate all noise-sensitive land uses within the study area using Table 4-3.
See Section 4.1 for more information on noise-sensitive land uses. Include all
categories of noise-sensitive land uses in this step.
If no noise-sensitive land uses are identified, no further noise analysis is
needed. If one or more of the noise-sensitive land uses are in the study
area, proceed to Section 4.4 and complete a General Noise Assessment.
FEDERAL TRANSIT ADMINISTRATION 34
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Table 4-7 Screening Distance for Noise Assessments
Project Systems
Screening Distance, ft*
Unobstructed
Intervening Buildings
Fixed-Guideway Systems
Commuter Rail Mainline
750
375
Commuter Rail Station
With Horn Blowing
1,600
1,200
Without Horn Blowing
250
200
Commuter Rail Road Crossing with Horns and Bells
1,600
1,200
RRT
700
350
RRT Station
200
100
LRT
350
175
Streetcar
200
100
Access Roads to Stations
100
50
Low and Intermediate
Capacity Transit
Steel Wheel
125
50
Rubber Tire
90
40
Monorail
175
70
Yards and Shops
1000
650
Parking Facilities
125
75
Access Roads to Parking
100
50
Ancillary Facilities: Ventilation Shafts
200
100
Ancillary Facilities: Power Substations
250
125
Bus Systems
Busway
500
250
Bus Rapid Transit (BRT) on exclusive roadway
200
100
Bus Facilities
Access Roads
100
50
Transit Mall
225
150
Transit Center
225
150
Storage & Maintenance
350
225
Park & Ride Lots w/Buses
225
150
Ferry Boat Terminals
300
150
*Measured from centerline of guideway for fixed-guideway sources, from the ROW on both sides of the roadway for
highway/transit sources, from the center of noise-generating activity for stationary sources, or from the outer boundary
of the proposed project site for fixed facilities spread out over a large area.
FEDERAL TRANSIT ADMINISTRATION 35
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Table 4-8 Assumptions for Screening Distances for Noise Assessments
Type of Project
Operations
Speeds*
Metric**
Fixed-Guideway Systems
Commuter Rail Mainline
66 day /12 night; 1 loco, 6 cars
55 mph
L
dn
Commuter Rail
Station
With Horn Blowing
22 day / 4 night
N/A
L
dn
Without Horn Blowing
22 day / 4 night
N/A
L
dn
Commuter Rail-Highway Crossing with Horns
and Bells
22 day / 4 night
55 mph
L
dn
RRT
220 day / 24 night; 6-car trains
50 mph
L
dn
RRT Station
220 day / 24 night
20 mph
L
dn
LRT
150 day / 18 night; 2 artic veh.
35 mph
L
dn
Streetcar
150 day / 18 night
25 mph
L
dn
Access Roads to Stations
1000 cars, 12 buses
35 mph
L
eq(1hr)
Low and
Intermediate
Capacity Transit
Steel Wheel
220 day / 24 night
30 mph
L
dn
Rubber Tire
220 day / 24 night
30 mph
L
dn
Monorail
220 day / 24 night
30 mph
L
dn
Yards and Shops
20 train movements
N/A
L
eq(1hr)
Parking Facilities
1000 cars
N/A
L
eq(1hr)
Access Roads to Parking
1000 cars
35 mph
L
eq(1hr)
Ancillary Facilities: Ventilation Shafts
Rapid Transit in Subway
50 mph
L
dn
Ancillary Facilities: Power Substations
Sealed shed, air conditioned
N / A
L
dn
Bus Systems
Busway
30 buses, 120 automobiles
50 mph
L
eq(1hr)
BRT on exclusive roadway
30 buses
35 mph
L
eq(1hr)
Bus Facilities
Access Roads
1000 cars
35 mph
L
eq(1hr)
Transit Mall
20 buses
N/A
L
eq(1hr)
Transit Center
20 buses
N/A
L
eq(1hr)
Storage & Maintenance
30 buses
N/A
L
eq(1hr)
Park & Ride Lots
w/Buses
1000 cars, 12 buses
N/A
L
eq(1hr)
Ferry Boat Terminals
8 boats with horns used in
normal docking cycle
N/A
L
eq(1hr)
*N/A = not applicable
**L
eq(1hr)
= the loudest hour of project related activity during hours of noise sensitivity.
FEDERAL TRANSIT ADMINISTRATION 36
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
4.4 Evaluate Impact: General Noise Assessment
The General Noise Assessment should be completed after the Noise Screening
Procedure (Section 4.3), through which noise-sensitive receivers have been
identified. This can be completed either by using the General Noise Assessment
Procedure described below or using the FTA General Noise Assessment
Spreadsheet found on the following FTA website:
http://www.fta.dot.gov/12347_2233.html.
Assumptions are used throughout the General Noise Assessment. If the listed
assumptions are not appropriate for the project and good engineering
judgement cannot be used by following the General Noise Assessment
procedure, proceed to a Detailed Noise Analysis or consult with the FTA
Regional office.
Major steps in the General Noise Assessment procedure and recommended
workflow are shown in Figure 4-5 and listed below. Four examples of General
Noise Assessments are given at the end of this section. Many of these concepts
are explained in greater detail in the context of a Detailed Noise Analysis in
Section 4.5.
Step 1: Identify Noise-Sensitive Receivers – Identify noise-sensitive
receivers (Section 4.3) and their proximity to the project and major noise
sources.
Step 2: Determine Project Noise Source Reference Levels – Determine
the project noise sources and reference levels. Then, estimate the project noise
exposure at the reference distance of 50 ft considering operational
characteristics with preliminary estimations of the effect of mitigation.
Step 3: Estimate Project Noise Exposure by Distance – Estimate project
noise exposure at distances beyond 50 ft considering propagation characteristics
using a simplified procedure.
Step 4: Combine Noise Exposure from All Sources – Combine all
sources associated with the project to predict the total project noise at the
receivers.
Step 5: Measure Existing Noise Exposure – Measure the existing noise or
estimate the existing noise exposure using a simplified procedure.
Step 6: Inventory Impacts
Option A: Tabulate the change in noise (existing vs. estimated project
noise) at each noise-sensitive receiver or cluster, identifying all moderate
and severe impacts.
Option B: Take inventory of noise-sensitive receivers that fall within the
moderate and severe noise contours.
FEDERAL TRANSIT ADMINISTRATION 37
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Step 7: Determine Noise Mitigation Needs – Evaluate the need for
mitigation and repeat the General Noise Assessment with proposed mitigation.
Existing Noise
Exposure
Location of
Noise-Sensitive
Sites
Figure 4-5 Procedure for General Noise Assessment
Step 1: Identify Noise-Sensitive Receivers
Determine the proximity of noise-sensitive land uses identified in Section 4.3 to the
project and to the nearest major roadways and railroad lines.
1a. When necessary, use windshield surveys or detailed land use maps to
confirm the location of noise-sensitive land uses.
1b. For land uses more than 1,000 ft from major roadways or railroad
mainlines, obtain an estimate of the population density in the immediate
area, expressed in people per square mile. Distances to roadways or
railroads, or population density, will be used later to estimate the existing
FEDERAL TRANSIT ADMINISTRATION 38
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
noise level. Coordinate with the Metropolitan Planning Organization (MPO)
for population densities at an appropriate level of detail.
Step 2: Determine Project Noise Source Reference Levels
Determine the general source reference level for each project noise source.
Classify all project noise sources as fixed-guideway transit, highway/transit, or
stationary facility and determine the source reference levels. Note that a major
fixed-guideway system will have stationary facilities associated with it and that a
stationary facility may have highway/transit elements associated with it.
Option A: Fixed-guideway Transit Sources – For this manual, fixed-
guideway transit sources include commuter rail, RRT, LRT, streetcar, AGT,
monorail, and magnetically levitated vehicles (maglev). For commuter railroads
and LRT systems, the crossing of streets and highways at-grade is likely, and in
that case, warning devices should be included in the assessment. At an early
project stage, the information available for a General Noise Assessment
includes:
Candidate transit mo
de
Guidew
ay opt
ions
T
ime of operati
on
O
perational headway
s
Design speed
A
lternative alignment
s
T
his information is not sufficient to predict noise levels at all locations along the
ROW. Therefore, use conservative estimates (e.g., maximum (expected) design
speeds and operations at design capacities) to estimate worst-case noise levels.
First choose the appropriate fixed-guideway transit source reference level and
then predict the noise exposure at 50 ft in terms of L
eq(1hr)
and L
dn
.
A.i. Choose the reference source noise levels 50 ft from the track for
one
v
ehicle in terms of Sound Exposure Level (SEL) using Table 4-9. See Appendix
B
for a
detailed explanation of SEL. Note that the SEL reference speed is 50 mph
,
unles
s otherwise noted
.
FEDERAL TRANSIT ADMINISTRATION 39
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Table 4-9 Reference SEL's 50 ft from Track and at 50 mph, One Vehicle
Source
Type
Reference Conditions
Reference
SEL (SEL
ref
),
dBA
Commuter
Rail, At-Grade
Locomotives
Diesel-electric, 3000 hp, throttle 5
92
Electric
90
Diesel Multiple Unit (DMU)
Diesel-powered, 1200 hp
85
Horns
Within ¼ mile of grade crossing
110
Cars
Ballast, welded rail
82
Rail Transit and Streetcars at 50 mph
At-grade, ballast, welded rail
82
Rail Transit and Streetcars at 25 mph
At-grade, ballast, welded rail
76
Transit whistles / warning devices
Within 1/8 mile of grade crossing
93
AGT
Steel Wheel
Aerial, concrete, welded rail
80
Rubber Tire
Aerial, concrete guideway
78
Monorail
Aerial straddle beam
82
Maglev
Aerial, open guideway
72
A.ii. Collect the following data:
Number
of train passbys during the day (7 a.m. to 10 p.m.) and night (
10
p.m. to 7 a.m.) for category 2 land uses
Maxi
mum number of train passbys during hours that category 1
or
category 3 land uses are normally in use (typically the peak hour train
volume)
Number
of vehicles per train for each time period for category 2 lan
d
us
es (if this number varies during the day or night, take the average
)
Maxi
mum number of vehicles per train during hours that category 1
or
c
ategory 3 land uses are normally in use (typically the peak hour tra
in
volume)
T
rain speed in mph (maximum expected
)
Guideway configuration
Loca
tion of highway and street grade crossings, if a
ny
If this process is repeated to estimate the effect of proposed noise
mit
igation, include the noise barrier locat
ion
A.iii
. Calculate the noise exposure at 50 ft in terms of L
eq(1hr)
:
Ca
lculate L
eq(1hr)
for each source using the appropriate equations in
T
able 4-
10.
Compute L
eq(1hr).Combo
using Eq. 4-6. It may be necessary to compute the
c
ombined totals with and without warning horns. Some neighborhoo
ds
a
long the corridor may be exposed to horn noise, but some may not
.
A.iv. Ca
lculate the noise exposure at 50 ft in terms of L
dn
:
If the project noise will affect any residential receivers, calculate the L
dn
using the combined L
eq(1hr)
for both the daytime and nighttime periods
s
eparately, using the appropriate equations in Table 4-10
.
It may be necessary to calculate L
dn
with and without warning horns, as
in
the previous step
.
No
te that the equations in Table 4-10 include terms to account for a
difference in speed from the 50 mph reference speed and a numerical
adjustment to account for the one-hour time period for this metric. For
FEDERAL TRANSIT ADMINISTRATION 40
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
more information on the numerical adjustment to represent the time period
of interest, see Appendix B.1.4.4.
Table 4-10 presents an estimate of the noise reduction potentially provided by
wayside noise barriers that can be used when assessing mitigation options in a
General Noise Assessment. If impact is determined during the General Noise
Assessment, repeat the procedure and include proposed mitigation according to
Section 4.4, Step 7. See Section 4.5, Step 7 for a complete description of the
benefits resulting from various noise mitigation measures that can be evaluated
with a Detailed Noise Analysis.
FEDERAL TRANSIT ADMINISTRATION 41
Table 4-10 Computation of Noise Exposure at 50 ft for Fixed-Guideway General Noise Assessment
Locomotives
*
L
eq(1hr)
at 50 ft
Eq. 4-1
Locomotive
Warning
Horns**
L
eq(1hr)
at 50 ft
Eq. 4-2
Rail Vehicles
†
L
eq(1hr)
at 50 ft
Eq. 4-3
Streetcars
(25 mph or
slower)
L
eq(1hr)
at 50 ft
Eq. 4-4
Transit
Warning Horns
L
eq(1hr)
at 50 ft
Eq. 4-5
Combined
Locomotive and
transit
††
L
eq(1hr)
at 50 ft
Eq. 4-6
Daytime
L
d
at 50 ft
where V = V
d
, N
Loco
= N
d
(loco events), and N
Cars
= N
d
(car events)
Eq. 4-7
Nighttime
L
n
at 50 ft
where V = V
n
, N
Loco
= N
d
(loco events), and N
Cars
= N
d
(car events)
Eq. 4-8
Day/Night
L
dn
at 50 ft
Eq. 4-9
= average number of locomotives per train
=
constant
-10 for passenger diesel
0 for DMUs
+10 for electric
S = train speed, mph
=
average hourly volume of train traffic, trains per hour
= average number of cars per train
= constant
+5 for jointed track or for a crossover within 300 ft
+4 for aerial structure with slab track (except AGT and monorail)
+3 for embedded track on grade
-5 if a noise barrier blocks the line of sight
V
d
= average hourly daytime volume of train traffic, V
n
= average hourly nighttime volume of train traffic,
trains per hour trains per hour
N
d
= average hourly number of events that occur N
n
= average hourly number of events that occur during
during daytime (7 a.m. to 10 p.m.) nighttime (10 p.m. to 7 a.m.)
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
* Assumes a diesel locomotive power rating at approximately 3000 hp.
** Based on FRA’s horn noise model (http://www.fra.dot.gov/eLib/Details/L04091).
† Includes all commuter rail cars, transit cars, streetcars above 25 mph, AGT and monorail.
† † Only include appropriate terms.
FEDERAL TRANSIT ADMINISTRATION 42
Source* Reference SEL, dBA
Automobiles and Vans 74
Buses (diesel-powered) 82
Buses (electric) 80
Buses (hybrid) 83**
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Option B: Highway/Transit Sources – The highway/transit type sources
include most transit modes that do not require a fixed-guideway. Examples are
high-occupancy vehicles, such as buses, commuter vanpools and carpools. Use
the instructions below to estimate source noise levels for projects that involve
these types of vehicles and are using FTA’s environmental review procedures.
At an early project stage, the information available for a General Noise
Assessment includes:
Vehicle type
Transitway design options
Time of operation
Typical headways
Design speed
Alternative alignments
This information is not sufficient to predict noise levels at all locations along the
ROW; therefore, use of conservative estimates (e.g., maximum (expected)
design speeds and operations at design capacities) to estimate worst-case noise
impact levels is recommended. The procedure is consistent with FHWA’s
highway noise prediction method. The reference SEL levels in Table 4-11
correspond to FHWA’s source emission levels and speed coefficients for buses
and automobiles.
(
22
)
B.i. Using Table 4-11, choose the appropriate reference source noise levels 50
ft from the roadway in terms of SEL. Note that the SEL reference speed is 50
mph, unless otherwise noted.
Table 4-11 Source Reference Levels at 50 ft from Roadway, 50 mph
* Assumes normal roadway surface conditions.
** For hybrid buses, determine Reference SEL on a
case-by-case basis because they vary, and data are
scarce.
B.ii. Collect the following data:
Number of vehicle passbys during the day (7 a.m. to 10 p.m.) and night
(10 p.m. to 7 a.m.) for each vehicle type in Table 4-11, if a category 2
land use is present
Number of vehicle passbys during hours that category 1 or category 3
land uses are normally in use, each vehicle type in Table 4-11
Speed (maximum expected)
Transitway configuration (with or without noise barrier)
B.iii. Calculate the noise exposure at 50 ft in terms of L
eq(1hr)
. Calculate L
eq(1hr)
for each source using the appropriate equations in Table 4-12.
FEDERAL TRANSIT ADMINISTRATION 43
Table 4-12 Computation of L
eq(1hr)
and L
dn
at 50 ft for Highway/Transit General Noise Assessment
L
eq(1hr)
at 50 ft
Eq. 4-10
Daytime
L
d
at 50 ft
where V = V
d
Eq. 4-11
Nighttime
L
n
at 50 ft
where V = V
n
Eq. 4-12
L
dn
at 50 ft
Eq. 4-13
Barrier
Adjustment
= -5 for noise barriers
S
V
d
V
n
= hourly volume of vehicles, vehicles per hour
= Speed constant
15 for diesel buses
28 for electric buses
(23)
21 for hybrid buses
30 for automobile and van pools
= average vehicle speed, mph
= average hourly daytime volume of vehicles, vehicles per hour
= average hourly nighttime volume of vehicles, vehicles per hour
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
B.iv. Calculate the noise exposure at 50 ft in terms of L
dn
. If the project noise
will affect any residential receivers, calculate the L
dn
using the combined L
eq(1hr)
for both the daytime and nighttime periods separately, using the appropriate
equations in Table 4-12.
Note that the equations in Table 4-12 include terms to account for a speed
other than the 50 mph reference speed and a numerical adjustment to account
for the one-hour time period for this metric. For more information on the
numerical adjustment to represent the time period of interest, see Appendix
B.1.4.4.
Table 4-12 presents an estimate of noise reduction potentially provided by
wayside noise barriers. This is considered illustrative given that barriers are the
most common noise mitigation measure. See Section 4.5, Step 7 for a complete
description of the benefits resulting from noise mitigation. If impact is
determined during the General Noise Assessment without mitigation, repeat
the procedure and include proposed mitigation.
Option C: Stationary Sources – Stat
ionary sources include fixed transit
system facilities. New transit facilities undergo a site review for best location
that considers the noise sensitivity of surrounding land uses. Although many
facilities such as bus maintenance garages are usually located in industrial and
commercial areas, some facilities such as bus terminals, ferry terminals, train
stations, and park-and-ride lots may be placed near residential neighborhoods
where noise impact may occur. Access roads to some of these facilities may also
FEDERAL TRANSIT ADMINISTRATION 44
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
pass through noise-sensitive areas. Noise from access roads is treated according
to the procedures described in the Highway/Transit Sources category. In a
General Noise Assessment, only the prominent features of each fixed facility are
considered in the noise analysis.
C.i. For small facilities, using Table 4-13, determine the reference source nois
e
lev
els 50 ft from the center of the site in terms of SEL. The source referenc
e
lev
els given in the table are based on measurements for the peak hour
of
oper
ation of a typical stationary source of the noted type and siz
e.
A large facility, such as a rail yard, is spread out over considerable area with
various noise sources with different noise levels depending on the layout of the
facility. Specifying a single reference SEL for the facility at 50 ft from the center
of the site could be misleading if all of these different noise sources are not
represented. Therefore, the reference distance should be the equivalent
distance of 50 ft, which is determined by estimating the noise levels from the
center of the site at a distance far enough to capture all noise sources and
projecting back to 50 ft from the center of the site. This approach allows for a
conservative estimate of noise for all surrounding areas and the equivalent noise
can be considered as concentrated at the center of the site. If the location of
noise sources is known, then the distance should be taken from the point of the
noisiest activity on the site (e.g., the dock in the case of ferry boat operations)
instead of the center of the site.
Table 4-13 Source Reference Levels at 50 ft from Center of Site, Stationary Sources
Source
Reference
SEL, dBA
Reference Conditions
Rail System
Yards and shops
118
20 train movements in peak activity hour
Layover tracks (commuter rail)
109
1 train with diesel locomotive idling for 1 hour
Crossing signals
109
3600 second duration
Bus System
Storage yard
111
100 buses accessing facility in peak activity hour
Operating facility
114
100 buses accessing facility, 30 buses serviced and
cleaned in peak activity hour
Transit center
101
20 buses in peak activity hour
Ferry Terminal
Ferry boat (no fog horn sounded)
97
4 ferry boat landings in 1 hour
Ferry boat (fog horn sounded)
100
Parking Garage
92
1000-car capacity in peak activity hour
Park & Ride Lot
101
12 buses, 1000 cars in peak activity hour
C.ii. Collect the following data:
Number
of layover tracks and hours of us
e
Number
of buses, if different from assumed reference conditions (if t
his
number
varies during the day or night, take the averag
e)
Number of ferry boat landings, if different from assumed reference
c
onditions (if this number varies during the day or night, take t
he
average)
A
ctual capacity of parking garage
or lot
FEDERAL TRANSIT ADMINISTRATION 45
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
C.iii. Calculate L
eq(1hr)
at 50 ft. Calculate L
eq(1hr)
for each source using the
appropriate equations in Table 4-14.
C.iv. Calculate L
dn
at 50 ft. If the project noise will affect any residential
receivers, calculate the L
dn
using the combined L
eq(1hr)
for both the daytime and
nighttime periods separately, using the appropriate equations in Table 4-14.
The equations in Table 4-14 include a numerical adjustment to account for the
one-hour time period for this metric. See Appendix B.1.4.4 for more
information on the numerical adjustment.
Table 4-14 presents an estimate of noise reduction potentially provided by noise
barriers at the property line. Only approximate locations and lengths for barrier
or other noise mitigation measures are developed during a General Noise
Assessment to provide a preliminary indication of the costs and benefits of
mitigation. A Detailed Noise Analysis of the preferred alternative is usually
warranted following the General Noise Assessment (if it predicts any impacts)
to verify impacts and design the mitigation.
FEDERAL TRANSIT ADMINISTRATION 46
Table 4-14 Computation of L
eq(1hr)
and L
dn
at 50 ft for Stationary Source General Noise Assessment*
L
eq(1hr)
at 50 ft
Eq. 4-14
Daytime
L
d
at 50 ft
Eq. 4-15
Nighttime
L
n
at 50 ft
Eq. 4-16
L
dn
at 50 ft
Eq. 4-17
Barrier
Adjustment
= -5 for noise barrier at property line
Volume
=
Adjustment
= )
Rail yards and shops
=
Layover tracks
=
Bus storage yard
=
Bus operating facility
=
Bus transit center
=
Ferry terminal
=
Parking garage
Park & ride lot
=
=
Crossing signals
= average number of trains per hour during the day (7AM to 10PM) or night
(1
0PM to 7AM)
= average number of buses per hour during the day or night
= average number of ferry boat landings per hour during the day or night
= average number of buses serviced and cleaned per hour during the day or night
= average number of automobiles per hour during the day or night
E
= average hourly duration of events, sec during the day or night
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
* If any of these numbers is zero, omit that term.
FEDERAL TRANSIT ADMINISTRATION 47
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Step 3: Estimate Project Noise Exposure by Distance
Estimate the project noise exposure for locations beyond the reference distance, such
as for noise-sensitive land uses.
In the previous step, noise exposure at the reference distance of 50 ft was
calculated for the various noise sources. This step describes how to estimate
the project noise exposure beyond (or, if needed, closer than) the reference
distance, such as at noise-sensitive land uses locations. This procedure estimates
the source’s noise exposure as a function of distance. Adjustments are provided
to account for shielding attenuation from rows of buildings.
3a. Select the appropriate distance correction curve (Fixed-Guideway &
Highway or Stationary) from Figure 4-6. The Fixed-Guideway & Highway curve
refers to line sources while the Stationary curve is refers to point sources. The
distance correction factor (C
distance
) is 0 dB at 50 ft.
3b. Choose a distance other than 50 ft, such as the distance to a receiver.
Determine the correction factor using Figure 4-6 or calculate using the
equations in Table 4-15.
(
iii
)
For distances beyond 1,000 ft, the equations in Table
4-15 can be used; however, ground effects have an upper limit and atmospher
ic
conditions may affect propagation characteristics. More detailed calculation
met
hods may be required to account for those effects beyond 1,000 ft
.
Figure 4-6 Curves for Estimating Exposure vs. Distance in General Noise Assessment
iii
Note that the curves and equations assume acoustically soft ground beyond a distance of 50 ft. See Table 4-27
for more detailed calculation of ground attenuation.
FEDERAL TRANSIT ADMINISTRATION 48
Table 4-15 Distance Correction Factor Equations for General Noise Assessment
Source Equation
Stationary Sources
Eq. 4-18
Fixed-guideway and Highway
Eq. 4-19
distance, ft
where:
=
or
at the new distance in feet
=
or
at 50 ft
Table 4-16 Computing Total Noise Exposure
Total L
eq(t)
from all sources
for the hour of interest:
)
Eq. 4-21
Total L
dn
from all sources
)
Eq. 4-22
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
3c. Apply the distance correction (C
distance
) to the project noise exposure at 50
ft (Section 4.4, Step 2) using the following equation:
Eq. 4-20
3d. Repeat Step 3c for each source-receiver distance from the project. A noise
exposure vs. distance curve can be created, if desired, by calculating the noise
exposure for all distances of interest and plotting a curve. This curve can be
used to assist in determining the noise impact contour for the first row of
unobstructed buildings. This plot can be used to display noise from both
unmitigated and mitigated conditions to assess the potential benefits from
mitigation measures.
For second row receivers and beyond, it is necessary to account for shielding
attenuation from rows of intervening buildings. Without accounting for
shielding, impacts may be substantially overestimated. Use the following general
rules to account for the effect of shielding from intervening rows of buildings:
Assign 4.5 dB of shielding attenuation for the first row of intervening
buildings only.
Assign 1.5 dB of shielding attenuation for each subsequent row, up to a
maximum total attenuation of 10 dB.
Step 4: Combine Noise Exposure from All Sources
Combine all sources to predict the total project noise at the receivers using the
equations in Table 4-16, once propagation adjustments have been made for the noise
exposure from each source separately (fixed-guideway, highway/transit, and
stationary).
FEDERAL TRANSIT ADMINISTRATION 49
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Step 5: Estimate Existing Noise Exposure
Measure the existing noise or estimate the existing noise exposure using a simplified
procedure.
Existing noise in the project vicinity must be quantified and compared to the
project noise to determine the potential noise impact. It is generally
recommended to measure existing noise, especially at locations known to be
noise-sensitive, but if measurement results are not available then they must be
estimated. In the Detailed Noise Analysis, the existing noise exposure is usually
based on noise measurements at representative locations in the community.
It is not necessary or recommended that
Changes to Existing Transit
existing noise exposure be determined by
For projects that propose
measuring at every noise-sensitive
changes to an existing transit
location in the project area. Rather, the
system, such as a rehabilitation
recommended approach is to
project, the project noise can
characterize the noise environment for
include changes to the existing
"clusters" of sites based on measurements
noise because of the project,
or estimates at representative locations in
and so it is not possible to
the community. Because of the sensitivity
define project noise separately.
of the noise criteria to the existing noise
For these projects, refer to
exposure, careful characterization of pre-
Section 4.1, Step 3 – Option B,
project ambient noise is important.
on using the cumulative
Guidelines for selecting representative
noise criteria.
receiver locations and determining
ambient noise are provided in Appendix D and Appendix E, respectively.
This section describes how to estimate the existing noise in the project study
area from general data available early in project planning. The procedure uses
Table 4-17, where a neighborhood's existing noise exposure is based on
proximity to nearby major roadways or railroads, or on population density. For
areas near major airports, published aircraft noise contours can also be used to
estimate the existing noise exposure. The process is as follows:
5a. Obtain scaled mapping and aerial photographs showing the project location
and alternatives. A scale of 1 inch = 200 or 400 ft is convenient for the accuracy
needed in the noise assessment. The size of the base map should be sufficient to
show distances of at least 1000 ft from the center of the alignment or property
center, depending on whether the project is a line source (fixed guideway/
roadway) or a stationary facility. These data are commonly available from local
transit agencies and a number of publicly available online tools.
5b. Estimate the existing noise exposure by estimating the noise from major
roads and railroad lines or by population density. First, evaluate the site's
proximity to major roads and railroad lines including those that are included in
the project. If these noise sources are far enough away that ambient noise is
dominated by local streets and community activities, estimate the existing noise
based on population density. To choose the appropriate existing noise
exposure, compare noise levels from each of the three categories—Roadways,
Railroads, and Population Density—and select the lowest level. In case of a
FEDERAL TRANSIT ADMINISTRATION 50
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
lightly used railroad (one train per day or less) select the Population Density
category. Existing noise levels are presented in Table 4-17. Refer to Section 4.1,
Step 3 – Option B, on using the cumulative noise criteria for projects that
propose changes to an existing transit system, such as a rehabilitation project.
Option A: Roadways – Major roadways are separated into two categories for
a general noise assessment. Roadways that cannot be described by these two
categories are not considered major roadways and would use the Population
Density method described below. The roadway categories are as follows:
Interstate highway—roadways with 4 or more lanes that allow trucks
Other roadway—parkways without trucks and city streets with the
equiv
alent of 75 or more heavy trucks per hour or 300 or mor
e
medium
trucks per
hour
T
he estimated roadway noise levels in Table 4-17 are based on data for light to
moderate traffic on typical highways and parkways using FHWA highway noise
prediction procedures. Where a range of distances is given, the noise exposure
estimates are given at the larger distance (note that the traffic noise at the
smaller distance is underestimated). For highway noise, distances are measured
from the centerline of the near lane for roadways with two lanes, while for
roadways with more than two lanes the distance is measured from the
geometric mean of the roadway. This distance is computed as follows:
Eq. 4-23
where:
= distance to the geometric mean in feet
= distance to the nearest lane centerline in feet
= distance to the farthest lane centerline in feet
Option B: Railroad Lines – For railroads, the estimated noise levels are
based on an average train traffic volume of 5–10 trains per day at 30–40 mph for
main line railroad corridors and the noise levels are provided in terms of L
dn
only. Distances are referenced to the track centerline, or in the case of multiple
tracks, to the centerline of the rail corridor. Because of the intermittent nature
of train operations, train noise will affect the L
eq(1hr)
only during certain hours of
the day, and these hours may vary from day to day. Therefore, to avoid
underestimating noise impact when using L
eq(1hr)
, it is recommended that sites
near rail lines are estimated based on nearby roadways or population density
unless very specific train information is available.
Option C: Population Density – In areas away from major roadways, noise
from local streets or in neighborhoods is estimated using a relationship
determined during a research program by EPA.
(
24
)
EPA determined that ambient
noise can be related to population density in locations away from transportation
corridors, such as airports, major roads and railroad tracks, according to the
following relation:
Eq. 4-24
FEDERAL TRANSIT ADMINISTRATION 51
where:
= in dBA
= population density in people per square mile
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
In areas near major airports, published noise contours can be used to estimate
the existing noise exposure. The L
dn
from such contours should be applied if
greater than the estimates of existing noise from other sources at a given
location.
Table 4-17 Estimating Existing Noise Exposure for General Noise Assessment
Dominant
Existing Noise
Source
Distance from Major
Noise Source, ft*
Population
Density, people
per sq. mi.
Noise Exposure Estimates
L
eq
Day
L
eq
Evening
L
eq
Night
L
dn
10–50
75
70
65
75
50–100
70
65
60
70
Interstate
100–200
65
60
55
65
Highway**
200–400
60
55
50
60
400–800
55
50
45
55
800 and up
50
45
40
50
10–50
70
65
60
70
50–100
65
60
55
65
Other Roadway†
100–200
60
55
50
60
200–400
55
50
45
55
400 and up
50
45
40
50
10–30
--
--
--
75
30–60
--
--
--
70
60–120
--
--
--
65
Railway††
120–240
--
--
--
60
240–500
--
--
--
55
500–800
--
--
--
50
800 and up
--
--
--
45
1–100
35
30
25
35
100–300
40
35
30
40
300–1000
45
40
35
45
Population
1000–3000
50
45
40
50
3000–10000
55
50
45
55
10000–30000
60
55
50
60
30000 and up
65
60
55
65
* Distances do not include shielding from intervening rows of buildings. Generally, for estimating shielding
attenuation in populated areas, assume 1 row of buildings every 100 ft, 4.5 dB for the first row, and 1.5 dB for
every subsequent row up to a maximum of 10 dB attenuation.
** Roadways with 4 or more lanes that permit trucks, with traffic at 60 mph.
† Parkways with traffic at 55 mph, but without trucks, and city streets with the equivalent of 75 or more heavy
trucks per hour and 300 or more medium trucks per hour at 30 mph.
†† Main line railroad corridors typically carrying 5-10 trains per day at speeds of 30-40 mph.
Step 6: Inventory Noise Impacts
Inventory the potential noise impacts either by comparing the project and existing noise
at each noise-sensitive land use or by developing noise impact contours.
Use land use information and assumptions for shielding attenuation from rows
of buildings. In some cases, it may be necessary to supplement the land use
information or determine the number of dwelling units within a multi-family
building with a visual survey. If the objective is to compare major alignment
options, it may not be necessary to identify every different type of noise-
FEDERAL TRANSIT ADMINISTRATION 52
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
sensitive land use. The inventory may include a subset of land uses, including
residential and public institutional uses.
Option A is the preferred method as it quantifies the noise impact at each
noise-sensitive land use indicating the severity of the impact. Option B may be
useful for comparing and narrowing down major alignment options with
numerous noise-sensitive land uses.
Option A: Compare existing noise to project noise at each noise-
sensitive land use.
A1. Tabulate each individual noise-sensitive land use building and site within the
identified screening distance (Section 4.3).
A2. Determine for each noise-sensitive land use the existing noise (Section 4.4,
Step 5), the project noise (Section 4.4, Step 3) and the resulting change in noise.
A3. Designate each noise-sensitive land use with either a no, moderate, or
severe noise impact based on the criteria in Section 4.1.
A4. Identify all moderate and severe impacts on a project map.
Option B: Develop noise impact contours.
B1. Determine the noise level thresholds at which the project noise would
cause moderate and severe impacts using the estimated existing noise exposure
from Section 4.4, Step 5 and the noise impact criteria in Figure 4-2.
B2. Determine the distances from the project boundary to the two impact
levels using the noise exposure vs. distance curves or equations in Section 4.4,
Step 3.
B3. Plot points on a project land use map that correspond to the distances
determined in Section 4.4, Step 3. Continue this process for all areas
surrounding the project. Connect the plotted points to represent the noise
impact contours.
B4. Tabulate all noise-sensitive land use buildings and sites that lie between the
impact contours and the project boundary. For residential buildings, an estimate
of the number of dwelling units is satisfactory.
B5. Prepare summary tables showing the number of buildings (and estimated
dwelling units, if available) within both impact categories.
Specific decibel level noise contours, for example, 65 dBA, can also be plotted if
desired. The distances can be determined using the procedure in Section 4.4,
Step 3 by substituting the desired decibel level for the impact threshold.
Locations of points will change with respect to the project boundary as the
existing ambient exposure changes, the project source levels change, and as
shielding effects change. It is recommended to plot points close together to
FEDERAL TRANSIT ADMINISTRATION 53
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
draw a smooth curve. For a General Noise Assessment, the contours may be
drawn through buildings and terrain features as if they were not present. This
practice is acceptable considering the level of detail associated with a project in
its early stages of development. Example 4-1 and Example 4-4 describe the
development of noise contours with illustrations.
Step 7: Determine Noise Mitigation Needs
Apply estimates of the noise reduction from proposed mitigation measures (Section
4.4, Step 2), where the assessment shows either severe or moderate impact, and
repeat the tabulation of noise impacts.
Note that noise barriers are the only form of mitigation available in a General
Noise Assessment. The other mitigation measures are available for a Detailed
Noise Analysis. The approximate noise barrier lengths and locations developed
in a General Noise Assessment provide a preliminary basis for evaluating the
costs and benefits of impact mitigation. This evaluation will provide a
conservative estimate of the effect of the mitigation on the identified impacts.
In general, it is recommended to complete a Detailed Noise Analysis for final
mitigation measures. However, if impact is identified through a General Noise
Assessment and can be mitigated to a level of no impact using the noise
reduction estimates included in the General Noise Assessment, a Detailed
Noise Analysis may not be needed. Mitigation assumed in the assessment used
for the NEPA evaluation must be included in the project as a commitment.
Consult with the FTA Regional office to determine if a Detailed Noise Analysis
is required for final mitigation measures.
The following examples illustrate how to complete general noise assessments
for varying project types including commuter rail, highway/transit, BRT system,
and a transit center.
Example 4-1 General Noise Assessment – Commuter Rail
General Noise Assessment for a Commuter Rail System in an
Existing Abandoned Railroad Right-of-Way
The following example illustrates the General Noise Assessment procedure for a new fixed-guideway project.
The hypothetical project is a commuter rail system to be built within the abandoned ROW of a railroad. The
example covers a segment of the corridor that passes through a densely developed area with population density
of 25,000 people per square mile in mixed single- and multi-family residential land uses as shown in Figure 4-7.
The example is presented in two parts: first, a segment where the rail line is grade-separated and a horn is not
sounded; and second, an at-grade street-rail crossing where the horn is sounded.
Assumptions
Project Corridor
Existing population density is 25,000 people per square mile.
Commuter Rail System
Commuter train with one locomotive and a three-car consist on a double-track at-grade system with
welded rail. Trains operate with 20-minute headways during peak hours and 1-hour headways during
off-peak. Speeds are approximately 40 mph along the corridor.
FEDERAL TRANSIT ADMINISTRATION 54
Determine Project Source Reference Levels at 50 ft
Classify the noise source: Fixed-Guideway Transit
Determine noise source reference level from Table 4-9:
Locomotive: 92 dBA
Cars: 82 dBA
Estimate Project Noise Exposure at 50 ft
Determine average hourly daytime and nighttime volumes of train traffic.
Daytime (7 a.m. – 10 p.m.)
Nighttime (10 p.m. – 7 a.m.)
Use Eq. 4-1 and Eq. 4-3 to calculate the daytime L
eq(1hr)
at 50 ft for the locomotives and rail cars.
A at 50 ft
A at 50 ft
Calculate the total daytime L
d
for the locomotive and rail cars using Eq. 4-7.
at 50 ft
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Operating Schedule
Daytime
Nighttime
Headway (minutes)
Trains per hour
Period
Period
Inbound
Outbound
Inbound
Outbound
Total
Total
7 a.m. – 8 a.m.
20
20
3
3
6
6
8 a.m. – 4 p.m.
60
60
1
1
2
16
4 p.m. – 6 p.m.
20
20
3
3
6
12
6 p.m. – 10 p.m.
60
60
1
1
2
8
10 p.m. – 11 p.m.
60
60
1
1
2
2
11 p.m. – 5 a.m.
--
--
--
--
--
--
5 a.m. – 6 a.m.
60
60
1
1
2
2
6 a.m. – 7 a.m.
20
20
1
1
2
2
Part 1: Grade-Separated Street Crossing
FEDERAL TRANSIT ADMINISTRATION 55
Use Eq. 4-1 and Eq. 4-3 to calculate the daytime L
eq(1hr)
at 50 ft for the locomotives and rail cars.
A at 50 ft
A at 50 ft
Calculate the total daytime L
d
for the locomotive and rail cars using Eq. 4-7.
at 50 ft
Calculate the nighttime L
eq(1hr)
at 50 ft for the locomotives and rail cars.
at 50 ft
at 50 ft
Calculate the total nighttime L
n
for the locomotive and rail cars using Eq. 4-8.
at 50 ft
Calculate L
dn
at 50 ft for the project using Eq. 4-9.
at 50 ft
Existing
Noise
L
dn
Onset of Moderate
Impact
L
dn
Onset of Severe Impact
L
dn
60 dBA 58 dBA 64 Dba
above. The project noise level at 50 ft is approximately 64 dBA.
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Estimate Existing Noise Exposure
Estimate existing noise at noise-sensitive sites. Since the existing alignment is on an abandoned railroad, the
dominant existing noise source can be described by a generalized noise level to characterize a large area.
Use Table 4-17 and population density of 25,000 people per square mile to determine the existing noise
level. Unobstructed residences range from 100 to 200 ft from the rail line.
According to Table 4-17: L
dn
= 60 dBA
Determine Noise Level and Distance for the Onset Of Impact
Determine the noise level for the onset of moderate and severe impact using Figure 4-2 and the existing
noise level of 60 dBA. Note that this project is land use category 2 and the appropriate metric is L
dn
.
Determine the distance from the project noise sources to the noise impact contours using the fixed-
guideway curve in Figure 4-6 (or the equations in Table 4-15) and the project impact thresholds obtained
Moderate impact (58 dBA)
According to Figure 4-6, the distance correction is approximately -6 dB at 120 ft.
Severe Impact (64 dBA)
FEDERAL TRANSIT ADMINISTRATION 56
Noise Mitigation
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
According to Figure 4-6, the distance correction is less than 0 dB at approximately 51 ft.
Onset of Moderate Onset of Severe
Project Level
Impact Impact
L
dn
Distance Distance
64 dBA 120 ft 51 ft
Develop Noise Impact Contours
Draw contours for each affected land use, based on the above table and its distance from the rail line
(Figure 4-7). Note that the impact distances listed are in terms of distance to the centerline of the
Commuter Rail corridor.
Inventory of Noise Impact
There are six residential buildings within the contours defining moderate impact (shaded in Figure 4-7).
The procedure is repeated assuming a noise barrier to be placed at the railroad ROW line. The barrier
serves to reduce project noise from the commuter rail by at least 5 dB. Note that the barrier does not
affect the project criteria to be used in determining impact, and the same existing noise levels (as the case
without a barrier) are used to determine these thresholds.
In this example, the noise barrier decreases the distance to moderate impact from 120 to 60 ft and
eliminates all residential noise impact for this segment of the project area.
Figure 4-7 Noise Impacts of Hypothetical Commuter Rail
Part 2: At-Grade Crossing with Horn Blowing
Now consider the case of an active street crossing of the commuter railroad tracks. The General Noise
Assessment method includes source reference levels for horns on moving trains and warning bells (crossing
signals) at the street crossing. According to Table 4-9, the horn noise applies to track segments within ¼ mile of
the grade crossing.
Estimate Project Noise Exposure at 50 ft
Using the train volumes from Part 1 and the information in Table 4-9 and Table 4-10, determine the day
and nighttime L
eq(1hr)
from sounding the horns at 50 ft.
A
FEDERAL TRANSIT ADMINISTRATION 57
Project Level
L
dn
Onset of Moderate
Impact
Distance
Onset of Severe
Impact
Distance
64 dBA
120 ft
51 ft
Calculate the L
dn
at 50 ft from train horns using Eq. 4-9 :
-13.8
Calculate L
dn
at 50 ft. from the warning bells using Eq. 4-17:
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
At-grade street crossings will have warning bells, typically sounding for 20 seconds for every train passby.
The total daytime and nighttime durations are as follows:
= average daytime hourly duration
=20 seconds X 2.8 trains/hour = 56 seconds/hour
= average nighttime hourly duration
=20 seconds X 0.7 trains/hour = 14 seconds/hour
From Table 4-14:
-13.8
Compared to horn blowing, the crossing signal warning bell noise is negligible, but still must be included in the
evaluation.
Estimate Existing Noise Exposure
From Part 1, the existing noise level is 60 dBA.
Determine Noise Level and Distance for the Onset Of Impact
As in Part 1, the existing noise level (60 dBA) is used to determine the onset of moderate and severe
impacts:
Existing
Noise
L
dn
Onset of Moderate
Impact
L
dn
Onset of Severe Impact
L
dn
60 dBA
58 dBA
64 dBA
FEDERAL TRANSIT ADMINISTRATION 58
Calculate the L
dn
at 50 ft from train horns using Eq. 4-9 :
-13.8
Moderate impact (58 dBA)
According to Figure 4-6, the distance correction is approximately -17 dB at 715 ft.
Severe Impact (64 dBA)
According to Figure 4-6, the distance correction is approximately -11 dB at 265 ft.
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Determine the distance from the project noise sources to the impact contours using the fixed-guideway
curve in Figure 4-6 (or the equations in Table 4-15) and the project impact thresholds obtained above. The
project noise at 50 ft is approximately 81 dBA. However, there are at least two intervening rows of
buildings, which will provide 6 dB (4.5 dB for the first row and 1.5 dB for the second row) of shielding.
Project Level
L
dn
Onset of Moderate
Impact
Distance
Onset of Severe
Impact
Distance
81 dBA
715 ft
265 ft
Draw Noise Impact Contours
Contours can be drawn as in Part 1 for ¼ mile on either side of the grade crossing.
Example 4-2 General Noise Assessment – Highway/Transit
General Noise Assessment Example of Highway/Transit Corridor Projects
This example illustrates a highway/transit project where the highway noise dominates and the FHWA
assessment methods should be used to inform the FTA process according to the impact criteria in Section 4.1.
Case 1: Highway Dominates
A new LRT system is planned for the median of a major highway that carries heavy traffic both day and night.
The noise levels at the first row of houses along the highway were measured during peak hour, mid-day and
nighttime with hourly L
eq(1hr)
readings of 65 dBA, 63 dBA, and 60 dBA, respectively. The LRT tracks will be 125
ft from the first row of houses. The LRT operations during peak hour will be 4-car trains at 45 mph, with 5-
minute headways in both directions. Nighttime service decreases to 2-car trains and 20 minute headways.
FTA is providing a share of the funding for the LRT project, but the State DOT and the FHWA are co-lead
agencies because the median requires considerable preparation for the tracks, including replacing bridge piers of
street crossings and moving some highway lanes.
Assumptions
= 82 dBA
d
= 4 cars per train
= 2 cars per train
= 45 mph
= 24 trains per hour
= 6 trains per hour
Estimate Project Noise Exposure at 50 ft
Use Table 4-9 and Table 4-10 to determine the peak hour L
eq(1hr)
for the rail vehicles.
Use Eq. 4-3 to calculate the LRT peak-hour noise level.
dBA at 50 ft
FEDERAL TRANSIT ADMINISTRATION 59
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Use Eq. 4-3 to calculate the LRT late evening hourly noise level.
dBA at 50 ft
Estimate Project Noise Exposure at 125 ft
Since the LRT tracks will be 125 ft from the first row of houses, use Figure 4-6 to determine the level at
125 ft.
At 125 ft, the distance correction is 5 dB.
Peak hour:
Night hourly:
In this case, the highway dominates the noise environment in the area both day and night, by 5 dB during
peak hour and 9 dB at night. According to Section 4.1 and Table 4-2, use the FHWA assessment methods.
Example 4-3 General Noise Assessment – BRT System
General Noise Assessment for a BRT System in an Existing Railroad Right-of-Way
This example for a simple BRT project illustrates using the FTA procedures for a new BRT corridor planned in
an existing abandoned railroad ROW.
Assumptions
= 82 for buses
= 25 mph
= (344 buses) / (15 hours) = 22.9 buses per hour
= (116 buses) / (9 hours) = 12.9 buses per hour
Estimate Project Noise Exposure
Use the information and equations in Table 4-12 to calculate the daytime and nighttime L
eq(1hr)
at 50 ft.
= 15 for buses
dBA at 50 ft
dBA at 50 ft
Calculate L
dn
at 50 ft for the project using Eq. 4-13.
dBA at 50 ft
FEDERAL TRANSIT ADMINISTRATION 60
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Estimate Existing Noise Exposure
The surrounding area is residential with 2,500 people per square mile starting approximately 100 ft away
from the proposed alignment. Determine the existing noise using Table 4-17.
L
dn
= 50 dBA
Determine Noise Level and dIstance for the Onset of Impact
Determine the noise level for the onset of moderate and severe impact using Figure 4-2 and the existing
noise level of 50 dBA. Note that this project is land use category 2 and the appropriate metric is L
dn
.
Existing
Noise
L
dn
Onset of Moderate Impact
L
dn
Onset of Severe
Impact
L
dn
50 dBA
54 dBA
59 dBA
Determine the distance to the noise impact contours using the fixed-guideway & highway curve in Figure
4-6 (or the equations in Table 4-15) and the project impact thresholds obtained above. The project noise
level at 50 ft is approximately 60 dBA.
Moderate impact (54 dBA)
According to Figure 4-6, the distance correction is approximately -6 dB at 125 ft.
Severe Impact (59 dBA)
According to Figure 4-6, the distance correction is less than -1 dB at approximately 60 ft.
Project Level
L
dn
Onset of Moderate
Impact
Distance
Onset of Severe Impact
Distance
60 dBA
125 ft
60 ft
Inventory of Noise Impact
Since there are residential land uses approximately 100 ft away from the proposed alignment and the onset
of moderate impact is at 125 ft, there are possible moderate impacts to the residences.
Noise Mitigation
A barrier is proposed for mitigation between the BRT system and the residences. The analysis is repeated
and results in a predicted new project level of 55 dBA and the following impact distances:
Mitigated Project
Level
L
dn
Onset of Moderate
Impact
Distance
Onset of Severe Impact
Distance
55 dBA
60 ft
N/A
With a noise barrier in place between the BRT system and the residences, it is predicted that the onset of
moderate impact would occur approximately 60 ft away from the BRT system. Since the residential area
begins approximately 100 ft away from the BRT system, which is beyond the distance of moderate impact
(60 ft), a noise barrier would provide the appropriate noise mitigation for the predicted moderate impact.
The onset of severe impact is listed as N/A because with a noise barrier, the severe impact criterion is not
exceeded by the project.
FEDERAL TRANSIT ADMINISTRATION 61
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Example 4-4 General Noise Assessment – Transit Center
General Noise Assessment for a Transit Center
The following example illustrates the procedure for performing a General Noise Assessment for a stationary
source. The example represents a typical FTA-assisted project in an urban area, the siting of a busy transit
center in a mixed commercial and residential area, as shown in Figure 4-8.
Assume that the Noise Screening Procedure has already been done for this project and the nearest residence
has been identified approximately 140 ft from the center of the proposed transit center. Recall that if any
residential or other noise-sensitive land use is identified within 150 ft of a transit center during the Noise
Screening Procedure, additional analysis is required.
Assumptions
Main Street Traffic
Peak hour traffic of 1200 autos, 20 heavy trucks, 300 medium trucks.
Population Density
12 houses per block, single family homes, 3 people per family.
o Block area 78,750 square ft.
o Population density = 9,750 people/square mile.
Bus Traffic
Period
Hours
Buses per
Hour
Peak, Morning
7 a.m.–9 a.m.
30
Peak, Afternoon
4 p.m.–6 p.m.
30
Mid-day
9 a.m.–4 p.m.
15
Evening
6 p.m.–10 p.m.
12
Early Morning (Night)
6 a.m.–7 a.m.
15
Late Night
10 p.m.–1 a.m.
4
Estimate Project Noise Exposure at 50 ft
Determine the hourly volume of buses during day and night.
Daytime (7 a.m. – 10 p.m.)
Nighttime (10 p.m. – 7 a.m.)
Calculate the daytime and nighttime L
eq(1hr)
at 50 ft for the bus transit center using the reference levels in
Table 4-13 and the equations in Table 4-14.
at 50 ft
FEDERAL TRANSIT ADMINISTRATION 62
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
A at 50 ft
Calculate L
dn
at 50 ft for the project using Eq. 4-17.
-13.8
at 50 ft
Estimate Existing Noise Exposure
Estimate existing noise at noise-sensitive sites from the dominant noise source, and either major roadways
or local streets (population density).
Roadway Noise Estimate – The traffic on Main Street qualifies this street for the Other Roadway
category in Table 4-17. According to the map, the nearest residence is 275 ft from the edge of Main
Street. The table shows existing L
dn
= 55 dBA at this distance for representative busy city street traffic.
Population Density Noise Estimate – Noise from local streets is estimated from the population
density of 9,750 people/square mile. Table 4-17 confirms that the L
dn
is approximately 55 dBA.
In this example, the existing noise level by both the roadway and population density estimates are the same,
but that is not always the case. If the levels are different, use the lower noise level. The existing noise level
associated with the residential neighborhood in this example is L
dn
= 55 dBA.
Determine Noise Level and Distance for the Onset of Impact
Determine the noise level for the onset of moderate and severe impact using Figure 4-2 and the existing
noise level of 55 dBA. Note that this project is land use category 2 and the appropriate metric is L
dn
.
Existing Noise
L
dn
Onset of Moderate
Impact
L
dn
Onset of Severe
Impact
L
dn
55 dBA
56 dBA
62 dBA
Determine the distances from the center of the property to the noise impact contours using the stationary
curve in Figure 4-6. The project noise level at 50 ft is 66 dBA.
Moderate impact (56 dBA)
According to Figure 4-6, the distance correction is approximately -10 dB at 125 ft.
Severe impact (62 dBA)
According to Figure 4-6, the distance correction is -4 dB at approximately 70 ft.
Project Noise
L
dn
Onset of Moderate
Impact
Distance
Onset of Severe
Impact
Distance
66 dBA
125 ft
70 ft
Draw Noise Impact Contours
Draw lines at 70 ft and 125 ft from the center of the property of the proposed transit center. These lines
represent the noise impact contours. (Note that in Figure 4-8 the severe impact contour is not drawn for
clarity. The contour is just within the dashed line representing the moderate impact contour after
mitigation).
FEDERAL TRANSIT ADMINISTRATION 63
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Inventory of Noise Impact
Within, or touching, the contour defining moderate impact are three residential buildings (shaded in Figure
4-8). No residences are within the severe impact contour.
Noise Mitigation
The process is repeated with a hypothetical noise barrier at the property line on the residential side of the
transit center. This would consist of a wall approximately 15 ft high partially enclosing the transit center,
sufficient to screen the residences but not the commercial block facing Main Street. According to Table
4-14, the approximate noise barrier effect is -5 dB. Repeating the procedure above, the noise barrier will
reduce the moderate impact contour to 80 ft and the severe impact contour to 45 ft (note that at 50 ft the
distance correction is 0), which in this example eliminates all potential impacts on the residences.
Figure 4-8 Example of Project for General Noise Assessment:
Siting of Transit Center in Mixed Commercial/Residential Area
4.5 Evaluate Impact: Detailed Noise Analysis
Evaluate for impact using the Detailed Noise Analysis procedure in
this section, if appropriate. For guidelines on when the Detailed Noise
Analysis is appropriate, review Section 4.2.
The steps in the Detailed Noise Analysis (Figure 4-9) parallel the steps in the
General Noise Assessment, though the Detailed Noise Analysis employs
equations for computations rather than graphs or tables. Each step in the
Detailed Noise Analysis is more refined in the prediction of project noise and
subsequent evaluation of mitigation measures. Noise projections from the
project must be determined for each receiver.
Step 1: Identify Noise-Sensitive Receivers
Identify the noise-sensitive receivers of interest in the impact analysis study,
including clustering noise-sensitive areas. This identification is usually based
FEDERAL TRANSIT ADMINISTRATION 64
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
on the Screening Procedure and General Noise Assessment previously
conducted.
Step 2: Determine Project Noise Source Reference Levels
Determine the project noise sources and reference levels. Then, estimate
the project noise exposure at the reference distance of 50 ft, considering
operational characteristics. When appropriate, measurements may be used
to determine noise source reference levels.
Step 3: Determine Propagation Characteristics
Estimate project noise exposure as a function of distance, accounting for
shielding and propagation along the path.
Step 4: Combine Noise Exposure from All Sources
Combine all sources to predict the total project noise at receivers.
Step 5: Determine Existing Noise Exposure
Determine the existing noise exposure. Measurements are used to
determine the existing noise exposure. When measurements are
unavailable, a simplified procedure to estimate existing noise exposure may
be used with a clear justification to and approval by the FTA Regional office.
Step 6: Assess Noise Impact
Assess the noise impact at each receiver of interest using separate
procedures for transit only and multimodal transportation projects.
Step 7: Determine Noise Mitigation Measures
Evaluate the need for mitigation and repeat the Detailed Noise Analysis with
proposed mitigation.
When situations arise that are not explicitly covered in the Detailed Noise
Analysis, professional judgment, in consultation with the FTA Regional office,
may be used to extend these methods to cover these unique cases, when
appropriate. Appendix G provides information on developing and using non-
standard modeling procedures.
FEDERAL TRANSIT ADMINISTRATION 65
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Figure 4-9 Procedure for Detailed Noise Analysis
Step 1: Identify Noise-Sensitive Receivers
Select the noise-sensitive receivers of interest, the number of which will depend upon
the land use in the vicinity of the proposed project and the extent of the study area
defined by the Noise Screening Procedure in Section 4.3 and the results of the General
Noise Assessment in Section 4.4.
The steps in identifying the noise-sensitive receivers of interest, both the
number of receivers needed and their locations, shown in Figure 4-10, include:
1a. Identify all noise-sensitive land uses.
1b. Select individual receivers of interest.
1c. Cluster residential neighborhoods and other large noise-sensitive areas.
FEDERAL TRANSIT ADMINISTRATION 66
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Figure 4-10 Guide to Selecting Noise-Sensitive Receivers of Interest
1a. Identify all noise-sensitive land uses where impact is identified by the
General Noise Assessment in Section 4.4. If a General Noise Assessment has
not been done, include all noise-sensitive sites according to the Noise Screening
Procedure in Section 4.3. In areas where ambient noise is low, include land uses
that are farther from the proposed project than for areas with higher ambient
levels.
Recommended materials and methods that can assist in locating noise-sensitive
land uses near the proposed project include:
Land use maps prepared by regional or local planning agencies or by the
project staff. Area-wide maps often do not have sufficient detail to be of
much use. But they can provide broad guidance and may suggest residential
pockets hidden within otherwise commercial zones. Of more use are
project-specific maps that provide building-by-building detail on the land
near the proposed project.
Road and town maps can supplement other maps, are generally more up-
to-date, and may be of larger scale.
Aerial photographs, when current, especially those of 400-ft scale or
better, are valuable in locating all potential noise-sensitive land uses close to
the proposed project. In addition, they can be useful in determining the
distances between receivers and the project.
Windshield survey, in which the corridor is driven and land uses are
annotated on base maps, may be used for definitive identification of noise-
sensitive sites. The windshield survey, supplemented by footwork where
needed, is especially useful in identifying newly-constructed sites and in
confirming land uses very close to the proposed project. In addition, maps
and aerial photos typically reveal only horizontal distances, not vertical
distances. Houses on a hill overlooking the project may need a barrier of
unacceptable height for its attenuation to be effective, and the greater
vertical distance between source and receiver may eliminate the impact
entirely. The windshield survey would reveal where vertical contour maps
FEDERAL TRANSIT ADMINISTRATION 67
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
or other means may be needed so that vertical distances can be
determined.
Geographic Information Systems (GIS) provides electronic ma
pping
needed
for identifying noise-sensitive land uses. GIS data may include la
nd
pa
rcels, building structures, aerial photography, and project-specifi
c
infor
mation. These data may be obtained during the project study
or from
loca
l or regional agencies that store and maintain GIS data. Using electr
onic
GIS d
ata has advantages over paper mapping with respect to automating t
he
pr
ocess of identifying noise-sensitive land uses and accurately being able t
o
determine their distances to the project alignment
Table 4-18 contains three types of land uses of interest and provides guidelines as
to when receivers should be analyzed individually and when they can be
clustered.
Table 4-18 Land Uses of Interest
Land Uses
Specific Use
Selecting Receivers
Residences
Isolated single family residences
Neighborhoods (single and
multi-family residences,
apartment buildings, duplexes,
etc.)
Select each isolated residence as a receiver of interest.
For residential areas, cluster by proximity to project
sources, proximity to ambient-noise sources, and location
along project line. Choose one receiver of interest
(closest to the project noise source and at an
intermediate distance from the predominant sources of
existing noise) in each cluster (i.e., Balance the distance
between the receiver and the new noise source and the
receiver and the existing noise source). Multiple clusters
in one location may be needed to fully characterize the
area.
Indoor noise-
Places of worship
Select noise-sensitive buildings as separate receivers of
sensitive sites
Schools Hospitals/nursing
homes Libraries
Public meeting halls
Concert
halls/auditoriums/theaters
Recording/broadcast studios
Museums and certain historic
buildings
Hotels and motels
Other public buildings with
noise- sensitive indoor use
interest.
Outdoor noise-
Certain parks
For relatively small noise-sensitive areas, select noise-
sensitive areas
Historic sites used for
interpretation
Amphitheaters
Passive recreation areas
Cemeteries
Other outdoor noise-sensitive
areas
sensitive sites as separate receivers of interest.
For relatively large areas (e.g. a cemetery, etc.), cluster by
proximity to project noise sources, proximity to ambient-
noise sources, and location along project line. Choose one
receiver of interest (closest to the project noise source
and at an intermediate distance from the predominant
sources of existing noise) in each cluster.
FEDERAL TRANSIT ADMINISTRATION 68
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
1b. Select the following types of noise-sensitive receivers within the noise study
area, per Table 4-18, to be evaluated as individual receivers:
Every major noise-sensitive public building
Every isolated residence
Every relatively small outdoor noise-sensitive area
Use judgment to avoid analyzing noise where such analysis is obviously not
needed. Areas that are considered particularly noise-sensitive by the
community, but do not meet the criteria in Table 4-3, should be considered on
a case-by-case basis as discussed in Section 4.1.
1c. Residential neighborhoods and relatively large outdoor noise-sensitive areas
can often be clustered, simplifying the analysis that is required without
compromising the accuracy of the analysis. Subdivide all such
neighborhoods/areas into clusters of approximately uniform noise, each
containing a collection of noise-sensitive sites. Strive to obtain uniformity of
both project noise and ambient noise using the following guidelines:
In general, project noise reduces (drops off) with distance from the project.
For this reason, project noise uniformity requires nearly equal distances
between the project noise source and all sites within the cluster. Clusters
are typically shaped as long narrow strips parallel to the transit corridor
and/or circling project point sources such as maintenance facilities. It is
suggested to cluster sites where the project noise varies over a range of 5
dB or less.
Note that noise drops off approximately 3 dB per doubling of distance for
line sources and approximately 6 dB per doubling of distance for point
sources over open terrain. This reduction in noise will occur over a shorter
distance in areas containing obstacles blocking the path of sound
propagation, such as rows of buildings.
Ambient noise usually drops off from non-project sources in the same
manner as noise from project sources. For this reason, clustering for
uniform ambient noise will usually result in long narrow strips parallel to
major roadways or circling major point sources of ambient noise, such as
manufacturing facilities. It is suggested to cluster sites where the ambient
noise varies over a range of 5 dB or less. Ambient noise levels may be
difficult to judge without measurements. In areas without predominant
sources of noise, like highways, ambient noise can be considered to vary
with population density, which is often uniform along the corridor. In
situations where ambient noise tends to be uniform, the clusters can
encompass relatively large areas.
After defining clusters, select one representative receiver in each cluster. It is
recommended to choose the receiver closest to the project noise source and at
an intermediate distance from the predominant sources of existing noise. See
Appendix D for additional guidance and examples on clustering receivers, as
well as an example.
FEDERAL TRANSIT ADMINISTRATION 69
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Assess each identified cluster representative and individual noise-sensitive
receiver of interest using the Detailed Noise Analysis as presented in the
following steps.
Step 2: Determine Project Noise Source Reference Levels
Identify the major project noise sources near the noise-sensitive receivers of interest,
group them by source type, and determine reference levels to compute project noise at
50 ft, as shown in Figure 4-11.
Figure 4-11 Flow Diagram for Determining Project Noise at 50 ft
2a. Identify the major project noise sources near receivers of interest according
to Table 4-19. The right-hand column of the table indicates if each source is
considered as a major contributor to the overall noise impact. Note that some
noise sources can create high noise levels but are not indicated as major
contributors. Although such sources are loud, they rarely stay in a
neighborhood for more than a day or two; therefore, the overall noise
exposure is relatively minor. Computations are required for all major noise
sources in this table.
FEDERAL TRANSIT ADMINISTRATION 70
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Table 4-19 Sources of Transit Noise
Project Type
Source Type
Actual Source
Major?
Commuter Rail
Light Rail Streetcars
RRT
Fixed-Guideway
Locomotive and rail car passbys
Horns and whistles
Crossing signals
Crossovers/switches
Squeal on tight curves
Track-maintenance equipment
Yes
Yes
Yes
Yes
Yes
No
Stationary
Substations
Chiller plants
Yes
No
Busways
Bus Transit Malls
Highway/Transit
Bus passbys
Buses parking
Yes
No
Stationary
Buses idling
Yes
AGT
Monorail
Fixed-Guideway
Vehicle passbys
Yes
Miscellaneous
Line equipment
No
Terminals
Stations
Transit Centers
Fixed-Guideway
Locomotive and rail car passbys
Crossovers/switches
Squeal on tight curves
Yes
Yes
Yes
Highway/Transit
Bus passbys
Buses parking
Automobile passbys
Yes
No
No
Stationary
Locomotives idling
Buses idling
Ferry boats landing, idling, and departing at dock
HVAC equipment
Cooling towers
P/A systems
Yes
Yes
Yes
No
No
No
Park-and-Ride Lots
Highway/Transit
Bus passbys
Buses idling
Automobile passbys
Yes
Yes
No
Stationary
P/A systems
No
Traffic Diversion Projects
Highway/Transit
Highway vehicle passbys
Yes
Storage Facilities
Maintenance Facilities
Fixed-Guideway
Locomotive and rail car passbys
Locomotives idling
Squeal on tight curves
Horns, warning signals, coupling/ uncoupling,
auxiliary equipment, crossovers/ switches, brake
squeal, and air release
Yes
Yes
Yes
Yes
Highway/Transit
Bus passbys
Yes
Stationary
Buses idling
Yard/shop activities
Car washes
HVAC Equipment
P/A Systems
Yes
No
No
No
No
FEDERAL TRANSIT ADMINISTRATION 71
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
2b. Separate the major noise sources by source type: fixed-guideway transit,
highway/transit or stationary facility. Note that a major fixed-guideway system
will usually have stationary facilities associated with it, and that a stationary
facility may have highway/transit elements associated with it. Then use the
instructions in the following source type options below to:
2c. Determine the source reference levels for the all project noise sources.
Each source reference level pertains to reference operating conditions for
stationary sources or one vehicle passby under reference operating conditions.
These reference levels should incorporate source-noise mitigation only if such
mitigation will be considered for incorporation into the system specifications.
The source levels used in this manual are typical of systems designed according
to current engineering practice, but they do not include special noise control
features that could be incorporated in the specifications at extra cost. If special
features that result in noise reductions are included in any of the predictions,
the Federal environmental documents must include a commitment by the
project sponsor to adopt such treatments before the project is approved for
construction. For example, if the specifications include vehicle noise limits that
may not be exceeded, these limits should be used to determine the reference
level, and this level should be used in the analysis rather than the standard,
tabulated reference level.
2d. Convert the source reference level to noise exposure in terms of L
eq(1hr)
or
L
dn
under project operating conditions using the appropriate equations
depending upon the type of source. The noise exposure is determined at the
reference distance of 50 ft.
Option A. Fixed-guideway Sources – Compute project noise at 50 ft for
fixed-guideway sources as identified in the second column of Table 4-19.
A.i. Reference SEL Levels
Determine the reference SEL at 50 ft for each major fixed-guideway noise
source, either by measurement according to Appendix F or by referencing Table
4-20. The table provides guidance on which method is preferred for each
source type. The "NO" designation implies that the source levels given in the
table are appropriate to use in the analysis, and the "YES" designation implies
that measurements are preferred over the data given in the table. In general,
measurements are preferred for source types that vary considerably from
project to project, including any emerging technology sources. The data in the
table are adequate for source types that do not vary considerably from project
to project.
For sources where measurements are preferred, refer to Appendix F for
guidance on measurement procedures and methods for conversion of these
measurements to the reference conditions of Table 4-20. For projects where
source-noise specifications have been defined (e.g., noise limits are usually
included in the specifications for purchase of new transit vehicles), these
specifications may be used instead of measurements after conversion to
reference conditions using the equations in Appendix F. This is only appropriate
when there is a firm commitment to adopt the noise specifications in the vehicle
FEDERAL TRANSIT ADMINISTRATION 72
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
procurement documents during the engineering phase and to adhere to the
specifications throughout the procurement, delivery, and testing of the vehicles.
Approximate
L
max
values are provided in the table for general user information.
As discussed in Appendix B.1.4.2,
L
max
is not used directly in the evaluation of
noise impact.
Table 4-20 Source Reference SELs at 50 ft: Fixed-Guideway Sources at 50 mph
Source
Reference
SEL, dBA
Approximate
L
max
, dBA
Prefer
Measurements? *
Rail cars
82
80
No
Streetcars**
76
74
No
Locomotives – diesel
92
88
No
Locomotives – electric
90
86
No
Diesel multiple unit (DMU)
85
81
Yes
Agt – steel wheel
80
78
Yes
Agt – rubber tire
78
75
Yes
Monorail
82
80
Yes
Maglev
72
70
Yes
Transit car horns (emergency)
93
90
No
Transit car whistles
81
78
No
Locomotive horns
At-grade crossing
113
110
No
From crossing to 1/8 mile
†
110
From 1/8 mile to 1/4 mile
110
110
* "No" implies that the source levels given in the table are appropriate to use in the analysis and
"Yes" implies that measurements are preferred over the data given in the table.
** The reference speed for streetcars is 25 mph. For streetcar speeds above 25 mph, use the “Rail
Cars” reference level and 50 mph for the reference speed.
† Use the following equation for locomotive horns from crossing to 1/8 mile:
)
where:
= distance from grade crossing parallel to tracks
A.ii. Estimate Noise Exposure at 50 ft – Use the reference SELs in Table
4-20, operating conditions, and the equations in Table 4-21 to predict the noise
exposure at 50 ft expressed in terms of L
eq(1hr)
and L
dn
. Follow the steps below:
1. Identify operating conditions – Trains with different numbers of cars or
operating conditions produce different noise exposure levels and should be
converted from SEL to L
dn
separately. Use the following guidelines to
determine if sources should be converted separately. These differences in
operating conditions will produce an approximate 2-decibel change in noise
exposure:
40 percent change in number of locomotives or cars per train.
40 percent change in number of trains per hour.
40 percent change in number of trains per day, or per night (for
computation of L
dn
).
15 percent change in train speed.
Change of one notch in diesel locomotive throttle setting (e.g., from
notch 5 to notch 6).
FEDERAL TRANSIT ADMINISTRATION 73
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
2. Establish relevant time periods – For each of these source types and
conditions, determine the relevant time periods for all receivers that may be
a
ffected by this sourc
e.
For r
esidential receivers, the time periods of interest fo
r
c
omputation of L
dn
are: daytime (7 a.m. to 10 p.m.) and nighttime
(
10 p.m. to 7 a.m.)
.
If
the source will affect non-residential receivers, the time period o
f
inter
est is the loudest hour of project-related activity during
hours
of
noise sensitivity. Several different hours may be of interest f
or
non
-residential receivers depending on the hours the facility is us
ed.
3. Co
llect input d
ata
Sour
ce reference SELs for locomotives, rail cars, and warning horns
.
Number of rail cars in the train (if this number varies during the
day
, take the average for the daytime and nighttime per
iods
s
eparately for category 2 land uses, and use the maximum n
umber
during the period of interest for category 1 or 3 land uses).
N
umber of locomotives in the train, if any
.
Train speed, in miles per hour (maximum expected).
A
verage throttle setting of the train's locomotive(s) for diesel-
powered locomotives and DMU’s only.(
iv
)
If this input is not
a
vailable, assume a throttle setting of 8 for locations where t
he
vehicle would accelerate and 5 for all other locations.
(
25
)
For residential receivers of interest:
A
verage hourly train volume during daytime hours (the tota
l
number of train passbys between 7 a.m. and 10 p.m., divided by
15
hours)
;
A
verage hourly train volume during nighttime hours (the tota
l
number
of train passbys between 10 p.m. and 7 a.m., divided
by
9
hours)
;
For non
-residential receivers of interest, number of events tha
t
occ
ur during each hour of interest in trains per hour; a
nd
T
rack type (continuously welded or jointed) and profile (at-grade
or
elevated).
4. Calculate L
eq(1hr)
at 50 ft
Ca
lculate L
eq(1hr)
using the appropriate equations in Table 4-21 for
ea
ch hour of interest
.
Compute the combined L
eq(1hr)
. It may be necessary to compute the
c
ombined totals with and without the warning horns; som
e
neig
hborhoods along the corridor may be exposed to the
horn
nois
e and some may not
.
5. Cal
culate L
dn
at 50 ft
If
the project noise will affect any residential receivers, calculate t
he
L
dn
using the combined day L
eq(1hr)
and the combined night L
eq(1hr)
.
It
may be necessary to calculate L
dn
with and without the warning
horns
, as a
bove.
iv
Omit this term if not applicable from the equation in Table 4-21 for other vehicle types.
FEDERAL TRANSIT ADMINISTRATION 74
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Note that the equations in Table 4-21 include terms to account for a difference
in speed from the reference speed of 50 mph and a numerical adjustment to
account for the one-hour time period for this metric. For more information on
the numerical adjustment to represent the time period of interest, see
Appendix B.1.4.4.
FEDERAL TRANSIT ADMINISTRATION 75
L
eq(1hr)
at 50 ft
Eq. 4-25
Locomotive
Warning
Horns
**
L
eq(1hr)
at 50 ft
Eq. 4-26
Rail Vehicles
†
L
eq(1hr)
at 50 ft
Eq. 4-27
Streetcar
(25 mph or slower)
L
eq(1hr)
at 50 ft
Eq. 4-28
Transit
Warning
Horns
**
L
eq(1hr)
at 50 ft
Eq. 4-29
Combined
Locomotive and
transit
††
L
eq(1hr)
at 50 ft
Eq. 4-30
Daytime
L
d
at 50 ft
where V = V
d
, N
Loco
= N
d
(loco events), and N
Cars
= N
d
(car events)
Eq. 4-31
Nighttime
L
n
at 50 ft
where V = V
n
, and N
Loco
= N
d
(loco events), and N
Cars
= N
d
(car
Eq. 4-32
events)
Day/Night
L
dn
at 50 ft
Eq. 4-33
=
average number of locomotives per train
=
where
T = average throttle setting for diesel-powered locomotives and DMUs only
= -10 for passenger diesel
Ŧ
0 for DMUs
+10 for electric
= average number of cars per train
= average hourly volume of train traffic, trains per hour
S
= train speed, mph
= constant
+5 for jointed track or for a crossover within 300 ft
+4 for aerial structure with slab track (except AGT and monorail)
+3 for embedded track on grade
V
d
= average hourly daytime volume of train traffic, V
n
= average hourly nighttime volume of train traffic,
trains per hour trains per hour
N
d
= average hourly number of events that occur N
n
= average hourly number of events that occur during
during daytime (7 a.m. to 10 p.m.) nighttime (10 p.m. to 7 a.m.)
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Table 4-21 Computation of L
eq(1hr)
and L
dn
at 50 ft: Fixed-Guideway Sources
Locomotives
*
* Assumes a diesel locomotive power rating at approximately 3000 hp ** Based on FRA’s horn noise model (www.fra.dot.gov/Elib/Document/2681)
† Includes all commuter rail cars, transit cars, streetcars above 25 mph, AGT and monorail. †† Only include appropriate terms.
Ŧ
Because of the wide range of vehicle types that qualify as a DMU, measurements are preferred for the reference level and speed coefficient. If
no measurements are conducted, use the reference level in Table 4-20 and a speed coefficient of 0.
FEDERAL TRANSIT ADMINISTRATION 76
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Example 4-5 Detailed Noise Analysis – Fixed Guideway Noise Sources
Computation of L
eq(1hr)
and L
dn
at 50 ft for Fixed-Guideway Source
A commuter train with 1 diesel locomotive and 6 cars will pass close to a residential area at a grade crossing.
The track is jointed.
Assumptions
= 92 for diesel locomotives
= 82 for rail cars
= 113 for locomotive warning horns at-grade crossing
= 6
= 1
= 43 mph
= 8
=
=
Use the equations in Table 4-21 to determine the daytime L
eq(1hr)
for each source and the combined daytime
L
eq(1hr)
at 50 ft.
at 50 ft
at 50 ft
at 50 ft
With horn:
in neighborhoods where the horn is sounded
Without horn:
in neighborhoods where the horn is not sounded
Use the same equations as above to determine the nighttime L
eq(1hr)
at 50 ft. Use V
n
instead of V
d
.
= 56.5 for locomotives
= 51.3 for cars
= 70.9 for horns
= 71.1 in neighborhoods where the horn is sounded
= 57.6 in neighborhoods where the horn is not sounded
Calculate the L
dn
with and without horns.
FEDERAL TRANSIT ADMINISTRATION 77
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
With horn:
at 50 ft in neighborhoods where horns are sounded
Without horn:
at 50 ft in neighborhoods where horns are not sounded
Note: Computation results should always be rounded to the nearest decibel at the end of the computation. In
all examples of this section, however, the first decimal place is retained for readers to precisely match their own
computations against the example computations.
Option B. Highway/Transit Sources – Compute project noise at 50 ft for
highway/transit noise sources as identified in the second column of Table 4-19.
Use the instructions below to estimate source noise levels for projects
following FTA’s procedures that involve highway vehicles.
This method is based on the original FHWA highway noise prediction model,
with updated noise emission levels.
(
26
)
The vehicle equations are applicable to
speeds typical of freely-flowing traffic on city streets and access roads.
B.i. Reference SEL Levels – Determine the reference SEL at 50 ft for each
maj
or highway/transit source, either by measurement according to Appendix
F
or by
using Table 4-22.
(
v
)
The table provides guidance on which method is
pr
eferred for each source type. “NO" implies that the source levels given in t
he
table are appropriate to use in the analysis, and "YES" implies that
mea
surements are preferred over the data given in the table. For sources wher
e
measurements are preferred, refer to Appendix F for guidance on measurement
pr
ocedures and methods for conversion of measurement data to the referenc
e
c
onditions in Table 4-
20.
A
pproximate
L
max
values are provided in the table for general user information.
As discussed in Appendix B.1.4.2,
L
max
is not used directly in the evaluation of
noise impact.
Table 4-22 Source Reference SELs at 50 ft: Highway/Transit Sources at 50 mph
Source
Reference
SEL, dBA
Approximate
L
max
, dBA
Prefer
Measurements?*
Automobiles
74
70
No
Buses (diesel)
82
79
No
Buses (electric trolleybus)
80
77
No
Buses (hybrid)**
83
80
Yes
* "No" implies that the source levels given in the table are appropriate to use in the analysis and
"Yes" implies that measurements are preferred over the data given in the table.
** Hybrid bus with full-time diesel engine and electric drive motors.
v
Idling buses are considered stationary sources.
FEDERAL TRANSIT ADMINISTRATION 78
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
B.ii. Noise Exposure at 50 ft – Use the reference SELs in Table 4-22,
operating conditions, and the equations in Table 4-23 to predict the noise
exposur
e at 50 ft expressed in terms of L
eq(1hr)
and L
dn
. Follow the steps below:
1. Identify operating conditions – Noise emission from most transit buses
is
not dependent upon whether the buses are accelerating or cruising
.
Howev
er, accelerating suburban buses are substantially louder than cruis
ing
s
uburban buses. For this reason, suburban buses require separat
e
c
alculation along roadway stretches where they are accelerating. Separat
e
c
alculation is also needed for all highway/transit vehicles at different speeds
,
s
ince speed affects noise emissions. Use the following guidelines t
o
det
ermine if sources should be calculated separately. These differences
in
oper
ating conditions will produce an approximate 2-decibel change in nois
e
exposure:
40
percent change in number of vehicles per hour
;
40
percent change in number of vehicles per day, or per night (
for
computation of L
dn
); or
15
percent change in vehicle s
peed.
2. E
stablish relevant time periods – For each of these source types a
nd
c
onditions, determine the relevant time periods for all receivers that may
be
a
ffected by this sourc
e.
For r
esidential receivers, the time periods of interest
for
c
omputation of L
dn
are: daytime (7 a.m. to 10 p.m.) and nighttime
(
10 p.m. to 7 a.m.)
.
If the source will affect non-residential receivers, the time period of
inte
rest is the loudest hour of project related activity during
hours
of
noise sensitivity. Several different hours may be of interest f
or
non
-residential receivers depending on the hours the facility is us
ed.
3. Co
llect input d
ata
Sour
ce reference SELs for the vehicle types of concer
n
A
verage running speed in miles per h
our
For residential receivers of interest:
A
verage hourly vehicle volume during daytime hours (tota
l
number of vehicle passbys between 7 a.m. and 10 p.m., divided
by
15)
.
A
verage hourly vehicle volume during nighttime hours (tota
l
number
of vehicle passbys between 10 p.m. and 7 a.m., div
ided
by
9)
.
For
non-residential receivers of interest, number of events tha
t
occ
ur during each hour of interest, in vehicles per hou
r
4. Cal
culate L
eq(1hr)
at 50 ft – Calculate L
eq(1hr)
using the appropriate
equa
tions in Table 4-23 for each hour of interest
.
5. Cal
culate L
dn
at 50 ft – If the project noise will affect any residential
r
eceivers, calculate the L
dn
using the day L
eq(1hr)
and night L
eq(1hr)
.
No
te that the equations in Table 4-23 include terms to account for a difference
in speed from the reference speed of 50 mph and a numerical adjustment to
FEDERAL TRANSIT ADMINISTRATION 79
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
account for the one-hour time period for this metric. For more information on
the numerical adjustment to represent the time period of interest, see
Appendix B.1.4.4.
Table 4-23 Computation of L
eq(1hr)
and L
dn
at 50 ft: Highway/Transit Sources
L
eq(1hr)
at 50
ft
Eq. 4-34
Daytime
L
d
at 50 ft
where V = V
d
Eq. 4-35
Nighttime
L
n
at 50 ft
where V = V
n
Eq. 4-36
L
dn
at 50 ft
Eq. 4-37
Adjustments
= -3 for automobiles, open-graded asphalt
= +3 for automobiles, grooved pavement
S
V
d
V
n
= average hourly volume of vehicles, vehicles per hour
= for buses
for hybrid buses
(23)
for accelerating 3-axle commuter buses
for automobiles
= average vehicle speed, mph (distance divided by time, excluding stop
time at red lights)
= average hourly daytime volume of vehicles of this type, vehicles per hour
= average hourly nighttime volume of vehicles, vehicles per hour
Example 4-6 Detailed Noise Analysis – Highway Transit Noise Sources
Computation of L
eq(1hr)
and L
dn
at 50 ft for Highway/Transit Source
A bus route with city buses will pass close to a school that is in session from 8 a.m. to 4 p.m. on weekdays.
Within this time period, the hour of greatest activity for this bus route is 8 a.m. to 9 a.m.
Assumptions
= 82 dBA
= 40 mph
= 30 buses per hour
Use the equations in Table 4-23 to determine the hourly L
eq(1hr)
at 50 ft.
at 50 ft
FEDERAL TRANSIT ADMINISTRATION 80
=
=
Calculate the daytime and nighttime L
eq(1hr)
at 50 ft.
at 50 ft
at 50 ft
Calculate L
dn
at 50 ft.
at 50 ft
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
This same bus also passes close to a residential area with the following operating conditions:
Note: Computation results should always be rounded to the nearest decibel at the end of the computation. In
all examples of this section, however, the first decimal place is retained for readers to precisely match their own
computations against the example computations.
Option C. Stationary Sources – Compute project noise at 50 ft for
stationary sources as identified in the second column of Table 4-19.
C.i. Determine Reference SEL Levels – Determine the reference SEL at 50
ft for each major stationary source, either by measurement according to
Appendix F or by using Table 4-24. The table provides guidance on which
method is preferred for each source type. "NO" implies that the source levels
given in the table are appropriate to use in the analysis, and "YES" implies that
measurements are preferred over the data given in the table. In general,
measurements are preferred for source types that vary considerably from
project to project. For example, curve squeal is highly variable depending on
weather conditions, curve radius, and train speed. The data in the table are
adequate for source types that do not vary considerably from project to project
(crossing signals, for example). For sources where measurements are preferred,
refer to Appendix F for guidance on measurement procedures and methods for
conversion of these measurements to the reference conditions of Table 4-24.
Layover facilities and transit centers can be the sources of low-frequency noise
from idling diesel engines. Sounds with considerable low-frequency components
can cause greater annoyance than would be expected based on their A-
weighted levels. Low-frequency sounds often cause windows and walls to
vibrate resulting in secondary effects in buildings such as rattling of dishes in
cupboards and wall-mounted pictures. The reference levels in Table 4-24 are
adjusted to take increased annoyance into account. For a Detailed Noise
Analysis at locations where such idling takes place for an extended period, use
the method described in ANSI Standard S12.9-Part 4, Annex D.
(
27
)
Approximate L
max
values are provided in the table for general user information.
As discussed in Appendix B.1.4.2,
L
max
is not used directly in the evaluation of
noise impact.
FEDERAL TRANSIT ADMINISTRATION 81
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Table 4-24 Source Reference SELs at 50 ft: Stationary Sources
Source
Reference
SEL, dBA
Approximate
L
max
, dBA
Prefer
Measurements?*
Auxiliary Equipment
101
65
Yes
Locomotive Idling
109
73
No
Rail Transit Idling
106
70
No
Buses Idling
111
75
No
Ferry Boat Landing**, Idling, and Departing
91
78
No
Ferry Boat Fog Horn
90
84
No
Track Curve Squeal
136
100
Yes
Car Washes
111
75
Yes
Crossing Signals
109
73
No
Substations
99
63
No
* "No" implies that the source levels given in the table are appropriate to use in the analysis, and "YES" implies
that measurements are preferred over the data given in the table.
**Ferry boat landings are included in the stationary source category because the noise from the landing remains
in one area even though the boats move in and out.
C.ii. Estimate Noise Exposure at 50 ft – Use the reference SELs in Table
4-
24, operating conditions, and the equations in Table 4-25 to predict the nois
e
exposure at 50 ft expressed in terms of L
eq(1hr)
and L
dn
. Follow the steps below:
1. I
dentify operating conditions – Identify actual source durations an
d
number
s of events. Sources with different operating conditions should
be
c
onverted from SEL to L
dn
separately. Use the following guidelines to
det
ermine if sources should be converted separately. These differences
in
operating conditions will produce an approximate 2-dB change in noise
exposure:
40
percent change in event duration (e.g., from 30 to 42 minutes)
,
or
40
percent change in number of events per hour (e.g., from 10 t
o
14
events per hour)
.
2. E
stablish relevant time periods – For each of these source types a
nd
conditions, determine the relevant time periods for all receivers that may be
a
ffected by this sourc
e.
For residential receivers, the time periods of interest for
c
omputation of L
dn
are: daytime (7 a.m. to 10 p.m.) and nighttime
(
10 p.m. to 7 a.m.)
.
If
the source will affect non-residential receivers, the time period o
f
inter
est is the loudest hour of project related activity during
hours
of
noise sensitivity. Several different hours may be of interest f
or
non
-residential receivers depending on the hours the facility is us
ed.
3.
Co
llect input d
ata
Sour
ce reference SELs for each relevant sourc
e
A
verage duration of one event, in second
s
For r
esidential receivers of interest
:
A
verage number of events per hour that occur during t
he
day
time (the total number of events between 7 a.m. and
10
p.
m., divided by 15)
.
FEDERAL TRANSIT ADMINISTRATION 82
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Average number of events per hour that occur during the
nighttime (the total number of events between 10 p.m. and 7
a
.m., divided by 9)
.
For non
-residential receivers of interest, number of events tha
t
occ
ur during each hour of interest in events per h
our
4. Cal
culate L
eq(1hr)
at 50 ft – Calculate L
eq(1hr)
using the appropriate
equa
tions in Table 4-25 for each hour of interest
.
5. Cal
culate L
dn
at 50 ft – If the project noise will affect any residential
r
eceivers, calculate the L
dn
using the day L
eq(1hr)
and night L
eq(1hr)
.
Note that the equations in Table 4-25 include a numerical adjustment to
account for the one-hour time period for this metric. For more information on
the numerical adjustment to represent the time period of interest, see
Appendix B.1.4.4.
Table 4-25 Computation of L
eq(1hr)
and L
dn
at 50 ft: Stationary Sources
L
eq(1hr)
at 50
ft
Eq. 4-38
Daytime
L
d
at 50 ft
where N = N
d
Eq. 4-39
Nighttime
L
n
at 50 ft
where N = N
n
Eq. 4-40
L
dn
at 50 ft
Eq. 4-41
E*
N
d
N
n
= number of events of this type that occur during one-hour
= duration of one event, sec
= average hourly number of events that occur during daytime
(7 a.m. to 10 p.m.)
= average hourly number of events that occur during nighttime
(10 p.m. to 7 a.m.)
*Omit the term containing E for ferry boat, and fog horn noise sources.
FEDERAL TRANSIT ADMINISTRATION 83
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Example 4-7 Detailed Noise Analysis – Stationary Noise Sources
Computation of L
eq(1hr)
and L
dn
at 50 ft for Stationary Sources
A signal crossing lies close to a school that is in session from 8 a.m. to 4 p.m. on weekdays. Within this time
period, the hour of greatest activity for the signal crossing is 8 a.m. to 9 a.m.
Assumptions
= 109 dBA
= 25 seconds (counting both cycles of the signal)
= 22
Use the equations in Table 4-25 to determine the hourly L
eq(1hr)
at 50 ft.
at 50 ft
This same signal crossing lies close to a residential area with the following operating conditions:
=
=
Calculate the daytime and nighttime L
eq(1hr)
at 50 ft.
at 50 ft
at 50 ft
Calculate L
dn
at 50 ft.
at 50 ft
Note: Computation results should always be rounded to the nearest decibel at the end of the computation. In
all examples of this section, however, the first decimal place is retained for readers to precisely match their own
computations against the example computations.
Step 3: Determine Propagation Characteristics
Determine the combined propagation characteristics between each source and receiver
of interest.
3a. Calculate project noise exposure as a function of distance. Calculate the
project noise exposure at distances other than 50 ft, such as at receiver locations, as a
function of distance accounting for shielding and ground effects along the path. See
Example 4-8 below.
FEDERAL TRANSIT ADMINISTRATION 84
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
1. Determine the topography of the ground within the transit corridor using
the figures in Table 4-26 as a guide. It is not necessary to represent the
transit corridor with an extreme number of changes in topography. Often,
several typical sections will suffice throughout the transit corridor.
2. Use the equations in Table 4-26 to determine ground factor (G) based on
the effective path height (Heff) for each identified terrain feature. Standard
source heights are included at the bottom of the table. Assume receiver
heights of 5 ft for both outdoor receivers and first-floor receivers. Note
that larger ground factors correspond to larger amounts of ground
attenuation with increasing distance from the source. For acoustically "hard"
(e.g., non-absorptive) ground conditions, G should be taken to be zero.
3. Determine the distance correction factor using the ground factor and
another distance, such as the distance to a receiver, and the equations in
Table 4-27.
4. Apply the distance correction (C
distance
) to the project noise exposure at 50
ft (Section 4.5, Step 2) using the following equation:
Eq. 4-42
where:
=
or
at the new distance, ft
=
or
at 50 ft
5. Plot noise exposure as a function of distance if desired.
FEDERAL TRANSIT ADMINISTRATION 85
Table 4-26 Ground Factor G, for Ground Attenuation
Ground Factor
Soft Ground:
Eq. 4-43
H
eff
= sum of average path heights on either side of the barrier, see below.
Hard Ground:
Eq. 4-44
Figure 4-12 Flat Ground
Use Eq. 4-44
Figure 4-13 Source in Shallow Cut
Figure 4-14 Elevated Receiver
Use Eq. 4-44
Figure 4-15 Source in Sloped Cut
Figure 4-16 Source and Receiver Separated by Trench
= 8 ft for trains with diesel-electric locomotives = 3 ft for 2-axle city buses
= 2 ft for trains without diesel-electric locomotives
= 8 ft for 3-axle commuter buses
= 0 ft for automobiles
Note: Equations for H
eff
remain valid when H
b
= 0
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
FEDERAL TRANSIT ADMINISTRATION 86
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Table 4-27 Distance Correction Factor Equations for Detailed Noise Analysis
Source
Equation*
Stationary Sources
Eq. 4-45
Fixed-guideway rail car passbys
Eq. 4-46
Fixed-guideway locomotive and rubber-
tired vehicle passbys, highway vehicle
passbys and horns
Eq. 4-47
distance, ft
ground factor, see Table 4-26
*These equations assume the distance between the source and receiver is approximately 300 ft or less. At longer
distances, ground effects have an upper limit and atmospheric conditions may affect propagation characteristics. Therefore,
more detailed calculation methods may be required to account for those effects.
Example 4-8: Detailed Noise Analysis – Exposure vs. Distance Curve
Exposure vs. Distance Curve for Fixed-Guideway Source
Plot an exposure vs. distance curve for a diesel-electric commuter train that does not sound the horn in this
area.
Assumptions
The terrain is flat grassland without a noise barrier.
= 72 dBA at 50 ft
= 68 dBA at 50 ft
H
r
= 5 ft
H
b
= 0 ft (for a “no noise barrier” case)
H
s
= 8 ft (for a diesel-electric commuter train)
Calculate H
eff
using the equations in Table 4-26.
= 6.5 ft
Determine the ground factor using Eq. 4-43.
Use Eq. 4-45 to determine noise vs. exposure equations for L
d.loco
and L
dn.loco
.
=
=
Plot the two equations (see example in Figure 4-17). From these curves, the noise levels due to this train
operation can be determined for a receiver of interest at any distance without shielding.
FEDERAL TRANSIT ADMINISTRATION 87
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Figure 4-17 Example Exposure vs. Distance Curves
3b. Calculate the attenuation due to shielding for each distance of interest from
Step 3a, using the following equation and Tables 4-26 through 4-30 and as
illustrated in Example 4-9. If the conditions described in the tables are not met,
the attenuation due to shielding is considered zero. Shielding can be due to
intervening noise barriers, terrain features, rows of buildings, and dense tree
zones.
Eq. 4-48
where:
= barrier insertion loss, see Table 4-28
= attenuation due to buildings, see Table 4-29
= attenuation due to trees, see Table 4-30
Table 4-28 Barrier Insertion Loss
Barrier
Insertion
Loss
Eq. 4-49
P
G
NB
G
B
For non-absorptive transit barriers within 5 ft of the rail
)}
For absorptive transit barriers within 5 ft of the rail
For all other barriers, and for protrusion of terrain
above the line of sight
= path length difference, ft (see figure 4-18)*
= closest distance between the receiver and the source, ft
= ground factor G computed without barrier (see Table 4-26)
= ground factor G computed with barrier (see Table 4-26)
* If the source height (exhaust outlet) for diesel-electric locomotives is not available, assume 15 ft.
FEDERAL TRANSIT ADMINISTRATION 88
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Figure 4-18 Noise Barrier Parameter "P"
Table 4-29 Attenuation due to Buildings
Condition
Equation
Gaps in the row of buildings constitute less
than 35% of the length of the row
Eq. 4-50
Gaps in the row of buildings constitute 35 to
65% of the length of the row
Eq. 4-51
Gaps in the row of buildings constitute more
than 65% of the length of the row
= number of rows of houses that intervene between the source and receiver
Table 4-30 Attenuation due to Trees
Condition
Equation
At least 100 ft of trees intervene between the
source and receiver with no clear line-of-sight
between source and receiver, and the trees
extend 15 ft or more above the line-of-sight
Eq. 4-52
W = width of tree zone along the line-of-site between the source and receiver in feet
Example 4-9: Detailed Noise Analysis – Shielding
Computation of Shielding
The following features are between the rail corridor and a receiver of interest. Calculate the attenuation due to
shielding.
1. A 15-foot high noise barrier is 40 ft from the closest track and 130 ft from the receiver
2. A dense tree zone 100 ft thick that extends 15 ft above the line-of-sight
Assumptions
H
s
= 8 ft
H
r
= 5 ft
Barrier dimensions
A
= 40.61 ft
B
= 130.38 ft
C
= 170.03 ft
Barrier
Calculate H
eff
with and without the barrier using the equations in Table 4-26.
FEDERAL TRANSIT ADMINISTRATION 89
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
= 6.5 ft
= 21.5 ft
Determine the ground factor with and without the barrier using Eq. 4-43.
Calculate the barrier insertion loss using Table 4-28 and Figure 4-18.
ft
= 12.8 dB
=
= 12.8 dB
= 11.4 dB
Trees
Determine the attenuation due to trees using Table 4-30.
dB
Total Shielding
The total shielding is the maximum of the barrier and tree zone shielding, 11.4 dB.
= 11.4 dB
Note: Computation results should always be rounded to the nearest decibel at the end of the computation. In
all examples of this section, however, the first decimal place is retained for readers to precisely match their own
computations against the example computations.
FEDERAL TRANSIT ADMINISTRATION 90
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
3c. Combine the two propagation characteristics.
Combine the results from Steps 3a and 3b to determine the noise at the
receiver considering the propagation characteristics of distance and shielding by
applying the distance correction and attenuation due to shielding to the project
noise exposure level at 50 ft.
The equations in Table 4-31 combine the equations in Steps 3a and 3b.
Table 4-31 Calculate L
dn
or L
eq(1hr)
Source
Equation*
Stationary Sources
Eq. 4-53
Fixed-guideway rail car
passbys
Eq. 4-54
Fixed-guideway locomotive
and rubber-tired vehicle
passbys, highway vehicle
passbys and horns
Eq. 4-55
distance, ft
= ground factor, see Section 4.5, Step 3a
= attenuation due to shielding, see Section 4.5, Step 3b.
*These equations assume the distance between the source and receiver is approximately 300 ft or less. At longer
distances, ground effects have an upper limit and atmospheric conditions may affect propagation characteristics.
Therefore, more detailed calculation methods may be required to account for those effects.
(
28
,
29
)
Step 4: Combine Noise Exposure from All Sources
Combine all sources to predict the total project noise at the receivers using the
equations in Table 4-32 after propagation adjustments have been made for the noise
exposure from each source separately.
Table 4-32 Computing Total Noise Exposure
Total L
eq(1hr)
from all sources
for the hour of interest:
)
Eq. 4-56
Total L
dn
from all sources
)
Eq. 4-57
Example 4-10 Detailed Noise Analysis – Combine Sources
Computation of Total Exposure from Combined Sources
Combine the noise exposure from the commuter train and light rail system to estimate the total noise exposure
at the receiver.
Assumptions
A commuter train operation produces the following levels at a receiver of interest:
= 72 dBA
= 68 dBA
A light rail system produces the following levels at the same receiver:
= 69 dBA
FEDERAL TRANSIT ADMINISTRATION 91
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
= 70 dBA
No other project sources affect this receiver.
Calculate the total noise exposure at the receiver using the equations in Table 4-32.
dBA
dBA
Note: Computation results should always be rounded to the nearest decibel at the end of the computation. In
all examples of this section, however, the first decimal place is retained for readers to precisely match their own
computations against the example computations.
Step 5: Determine Existing Noise Exposure
Choose the appropriate method for characterizing noise and then determine the
existing noise at each identified noise-sensitive receiver. The existing noise is needed
to determine the noise impact according to the criteria described in Section 4.1,
Step 2. Recall that impact is assessed based on a comparison of the existing
ambient noise exposure and the additional noise exposure that will be caused by
the project. The existing noise exposure must be estimated for all receivers of
interest identified in Section 4.5, Step 1.
For a Detailed Noise Analysis, it is recommended to measure existing noise at
each receiver of interest identified in Section 4.5, Step 1
, for the most precise
assessment of existing noise and conclusions concerning noise impact. However,
measurements are expensive, often thwarted by weather, and take considerable
time in the field. If taking measurements at each identified receiver is not
possible, other less precise methods are available. Different methods may be
used at different receivers along the project. However, it is important to
recognize the correlation between the precision of measurements and the
confidence in the impact assessment. Especially in a Detailed Noise Analysis,
avoid using less precise methods of measuring existing noise just for the sake of
convenience or expediency. The use of less precise methods must be clearly
justified.
Option A. Noise Exposure Measurements – Full one-hour measurements
are the most appropriate way to determine ambient noise exposure for
non-residential receivers with the level of precision expected in a Detailed
Noise Analysis. For residential receivers, full 24-hour measurements are more
appropriate. These full-duration measurements are preferred over other
methods of characterizing existing noise where time and study funds allow.
Follow the procedures below for these full-duration ambient noise exposure
measurements:
Ai. Non-residential land uses – Measure a full hour L
eq(1hr)
at the receiver of
interest on at least two non-successive weekdays (generally between noon on
Monday and noon on Friday). Select the hour of the day when the maximum
project activity is expected to occur.
FEDERAL TRANSIT ADMINISTRATION 92
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
A.ii. Residential land uses – Measure a full 24-hour L
dn
at the receiver of
inter
est for a single weekday (generally between noon on Monday and noo
n on
Fr
iday)
.
A.i
ii. Microphone position – The location of the microphone at the receiv
er
depends u
pon the proposed location of the transit noise source, so use go
od
t
echnical judgment in positioning the measurement microphone. If, for exa
mple,
a
new rail line will be in front of the house, do not locate the microphone in t
he
ba
ckyard behind the house where the line of sight between the noise sourc
e
and receiver is obstructed. Figure 4-19 illustrates recommended measurement
posi
tions for various locations of the project, with respect to the house and t
he
existing source of ambient noise.
A.iv. Measurement guidelines – Undertake all measurements in accordance
with good engineering practice following guidelines given in ASTM and ANSI
s
tandards.
(
30
)(
31
)
Figure 4-19 Recommended Microphone Locations
for Existing Noise Measurements
FEDERAL TRANSIT ADMINISTRATION 93
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Option B. Noise Exposure Computations from Partial Measurements
– Often, measurements can be made at some of the receivers of interest and
used to estimate noise exposure at nearby receivers. In other situations, several
L
eq(1hr)
measurements can be taken at a receiver and then the L
dn
computed
from these. Both options require experience and knowledge of acoustics to
select representative measurement sites. If using this method to compute an
Ldn, a minimum time period of one hour should be used for each measurement
period. It is unacceptable to extrapolate a one hour measurement from a
shorter measurement period.
Measurements at one receiver can be used to represent the noise environment
at other sites, but only when proximity to major noise sources is similar among
the sites. Residential neighborhoods with otherwise similar homes may have
greatly varying noise environments. For example, one area of the neighborhood
may be located where the ambient noise is clearly due to highway traffic. A
second area toward the interior of the neighborhood may have highway noise as
a factor, but also include other noise sources from the community. A third area
located deep into the residential area could have local street traffic and other
community activities dominate the ambient noise. In this example, three or
more measurement sites would be required to represent the varying ambient
noise conditions in a single neighborhood.
Typical situations where representative measurement sites can be used to
estimate noise levels at other sites occur when both share the following
characteristics:
Proximity to the same major transportation noise sources, such as
highways, rail lines and aircraft flight patterns
Proximity to the same major stationary noise sources, such as power
plants, industrial facilities, rail yards and airports
Similar type and density of housing, such as single-family homes on
quarter-acre lots and multi-family housing in apartment complexes
Acoustical professionals are often adept at such computations from partial data
and are encouraged to use their experience and judgment in fully utilizing the
measurements in their computations. This does necessitate a conservative
estimate (underestimate) of existing noise to account for reduced precision
from partial data as compared to full noise measurements.
Those without a background in acoustics are encouraged to use the procedures
in Appendix E to compute existing noise from partial measurements. These
methods include a factor to conservatively estimate (underestimate) existing
noise to account for reduced precision from partial data as compared to full
noise measurements.
Option C. Estimating Existing Noise Exposure – The least precise way to
determine noise exposure is to estimate it from a table. This method is often
used for the General Noise Assessment, but it is not recommended for a
Detailed Noise Analysis. It can be used, however, in the absence of better data
for locations where roadways or railroads are the predominant ambient noise
source. Table 4-17 presents these existing levels. The levels in Table 4-17 are
FEDERAL TRANSIT ADMINISTRATION 94
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
conservative and underestimate existing noise to account for reduced precision
compared to full noise measurements. If a simplified procedure to estimate
existing noise exposure is chosen it must be clearly justified and receive
approval by the FTA Regional office.
While measurements are considered the most precise method, there is one
situation where it may be more accurate to estimate rather than measure the
existing noise exposure, which is in areas near major airports where aircraft
noise is dominant. Because airport noise is highly variable based on weather
conditions and corresponding runway usage, it is preferable in such cases to
base the existing noise exposure on published aircraft noise contours in terms
of Annual Average L
dn
.
Step 6: Assess Noise Impact
Assess noise impact at each receiver of interest identified in Section 4.5, Step 1
using the noise impact criteria in Section 4.1 and the procedures in this step.
Choose the appropriate noise impact assessment procedure for a transit
project or multimodal project.
Option A. Transit Projects – For transit projects, noise impact is assessed at
each receiver of interest using the criteria for transit projects described in
Section 4.1. The noise impact assessment procedure is as follows:
A.i. Tabulate existing ambient noise exposure (rounded to the nearest whole
decibel) at all receivers identified Section 4.5, Step 1. In cases where large
residential buildings are exposed to noise on one side only, the receivers on
that side are included in the analysis.
A.ii. Tabulate project noise exposure at these receivers from Section 4.5,
Step 4.
A.iii. Determine the level of noise impact (no impact, moderate impact, or
severe impact) according to Section 4.1.
A.iv. Document the results in noise-assessment inventory tables. Include the
following information:
Receiver identification and location
Land use description
Number of noise-sensitive sites represented (number of dwelling units
in residences or acres of outdoor noise-sensitive land)
Closest distance to the project
Existing noise exposure
Project noise exposure
Level of noise impact (no impact, moderate impact, or severe impact)
A sum of the total number of receivers and numbers of dwelling units
predicted to experience moderate impact or severe impact
A.v. Illustrate the areas of moderate impact and severe impact. Two methods
of displaying impact are labeling and contouring.
FEDERAL TRANSIT ADMINISTRATION 95
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
In a Detailed Noise Analysis, the most accurate indication of impact is
to label each impacted building or cluster identified in the inventory
table.
A less precise illustration of impacted areas is a plot of project noise
contours on the maps or aerial photographs, along with shaded impact
areas. Use the procedures in Section 4.4, Step 6 and the levels from
Section 4.5, Step 2 to develop these contours.
Note that it is difficult to position noise contours in urban areas due to
shielding, terrain features, and other propagation anomalies. If noise contours
are used, they should be considered illustrative rather than definitive. If desired
to conform to the practices of another agency, the contouring may perhaps
include several contour lines of constant project noise, such as L
dn
65, L
dn
70,
and L
dn
75 dBA.
A.vi. Including information on the magnitude of the impacts is an essential part
of the assessment. The magnitude of noise impact is defined by the two
threshold curves delineating onset of moderate impact and severe impact.
Option B. Multimodal Projects – For multimodal projects, project noise
comprised of both highway and transit noise sources that are assessed
according to the FTA noise impact criteria (see Table 4-2), use the procedure in
Option A above. For multimodal projects that require FHWA’s noise
assessment methods to inform FTA’s evaluation (see Section 4.1, Step 1 -
Option B), follow the FHWA guidance.
(
32
)
In general, the appropriate calculation
method is to use the current version of FHWA’s Traffic Noise Model (TNM).
(22)
TNM is a state-of-the-art computer program used for predicting noise impacts
near highways.
TNM allows for a detailed assessment at each receiver of interest by separately
calculating the noise contribution of each roadway segment. For each roadway
segment, the noise from each vehicle type is computed from reference noise
levels, adjusted for:
Vehicle volume
Vehicle speed
Grade
Roadway segment length
Source-to-receiver distance
Further adjustments needed to accurately model the sound propagation from
source to receiver include:
Shielding provided by rows of buildings,
Effects of different ground types,
Source and receiver elevations, and
Effect of any intervening noise barriers.
TNM sums the noise contributions of each vehicle type for a given roadway
segment at the receiver. TNM then repeats this process for all roadway
segments, summing their contributions to generate the predicted noise level at
each receiver.
FEDERAL TRANSIT ADMINISTRATION 96
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Step 7: Determine Noise Mitigation Measures
Evaluate alternative mitigation measures where the Detailed Noise Analysis
shows either severe or moderate impact, and it is not feasible to change the
alignment or location of the project to avoid impact. Project noise that is found
to cause no impact does not generally require any mitigation.
Mitigation of noise impact from transit projects may involve treatments at the
three fundamental components of the noise problem: at the noise source, along
the source-to-receiver propagation path, or at the receiver. Generally, the
transit property has authority to treat the source and some elements of the
propagation path, but may have little or no authority to modify anything at the
receiver. After mitigation options have been determined, repeat the project
noise computations including the adopted mitigation and reassess the remaining
noise impact.
Approximate costs for noise control measures are documented in a report
from the Transit Cooperative Research Program (TCRP)
(
33
)
and are also
presented in this section. These costs reflect the noise mitigation costs available
in 1997 (unless otherwise noted), which are the most recent data available as of
this publication, and should only be used as representative estimates when
considering noise mitigation options. Current noise mitigation costs should be
researched before decisions on noise mitigation options are finalized, and then
they should be documented according to Section 8.
7a. Evaluate Source Treatments – The most effective noise mitigation
treatments are applied at the noise source. This is the preferred approach to
mitigation when possible. Common source treatments and their estimated
acoustical effectiveness are included in Table 4-33 and described below. It is
important to note that the values below are estimates and should be applied
with good engineering judgement. It also important to note that these mitigation
measures should not be applied as a reduction in the reference SEL values for a
vehicle that already incorporates that measure as a feature, such as vehicle
skirts. Measurements to determine the reference SEL source level are required
in those instances.
Table 4-33 Transit Noise Mitigation Measures – Source Treatments
Mitigation Measure
Effectiveness
Stringent Vehicle & Equipment Noise Specifications
Varied
Operational Restrictions†
Varied
Resilient or Damped Wheels*
For rolling noise on tangent track:
2 dB
For wheel squeal on curved track:
10-20 dB
Vehicle Skirts*
6-10 dB
Undercar Absorption*
5 dB
Quiet Fan Design and Fan Placement*
Varied
Preventative Maintenance on Rail Systems*
Varied
Resurfacing Roads**
10 dB
Guideway Support for Buses**
10 dB
Turn Radii Greater than 1000 ft*
Avoids Squeal
Rail Lubrication on Sharp Curves*
Reduces Squeal
Movable-Point Frogs (reduce rail gaps at crossovers)*
Reduces Impact Noise
Engine Compartment Treatments
6-10 dB
Quiet Zones*
Reduces occurrence of horn noise
†FTA does not normally accept operational restrictions as a noise mitigation measure – see below.
* Applies to rail projects only.
** Applies to bus projects only.
FEDERAL TRANSIT ADMINISTRATION 97
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Stringent Vehicle and Equipment Noise Specifications
Vehicles – Among the most effective noise mitigation treatments is
nois
e control during the specification and design of the transit vehic
le.
Suc
h source treatments apply to all transit modes. By developing an
d
en
forcing stringent but achievable noise specifications, the trans
it
pr
operty takes a major step in controlling noise everywhere on t
he
s
ystem. It is important to ensure that the noise levels quoted in t
he
s
pecifications are achievable with the application of best availa
ble
t
echnology during the development of the vehicle and reas
onable
c
onsidering the noise reduction benefits and c
osts.
Effec
tive enforcement includes penalties for non-compliance with the
specifications. The noise mitigation achieved by source treatment is
dependent on the quality of installation and maintenance. Vehicles failing
to meet the noise specification could result in complaints from the
public and require additional noise mitigation measures applied along the
path or at receivers.
Stationary sources – Stringent but achievable noise specifications
for
s
tationary sources are also an effective approach for mitigating nois
e
impa
cts. Typical equipment includes fixed plant equipment such a
s
t
ransformers and mechanical equipment, as well as grade-cross
ing
s
ignals. For example, it may be possible to reduce noise impact fr
om
g
rade-crossing signals in some areas by specifying equipment that set
s
t
he level of the warning signal lower in locations where ambient noise
is
lower
to minimize the signal noise in the direction of noise-sens
itive
receivers.
O
perational Restrictions – Changes in operations that can mitigate nois
e
inc
lude the lowering of speed, the reduction of nighttime (10 p.m. to 7 a.m.
)
oper
ations, and reduction of warning horns and signals
.
S
peed reduction – Because noise from most transit vehicles
is
dependen
t on speed, a reduction of speed results in lower noise levels
.
T
he effect can be considerable. For example, the speed dependency
of
s
teel-wheel/steel-rail systems for L
eq(1hr)
and L
dn
(Table 4-21) results in a
6-
dB reduction when reducing the speed to half of the original s
peed.
A
lthough there are tangible benefits from speed reductions during the
most noise-sensitive time periods, FTA does not ordinarily accept speed
reduction as a noise mitigation measure for two important reasons:
speed reduction is unenforceable and negated if vehicle operators do
not adhere to established policies, and it is contrary to the purpose of
the transit investment by FTA, which is to move as many people as
possible as efficiently and safely as possible.
Reduction of nighttime operations – Complete elimination
of
nig
httime operations has a strong effect on reducing the L
dn
, because
nig
httime noise is increased by 10 dB when calculating L
dn
. But
r
estrictions on operations are usually not feasible because of servic
e
demands
. FTA generally does not pursue restrictions on operations as
a
FEDERAL TRANSIT ADMINISTRATION 98
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
noise reduction measure. However, if early morning idling can be
curtailed to the minimum necessary, however, this can have a
measurable effect on L
dn
.
While there are tangible benefits from limits on operations during the
most noise-sensitive time periods, FTA does not recommend limits on
operations as a way to reduce noise impacts because it is contrary to
the purpose of the transit investment by FTA which is to move as many
people as possible as efficiently and safely as possible.
Reduction of warning horns and signals – Minimizing or eliminat
ing
horns
and other warning signals at gate crossings can reduce nois
e
impa
ct for light rail and commuter rail systems. Although thes
e
mitigation options are limited by safety considerations, they can be
effec
tive in the right circumstances. For examples, see quiet z
ones
below
and wayside horns in Step
7b.
W
heel Treatments (Rail) – A major source of noise from steel-wheel
and steel-rail systems is the wheel/rail interaction that can produce three
distinctive sounds: roar, impact, and squeal (as discussed in Section 3.2).
Roar is the rolling noise caused by small-scale roughness on the wheel tread
and rail running surface. Impacts are caused by discontinuities in the running
surface of the rail or by a flat spot on the wheels. Squeal occurs when a
steel-wheel tread or its flange rubs across the rail, resulting in resonant
vibrations in the wheel that creates a screeching sound. Various wheel
designs and other mitigation measures exist to reduce the noise from each
of these three mechanisms.
Resilient wheels – Resilient wheels are effective in eliminating wheel
s
queal on tight turns with reductions of 10 to 20 dB in the high-
frequency range where squeal noise occurs. Rolling noise is also slight
ly
r
educed with resilient wheels and typically achieves a 2-dB reduction
on
t
angent track. The costs for resilient wheels are approximately $2000 t
o
$3000
per wheel, as compared to about $400 to $700 for standar
d
s
teel wheels.
(
vi
)
Damped wheels – Damped wheels, like resilient wheels, are effective
in
eliminating wheel squeal on tight turns with reductions of 5 to 15
dB
in the high-frequency range where squeal occurs. Rolling noise is also
s
lightly reduced by approximately 2 dB on tangent track. This treatmen
t
inv
olves attaching vibration absorbers to standard steel wheels. T
he
c
osts for damped wheels add approximately $500 to $1000 to t
he
norma
l $700 for each steel whee
l.
vi
Assumes 8 wheels per vehicle.
FEDERAL TRANSIT ADMINISTRATION 99
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Vehicle Treatments – Vehicle noise mitigation measures are applied to
the various mechanical systems associated with propulsion, ventilation, and
pa
ssenger comfort. Propulsion systems of transit vehicles include dies
el
eng
ines, electric motors, and diesel-electric combinations. Noise from t
he
pr
opulsion system depends on the type of unit and how much nois
e
mit
igation is built into the design. Mufflers on diesel engines are generall
y
r
equired to meet noise specifications; however, mufflers are generall
y
pr
actical only on buses, not on locomotives. Control of noise from eng
ine
c
asings may require shielding the engine by body panels without louvers
,
dic
tating other means of cooling, and ventilati
on.
V
entilation requirements for vehicle systems are related to the noise
generated by a vehicle. Fan noise often remains a major noise source after
other mitigation measures have been instituted because of the need to have
direct access to cooling air. This applies to heat exchangers for electric
traction motors, diesel engines, and air-conditioning systems. The mitigation
options for these systems include:
Quiet fan design and placement – Fan noise can be reduced
by
ins
tallation of quiet, efficient fans. Forced-air cooling on electric tract
ion
mo
tors can be quieter than self-cooled motors at operating speeds
.
Pla
cement of fans on the vehicle can make a considerable difference
in
t
he noise radiated to the wayside or to patrons on the statio
n
pla
tforms
.
Veh
icle skirts and undercar absorption – The vehicle body desig
n
can provide shielding and absorption of the noise generated by the
v
ehicle components. Acoustical absorption under the car has
been
demo
nstrated to provide up to 5 dB of mitigation for wheel/rail nois
e
a
nd propulsion-system noise on rapid transit trains. Similarly, vehic
le
s
kirts over the wheels can provide more than 5 dB of mitigation.
By
c
arrying their own noise barriers, vehicles with these features ca
n
pr
ovide cost-effective noise reduction. The cost for vehicle skirts wi
ll
a
dd approximately $5000 to $10000 per vehicle. Undercar abs
orption
wi
ll add approximately $3500 per vehicle, assuming that 50% of th
e
under
side of the floor is treat
ed.
P
reventative Maintenance (Rail) – Preventative maintenance is the bes
t
strategy to minimize rail and wheel deterioration. While these are not
mit
igation measures in the traditional sense and should not be included a
s
mit
igation in an environmental document, they can help to keep both nois
e
a
nd vibration levels at a “like-new” level or reduce both noise and vibrati
on
in
systems with deferred maintenance. This can be accompanied
by
c
onsiderable life cost benefits for the transit syste
m.
S
pin-slide control systems – Similar to anti-locking brake syst
ems
(
ABS) on automobiles, spin-slide control systems reduce the incidenc
e
of
wheel flats, a major contributor of impact noise. Trains with smoot
h
whee
l treads can be up to 20 dB quieter than those with wheel flats. T
o
be
effective, the anti-locking feature should be in operation during a
ll
braking phases, including emergency braking. Wheel flats are more likely
FEDERAL TRANSIT ADMINISTRATION 100
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
to occur during emergency braking than during dynamic braking. The
cost of slip-slide control may be incorporated in the new vehicle costs,
but may be between $5,000 and $10,000 per vehicle with a maintenance
cost of $200 per year.
Wheel truing – Maintenance of wheels by truing eliminates wheel flats
from the treads and restores the wheel profile. As discussed above,
wheel flats are a major source of impact noise. As a guideline, it is
recommended that wheel sets match within approximately ±0.01 inch
and all wheels on the same truck should match within ±0.02 inches to
minimize damage and wear to wheels and rails.
(
34
)
A wheel truing
machine costs approximately $1 million, including associated
maintenance materials and labor costs. The TCRP report estimates a
system with 700 vehicles would incur a yearly cost of $300,000 to
$400,000 for a wheel truing program.
It is recommended to install wheel-flat detector systems to identify
vehicles that are most in need of wheel truing. These systems are
becoming more common on railroads and intercity passenger systems,
but are relatively rare on transit systems.
Rail grinding – The smoothness of the running surface is critical in t
he
mit
igation of noise from a moving vehicle. Mill scale grinding befor
e
c
ommencement of pre-revenue service train operations is critica
l.
Exper
ience shows that grinding new rails after approximately 3 mont
hs
of
train operations and scheduling routine grinding at approximat
e
intervals of 2 years in the problem areas would minimize noise
pr
oblems related to corrugation in most cases. Grinding with smal
l
mac
hines when the corrugation depth is still small is a reas
onable
a
pproach. As a guideline, it is recommended to spot-grind at locati
ons
wher
e corrugation occurs before corrugation grows to 0.02 inches (32)
.
Per
iodic rail grinding can result in a net savings per year on wheel and
rail wear. Most transit systems contract out rail grinding, although some
of the larger systems make the investment of approximately $1 million
for the equipment and do their own grinding. Contractors typically
charge a fixed amount per day for the equipment on site, plus an
amount per pass-mile (one pass of the grinding machine for one mile).
Typical rail grinding cost would be approximately $7,000 to $10,000 per
pass-mile.
Wheel and rail profile matching – It is important to consider t
he
whee
l and rail profile compatibility when truing wheels and gr
inding
r
ails. If the profiles do not match, the benefits of this kind
of
pr
eventative maintenance will not be achiev
ed.
It
is equally important to consider initial wheel and rail profile
compatibility. Work with track designers and vehicle suppliers early in
the design process to ensure wheel and rail profile compatibility.
Profiles should be defined during the design phase and should be in
FEDERAL TRANSIT ADMINISTRATION 101
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
place when system opens.
(32)
The cost of wheel and rail profile matching
may be incorporated in the new vehicle and new rail costs.
Profile grinding of the rail head in combination with a wheel truing
program may be the most practical approach to controlling and
reducing noise and vibration where such practices are not normally
conducted.
Maintenance program – Clearly defined maintenance specificat
ions
s
hould be developed during design phase of the project. T
he
specifications should define rail and wheel profiles, include detailed
g
uidance for pre-revenue mill scale grinding, address issues related t
o
healthy rail-wheel interface, and include a mechanism for periodic
mo
nitoring of wheel and rail condition and verification
for
compliance.
(32)
A diligent maintenance program can often resolve or
reduce rail noise issues before they occur. Vehicle reconditioning
pr
ograms should also be developed particularly for components such a
s
s
uspension system, brakes, wheels, and slip-slide detectors
.
Gu
ideway Support (Bus) – The smoothness of the running surface
is
c
ritical in the mitigation of noise from a moving vehicl
e.
R
esurfacing roads – Roughness on the guideway can be eliminated
by
r
esurfacing roads, thereby reducing noise levels by up to 10 dB
.
Br
idge expansion joint angles and design – Bridge expansion joint
s
a
re also a source of noise for rubber-tire vehicles. This source of nois
e
can be reduced by placing expansion joints on an angle or by specifying
t
he serrated type rather than joints with right-angle edges
.
Turn R
adii and Rail Lubrication – For steel-wheel/steel-rail syst
ems
wi
th non-steerable trucks and sharp turns, squeal can typically be eliminate
d
by
designing all turn radii to be greater than 1000 ft, or 100 times the truc
k
whee
lbase, whichever is less. If this is not possible, squeal can be mitigat
ed
by
installation of lubricators (though the potential environmental impacts
of
lubr
icant application should be factored into this decision).Rail lubricat
ors
c
ost approximately $10,000 - $40,000 per curv
e.
M
ovable-point and Spring-rail Frogs – Frogs with spring-
loaded
mechanisms and frogs with movable points can reduce impact noise near
c
rossovers. According to the TCRP report, a spring frog c
osts
a
pproximately $12,000, twice the cost of a standard frog. A movable p
oint
fr
og involves elaborate signal and control circuitry resulting in higher c
osts
of a
pproximately $200,00
0.
U
se of Locomotive Horns at-grade Crossings and Quiet Zones –
In
c
ases where commuter rail operations share tracks or ROW with freight
or
inter
city passenger trains that are part of the general railroad system, th
e
s
afety rules of the FRA, including the Train Horn Rule, apply.
(
35
)
The Train
Hor
n Rule requires that locomotive horns be sounded at public highwa
y
g
rade crossings, although some exceptions are allowed in carefully
defined
c
ircumstances. Locomotive horns are often a major contribut
or in
FEDERAL TRANSIT ADMINISTRATION 102
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
projections of adverse noise impact, in the community from proposed
commuter rail projects. Since noise barriers are not feasible at highway-rail
grade crossings, the establishment of quiet zones could be considered.
Quiet zones can be established in which supplemental safety measures
(SSMs) are used in place of the locomotive horn to provide an equivalent
level of safety at-grade crossings.
(
vii
)
By adopting an approved SSM at each
public grade crossing, a quiet zone of at least a half-mile long can be
established. These measures are in addition to the standard safety devices
required at most public grade crossings (e.g., stop signs, reflectorized
crossbucks, flashing lights with gates that do not completely block travel
over the tracks). Below are four SSMs that have been predetermined by the
FRA to fully compensate for the lack of a locomotive horn:
Temporary closure of a public highway-rail grade crossing
–
T
his measure requires closure of the grade crossing for one period eac
h
24
hours, and the closure must occur at the same time each day
.
F
our-quadrant gate system – This measure involves the installat
ion
of
at least one gate for each direction of traffic to fully block vehic
les
fr
om entering the crossing
.
Ga
tes with medians or channelization devices – This measur
e
keeps traffic in the proper travel lanes as it approaches the crossing.
T
his denies the driver the option of circumventing the gates by traveli
ng
in the opposing lane.
O
ne-way street with gates – This measure consists of one-wa
y
streets with gates installed, so that all approaching travel lanes are
completely
block
ed.
In
addition to the pre-approved SSMs, the FRA rule also identifies a range of
other measures that may be used in establishing a quiet zone. These could
include modified SSMs or non-engineering types of measures, such as
increased monitoring by law enforcement for grade crossing violations or
instituting public education and awareness programs that emphasize the
risks associated with grade crossings and applicable requirements. These
alternative safety measures (ASMs) require approval by FRA based on a
demonstration that public safety would not be compromised by eliminating
horn usage.
The lead agency for designating a quiet zone is the local public authority
responsible for traffic control and law enforcement on the roads crossing
the tracks. To satisfy the FRA regulatory requirements, the public transit
agency must work closely with this agency while also coordinating with any
freight or passenger railroad operator sharing the ROW. The final
environmental document should discuss the main considerations in adopting
the quiet zone including: the engineering feasibility, receptiveness of the
local public authority, consultation with the railroad, preliminary cost
estimates, and evidence of the planning and interagency coordination that
has occurred to date. If a quiet zone will be relied on as a mitigation
measure, the final environmental document should provide reasonable
vii
For more information on quiet zones, visit: https://www.fra.dot.gov/Page/P0889.
FEDERAL TRANSIT ADMINISTRATION 103
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
assurance that any remaining issues can and will be resolved. For more
information on documentation requirements see Section 8.
The cost of establishing a quiet zone varies considerably, depending on the
number of intersections that must be treated and the specific SSMs, ASMs,
or combination of measures that are used. The FRA gives a cost estimate of
$15,000 per crossing for installing two 100-foot-long, non-traversable
medians that prevent motorists from driving around closed gates. A typical
installation of a four-quadrant gate system is in the range of $175,000–
$300,000 per crossing.
(
36
)
Who pays for the installation of modifications can
become a major consideration in a decision to pursue a quiet zone
designation, especially in cases where noise from preexisting railroad
operations is controversial in the community. In many cases where a quiet
zone would mitigate a severe impact caused by the proposed transit project,
the costs are covered by the project sponsor and FTA in the same
proportion as the overall cost-sharing for the project.
7b. Evaluate Path Treatments – When noise mitigation treatments cannot
be applied at the noise source or additional mitigation is required after treating
the source, the next preferred placement of noise mitigation is along the noise
propagation path between the source and receiver. Common path treatments
and their estimated acoustical effectiveness are included in Table 4-34 and
described below.
Table 4-34 Transit Noise Mitigation Measures – Path Treatments
Mitigation Measure
Effectiveness
Noise barriers close to vehicles
6-15 dB
Noise barriers at row line
3-15 dB
(37)
Alteration of horizontal & vertical alignments
Varied
Wayside horns
Varied
Acquisition of buffer zones
Varied
Ballast on at-grade guideway*
3 dB
Ballast on aerial guideway*
5 dB
Resilient track support on aerial guideway
Varied
Vegetation and trees
Varied, see Table 4-30
* Applies to rail projects only.
Noise Barriers – Noise barriers are effective in mitigating noise when they
break the line-of-sight between source and receiver. The mechanism of
sound shielding is described in Section 3.3. The necessary height of a barrier
depends on the source height and the distance from the source to the
barrier, see Table 4-28 and Figure 4-18.
Noise barriers close to vehicles – Barriers located very close to a
rapid transit train, for example, may only need to be approximately 3 to
4 ft above the top of rail to be effective. Standard barriers close to
vehicles can provide noise reductions of 6 to 10 dB.
Noise barriers at ROW line – Barriers on the ROW line or for
trains on the far track, the height must be increased to provide
equivalent effectiveness to barriers located close to the vehicles.
Otherwise, the effectiveness can drop to 3 dB or less, even if the
barrier breaks the line-of-sight.
FEDERAL TRANSIT ADMINISTRATION 104
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
All barrier effectiveness can be increased by as much as 5 dB by applying
sound-absorbing material to the inner surface of the barrier. The length of
the barrier wall is also important to its effectiveness. The barrier must be
long enough to block noise from a moving train along most of its visible
path. This is necessary so that train noise from beyond the ends of the
barrier will not severely compromise noise-barrier performance at noise-
sensitive locations. The barrier length can be refined in the engineering
phase, closely examining the predicted sound level exceedances at specific
receivers, site geometries, and the contribution of barrier flanking noise,
then adjusting the length as appropriate.
Noise barriers can be made of any outdoor weather-resistant solid material
that meets the minimum sound transmission loss required by the project.
Materials that are commonly used for noise barriers include 16-gauge steel,
1-inch thick plywood, and any reasonable thickness of concrete. Typically, a
surface density of 4 pounds per square foot is required. Areas with strong
winds may require more stringent structural requirements. It is critical to
seal any gaps between barrier panels and between the barrier and the
ground or elevated guideway deck for maximum performance.
Costs for noise barriers (based on highway installations) range from $20 to
$25 per square foot of installed noise barrier at-grade with additional cost
for design and inspection.
(
38
)
Installation on aerial structures could be twice
the amount of installation at-grade, especially if the structure has to be
strengthened to accommodate the added weight and wind load.
As described in Section 3.3, noise barriers, if not designed and sited
carefully, can reduce visibility of trains for pedestrians and motorists, which
causes safety concerns. It is important to consult with safety experts in
choosing and siting a noise barrier.
Alteration of Horizontal and Vertical Alignments – Transit alignment
in a cut as part of grade separation can accomplish the same result as
installation of a noise barrier at-grade or on aerial structure. The walls of
the cut serve the same function as barrier walls in breaking the line-of-sight
between source and receiver.
Wayside Horns – The sounding of a locomotive horn as the train
approaches an at-grade intersection produces a very wide noise footprint in
the community. Using wayside horns at these intersections instead of the
locomotive horn can substantially reduce the noise footprint without
compromising safety at the grade crossing.
A wayside horn does not need to be as loud as a locomotive horn, and the
warning sound is focused only on the area where it is needed. These are
pole-mounted horns used in conjunction with flashing lights and gates at the
intersection, with a separate horn oriented toward each direction of
oncoming vehicle traffic. Noise levels in nearby residential and business
areas can be reduced substantially with wayside horns, depending on the
location with respect to the grade crossing.
FEDERAL TRANSIT ADMINISTRATION 105
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
A plan to use wayside horns in place of the locomotive horn at public grade
crossings must be coordinated with several public and private entities,
notably the local agency having responsibility for traffic control and law
enforcement on the road crossings, the state agency responsible for railroad
safety, any railroads that share the ROW, and FRA. Public notification must
also be given. Preliminary cost information from testing programs indicates a
wayside horn system at a railroad/highway grade crossing costs
approximately $50,000.
Buffer Zones – Because noise levels attenuate with distance, one nois
e
mitigation option is to increase the distance between noise sources and the
c
losest noise-sensitive receivers. This can be accomplished by locat
ing
alignments away from noise-sensitive sites. Acquisition of land or purchasing
ea
sements for noise buffer zones is an option that may be considered
if
appropriate for the project.
Gro
und Absorption – Ballast on Guideways – Propagation of nois
e
over
ground is affected by whether the ground surface is absorptive
or
r
eflective. Noise from vehicles on the surface is strongly affected by t
he
c
haracter of the ground in the immediate vicinity of the vehicle. Roads an
d
s
treets for buses are hard and reflective, but the ground at the side of
a
r
oad has a substantial effect on the propagation of noise to greater distanc
e.
G
uideways for rail systems can be either reflective or absorptive, depe
nding
on
whether they are concrete or ballast. Ballast on a guideway can reduc
e
t
rain noise 3 dB at-grade and up to 5 dB on an aerial structur
e.
Vegetation and Trees – In almost all cases, vegetation and trees are
ineffec
tive at providing noise mitigation. Vegetation and Trees can pr
ovide
s
ome mitigation if at least 100 ft of trees intervene between the source a
nd
r
eceiver, if no clear line-of-sight exists between the source and receiver, a
nd
if
the trees extend 15 ft or more above the line-of-sight as described
in
Sec
tion 4.5, Step 3b. This is generally not a recommended form
of
mit
igation to purs
ue.
7c. Evaluate Receiver Treatments – Consider treatments to the receivers
when noise mitigation treatments cannot be applied at the source or along the
propagation path, or if combinations of treatments are required. Common
receiver treatments and their estimated acoustical effectiveness are included in
Table 4-35 and are described in this section.
Table 4-35 Transit Noise Mitigation Measures – Receiver Treatments
Mitigation Measure
Effectiveness
Acquisition of Property Rights for Construction of Noise Barriers
5-10 dB
Building Noise Insulation
5-20 dB
Noise Barriers – In certain cases, it may be possible to acquire limited
pr
operty rights for the construction of noise barriers at the receiver. A
s
dis
cussed above, barriers need to break the line-of-sight between the nois
e
s
ource and the receiver to be effective and are most effective when they ar
e
FEDERAL TRANSIT ADMINISTRATION 106
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
closest to either the source or the receiver. See Section 3.3 for more
information on noise barriers.
Building Insulation – In cases where noise barriers are not feasible—such
as multi-story buildings, buildings very close to the ROW, or grade
crossings—the only practical noise mitigation measure may be to provide
sound insulation for the buildings. In these cases, the need for mitigation at
locations where impact has been identified will depend on the use (outdoor
vs. indoor), any existing outdoor to indoor reduction in noise levels, and the
feasibility of constructing effective noise barriers for second stories and
above.
Depending on the quality of the original building façade, especially windows
and doors, sound insulation treatments can improve the noise reductions
from transit noise by 5 to 20 dB. To be considered cost-effective, a
treatment should provide a minimum reduction of 5 dB in the interior of
the building and meet the L
dn
45 dBA interior criterion. For more
information, see Section 4.1.
In many cases, especially in locations with high ambient noise levels, the
existing sound insulation of a building may already meet the 45 dBA L
dn
interior noise criterion. It is recommended that sound insulation testing be
conducted to determine if the existing sound insulation is sufficient or what
additional measures would be required to meet the interior criterion.
Effective treatments include:
Caulking and sealing gaps in the building façade; and
Installation of new doors and windows that are specially designed to
meet acoustical transmission-loss requirements:
- Exterior doors facing the noise source should be replaced with
well-gasketed, solid-core wood doors and well-gasketed storm
doors.
- Acoustical windows are typically made of multiple layers of glass
with air spaces between to provide noise reduction. Acoustical
performance ratings are published in terms of Sound Transmission
Class (STC) for these windows. It is recommended to use a
minimum STC rating of 39 on any window exposed to the noise
source.
These treatments are beneficial for heat insulation as well as for sound
insulation, but acoustical windows are typically non-operable and central
ventilation or air conditioning is needed. Residents’ preferences should be
considered.
If needed, additional building sound insulation can be provided by sealing
vents and ventilation openings and relocating them to a side of the building
away from the noise source. In cases where the noise sources is low-
frequency noise from diesel locomotives, it may be necessary to increase
the mass of the building façade for wood-frame houses by adding a layer of
sheathing to the exterior walls.
FEDERAL TRANSIT ADMINISTRATION 107
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Examples of residential sound insulation for rail or highway projects are
limited. However, much practical experience with sound insulation of
buildings has been gained through grants for noise mitigation to local airport
authorities by FAA.
FEDERAL TRANSIT ADMINISTRATION 108
SECTION
5
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Transit Vibration
This section presents the basic concepts of transit ground-borne vibration, also
referred throughout this manual as simple “vibration,” and low-frequency
groundborne-noise that sometimes results from vibration. The steps for the
screening and assessing of potential vibration impacts of transit projects for FTA
NEPA approval are described in the following sections.
The Source-Path-Receiver framework for ground-borne vibration for a rail
system illustrated in Figure 5-1 is central to all environmental vibration studies.
The train wheels rolling on the rails create vibration energy that is transmitted
through the track support system into the transit structure. The vibration of the
transit structure excites the adjacent ground, creating vibration waves that
propagate through the ground and into nearby buildings creating ground-borne
vibration effects that potentially interfere with activities. The vibrating building
components may radiate sound, which this manual refers to as ground-borne
noise. Airborne noise from transit sources is covered in Sections 2.3–4.5 of this
manual. Ground-borne noise refers to the noise generated by ground-borne
vibration.
Figure 5-1 Propagation of Ground-Borne Vibration into Buildings
This section contains the following:
Section 5.1 The ground-borne vibration and noise metrics used in this
manual
Section 5.2 An overview of transit vibration sources
FEDERAL TRANSIT ADMINISTRATION 109
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Section 5.3 An overview of transit vibration paths
Sec
tion 5.4 An overview of receiver factors of transit vibration and
a
dis
cussion of the technical background for ground-borne noise criter
ia
5.1 Ground-Borne Vibration and Noise Metrics
Vibration is an oscillatory motion that can be described in terms of the
displacement, velocity, or acceleration. Because the motion is oscillatory, there
is no net movement of the vibration element and the average of any of the
motion metrics is zero. Displacement is the most intuitive metric. For a
vibrating floor, the displacement is simply the distance that a point on the floor
moves away from its static position. The velocity represents the instantaneous
speed of the floor movement and acceleration is the rate of change of the
speed.
Although displacement is easier to understand than velocity or acceleration, it is
rarely used for describing ground-borne vibration. Most transducers used for
measuring ground-borne vibration use either velocity or acceleration.
Furthermore, the response of humans, buildings, and equipment to vibration is
more accurately described using velocity or acceleration.
This manual uses the metrics outlined in Table 5-1 for transit ground-borne
vibration and noise measurements, computations, and assessment. These
metrics are consistent with common usage in the United States.
Table 5-1 Ground-borne Vibration and Noise Metrics
Metric
Abbreviation
Definition
Vibration Decibels
VdB
The vibration velocity level in decibel scale.
Peak Particle Velocity
PPV
The peak signal value of an oscillating vibration velocity waveform.
Usually expressed in inches/second in the United States.
Root Mean Square
rms
The square root of the arithmetic average of the squared amplitude of
the signal.
A-weighted Sound Level
dBA
A-weighted sound levels represent the overall noise at a receiver that
is adjusted in frequency to approximate typical human hearing
sensitivity. This unit is used to characterize ground-borne noise.
The metrics in the table above are illustrated in Figure 5-2. The components in
the figure include:
Raw signal – This curve shows the instantaneous vibration velocity
,
which fluctuates positively and negatively about the zero point.
P
eak particle velocity (PPV) – PPV is the maximum instantan
eous
positive or negative peak of the vibration signal. PPV is often used in
mo
nitoring of construction vibration (such as blasting) since it is relat
ed
t
o the stresses that are experienced by buildings and is not used t
o
ev
aluate human res
ponse.
R
oot mean square (rms) velocity – Because the net average of
a
v
ibration signal is zero, the rms amplitude is used to describe smoot
hed
v
ibration amplitude. The rms of a signal is the square root of t
he
FEDERAL TRANSIT ADMINISTRATION 110
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
average of the squared amplitude of the signal. The average is typically
calculated over a one-second period. The rms amplitude is always less
than the PPV
(
viii
)
and is always positive. The rms amplitude is used to
convey the magnitude of the vibration signal felt by the human body, in
inches/second.
Figure 5-2 Vibration Signal in Absolute Units
The PPV and rms velocity are described in inches per second in the United
States and meters per second internationally (with several different reference
values). Although it is not universally accepted, vibration is commonly expressed
in decibel notation. The decibel scale compresses the range of numbers
required to describe vibration.
The graph in Figure 5-3 shows the rms curve from Figure 5-2 expressed in
decibels.
Vibration velocity level in decibels is defined as:
Eq. 5-1
where:
= velocity level, VdB
= rms velocity amplitude
= 1 x 10
-6
in/sec in the USA
= 1 x 10
-8
m/sec internationally
*
*Because of the variations in the reference quantities, it is important to be clear about what
reference quantity is being used when specifying velocity levels. All vibration levels in this
manual are referenced to 1x10
-6
inches/second.
viii
The ratio of PPV to maximum rms amplitude is defined as the crest factor for the signal. The crest factor is typically greater
than 1.41, although a crest factor of 8 or more is not unusual for impulsive signals. For ground-borne vibration from trains, the
crest factor is usually 4 to 5.
FEDERAL TRANSIT ADMINISTRATION 111
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Figure 5-3 Vibration Signal in RMS Velocity Decibels
Ground-borne noise occurs when vibration radiates through a building interior
and creates a low-frequency sound, often described as a rumble, as a train
passes by. The annoyance potential of ground-borne noise is typically
characterized with the A-weighted sound level. Although the A-weighted sound
level is typically used to characterize community noise, characterizing low-
frequency noise using A-weighting can be challenging because the non-linearity
of human hearing causes sounds dominated by low-frequency components to
seem louder than broadband sounds (sounds consisting of many frequency
components, with no dominant frequencies) that have the same A-weighted
level. The result is that ground-borne noise with a level of 40 dBA sounds
louder than 40 dBA broadband noise. Because ground-borne noise sounds
louder than broadband noise at the same noise level, the limits for ground-
borne noise are lower (i.e., stricter) than would be the case for broadband
noise.
5.2 Sources of Transit Ground-borne Vibration
and Noise
Ground-borne vibration can be a concern for nearby neighbors of a transit
system route or maintenance facility. However, in contrast to airborne noise,
ground-borne vibration is not a common environmental problem. It is unusual
for vibration from sources such as buses and trucks to be perceptible, even in
locations close to major roads. This section discusses common sources of
ground-borne vibration and noise.
Most perceptible indoor vibration is caused by sources within buildings such as
operation of mechanical equipment, movement of people, or slamming of doors.
Typical outdoor sources of vibration waves that propagate through the ground
and create perceptible ground-borne vibration in nearby buildings include
construction equipment, steel-wheeled trains, and traffic on rough roads. If the
roadway is fairly smooth, the vibration from rubber-tired traffic is rarely
perceptible. Building damage due to vibration is also rare for typical
transportation projects; but in extreme cases, such as during blasting or pile-
driving during construction, vibration could cause damage to buildings.
Figure 5-4 illustrates common vibration sources and the human and structural
response to ground-borne vibration ranging from approximately 50 VdB (below
FEDERAL TRANSIT ADMINISTRATION 112
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
perceptibility) to 100 VdB (the threshold of potential damage). The background
vibration velocity level in residential areas is usually 50 VdB or lower,
(
ix
)
and the
threshold of perception for humans is approximately 65 VdB. A vibration level
of 85 VdB in a residence can result in strong annoyance.
Figure 5-4 Typical Levels of Ground-Borne Vibration
Rapid transit or light rail systems typically generate vibration levels of 70 VdB or
more near their tracks, while buses and trucks rarely create vibration that
exceeds 70 VdB unless there are bumps due to frequent potholes in the road.
Heavy locomotives on diesel commuter rail systems create vibration levels
approximately 5 to 10 dB higher than rail transit vehicles.
Vibration from trains is strongly dependent on factors such as how smooth the
wheels and rails are, as well as the resonance frequencies of the vehicle
suspension system and the track support system. These systems, like all
mechanical systems, have resonances that result in increased vibration response
at certain frequencies, called natural frequencies. Unusually rough road or track,
steel-wheel flats, geologic conditions that promote efficient propagation of
vibration, or vehicles with very stiff suspension systems could increase typical
ix
Background vibration is typically well below the threshold of human perception and is of concern only when the vibration
affects very sensitive manufacturing or research equipment. Electron microscopes and high-resolution lithography equipment
are examples of equipment that is highly sensitive to vibration.
FEDERAL TRANSIT ADMINISTRATION 113
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
vibration levels by approximately 10 VdB. Common factors that contribute to
ground-borne vibration and noise at the source are presented in Table 5-2.
These factors are discussed in more detail throughout this Section.
Table 5-2 Factors that Influence Levels of Ground-Borne Vibration and Noise at the Source
Category
Factors
Influence
Speed
Higher speeds result in higher vibration levels. Doubling speed results in a
vibration level increase of approximately 4 to 6 dB.
Operations
and
Vehicle
Suspension
Stiff suspension in the vertical direction can increase the effective vibration
forces. On transit cars, the primary suspension has the largest effect on vibration
levels.
Vehicles
Wheel
Condition
and Type
Wheel flats and general wheel roughness are major sources of vibration from
steel wheel/steel rail systems. Resilient wheels on rail transit systems can provide
some vibration reduction over solid steel wheels, but are usually too stiff to
provide substantial reduction. For more information, see Section 6.4, Step 2.
Track/Roadway
Surface
Rough track or rough roads are often sources of excessive vibration. Maintaining
a smooth surface will reduce vibration levels.
Track Support
System
On rail systems, the track support system is one of the major components in
determining the levels of vibration. The highest vibration levels are created by
track that is rigidly attached to a concrete trackbed (e.g., track on wood half-ties
embedded in the concrete). The vibration levels are much lower when special
vibration control track systems such as resilient fasteners, ballast mats, and
floating slabs are used.
Guideway
Transit
Structure
Heavier transit structures typically result in the lower vibration levels. The
vibration levels from a lightweight bored tunnel will usually be higher than from a
poured concrete box subway.
Transit System
Elevation
A rail system guideway will be either underground (subway), at-grade, or
elevated, with substantial differences in the vibration characteristics at each
elevation.
Underground: vibration is typically the most important environmental
factor of interest.
At-grade: airborne noise is typically the dominant factor, although vibration
and noise can be a problem, particularly at interior locations well isolated
from exterior noise.
Elevated: it is rare for vibration to be an issue with elevated railways
except when guideway supports are located within 50 ft of buildings.
Brief discussions of ground-borne vibration and noise sources for different
modes of transit are provided below.
At-Grade Heavy Rail and Light Rail
Ground-borne vibration and noise from urban heavy rail and LRT is common
when there is less than 50 ft between the track and building foundations. Local
geology and structural details of the building determine if the source of
complaints is due to perceptible vibration or audible ground-borne noise.
Complaints about ground-borne vibration from surface track are more common
than ground-borne noise complaints. A substantial percentage of complaints
about both ground-borne vibration and noise correlate with proximity of special
track work, rough or corrugated track, or wheel flats. Light rail systems tend to
generate fewer complaints than heavy rail due to lower operating speeds.
FEDERAL TRANSIT ADMINISTRATION 114
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Commuter and Intercity Passenger Trains
There is the potential for vibration-related issues when new commuter or
intercity rail passenger service (including electric multiple units (EMUs) and
diesel multiple units (DMUs)) powered by either diesel or electric locomotives
is introduced in an urban or suburban area. Commuter and intercity passenger
trains have similar characteristics, but commuter trains typically operate on a
more frequent schedule. These passenger trains often share track with freight
trains, which have different vibration characteristics as discussed below.
Freight Trains
Local and long-distance freight trains are similar in that they both are diesel-
powered and have the same types of cars. They differ in their overall length,
number and size of locomotives, and number of heavily loaded cars. However,
because locomotive suspensions are similar, the maximum vibration levels of
local and long-distance freights are similar. Locomotives and rail cars with wheel
flats are the sources of the highest vibration levels.
If the transit project does not in any way change the freight service, tracks, etc.,
then vibration from the freight line would be part of the existing conditions and
need to be considered in terms of cumulative impacts (see Section 6.2, Step 3
on how to consider cumulative impacts). If the project results in changes to the
freight path, operations, frequency, etc. (e.g., relocating freight tracks within the
ROW to make room for the transit tracks) then those potential impacts and
mitigation should be evaluated as part of the proposed project. However, note
that vibration mitigation is very difficult to implement on tracks where freight
trains with heavy axle loads operate.
High-Speed Passenger Trains
Passenger trains travelling at high speeds, 90 to 250 miles per hour, have the
potential for creating high levels of ground-borne vibration. Ground-borne
vibration should be anticipated as one of the major environmental impacts of
any trains travelling at high speeds located in an urban or suburban area.
(
x
)
For
projects that are specifically high-speed transportation refer to the FRA “High-
Speed Ground Transportation Noise and Vibration Impact Assessment”
guidance manual.
(
39
)
AGT Systems
AGT systems include a wide range of transportation vehicles that provide local
circulation in downtown areas, airports, and theme parks. Because AGT
systems normally operate at low speeds, have lightweight vehicles, run on
elevated structures, and rarely operate in vibration-sensitive areas, ground-
borne vibration problems are very rare.
Subway and At-grade Track
While ground-borne vibration produced from trains operating subway and at-
grade track have very different characteristics, they have comparable overall
vibration velocity levels. Complaints about ground-borne vibration are often
more common near subways than near at-grade track. This is not because
x
Amtrak trains (branded Acela at the time of publication) on the Northeast Corridor between Boston and Washington, DC,
which attain moderate to high speeds in some sections with improved track, fit into this category.
FEDERAL TRANSIT ADMINISTRATION 115
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
subways create higher vibration levels than at-grade systems, rather because
subways are usually located in more densely developed areas in closer proximity
to building foundations, and the airborne noise is usually a more serious
problem for at-grade systems than the ground-borne vibration. Another
difference between subway and at-grade track is that the ground-borne
vibration from subways tends to be higher frequency than the vibration from at-
grade track, which makes the ground-borne noise more noticeable.
Streetcars
Complaints about ground-borne vibration from street cars are uncommon given
that streetcars typically operate at very low speeds (less than 25 mph).
Buses
Because the rubber tires and suspension systems of buses provide vibration
isolation, it is unusual for buses to cause ground-borne vibration or noise
problems. For most issues with bus-related vibration, such as rattling of
windows, the cause is almost always airborne noise and directly related to
running surface conditions such as potholes, bumps, expansion joints, or other
discontinuities in the road surface (usually resolved by smoothing the
discontinuities).
Buses operating inside buildings will likely cause vibration concerns for other
building inhabitants. An example of this situation is a bus transfer station in the
same building as commercial office space. Sudden loading of a building slab by a
heavy moving vehicle or by vehicles running over lane divider bumps can cause
intrusive building vibration.
5.3 Paths of Transit Ground-Borne Vibration and
Noise
Vibration travels from the source through the transit structure and excites the
adjacent ground, creating vibration waves that propagate through soil layers and
rock strata to the foundations of nearby buildings. The vibration then
propagates from the foundation throughout the remainder of the building
structure. The vibration of the building structure and room surfaces can radiate
a low-frequency rumble called ground-borne noise (Figure 5-1).
Soil and subsurface conditions are known to have a strong influence on the
levels of ground-borne vibration. Among the most important factors are the
stiffness and internal damping of the soil and the depth to bedrock. Vibration
propagation is more efficient in stiff clay soils. Shallow rock may concentrate the
vibration energy close to the surface, resulting in ground-borne vibration
problems at large distances from the track. Factors such as soil layers and depth
to water table can have substantial effects on the propagation of ground-borne
vibration. These factors are summarized in Table 5-3.
FEDERAL TRANSIT ADMINISTRATION 116
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Table 5-3 Factors that Influence Levels of Ground-borne Vibration and Noise along Path
Geology Factors
Influence
Soil type
Vibration levels are generally higher in stiff clay-type soil than in loose sandy soil.
Rock layers
Vibration levels are usually high near at-grade track when the depth to bedrock is 30 ft
or less. Subways founded in rock will result in lower vibration amplitudes close to the
subway. Vibration levels do not attenuate as rapidly in rock as in soil.
Soil layering
Soil layering can have a substantial effect on the vibration levels since each stratum can
have considerably different dynamic characteristics.
Depth to water table
The presence of the water table may have a substantial effect on vibration, but a
definite relationship has not been established.
5.4 Receiver Factors that Influence Ground-
Borne Vibration and Noise
Ground-borne vibration is a concern almost exclusively inside buildings. Train
vibration may be perceptible to people who are outdoors, but it is very rare for
outdoor vibration to cause complaints.
The vibration levels inside a building are dependent on the vibration energy that
reaches the building foundation, coupling of the building foundation to the soil,
and propagation of the vibration through the building. In general, the heavier a
building is, the lower the response will be to the incident vibration energy.
Common factors that contribute to ground-borne vibration and noise at the
receiver are presented in Table 5-4.
Table 5-4 Factors that Influence Levels of Ground-Borne Vibration and Noise at the Receiver
Receiver Building
Factors
Influence
Foundation type
The heavier the building foundation, the greater the coupling loss as the vibration
propagates from the ground into the building.
Building
construction
Each building has different characteristics relative to structure-borne vibration, but, in
general, the heavier the building, the lower the levels of vibration. The maximum
vibration amplitudes of the floors and walls of a building will often occur at the
resonance frequencies of the components of the building.
Acoustical
absorption
The more acoustically absorptive materials in the receiver room, the lower the
ground-borne noise level. Note that because ground-borne noise usually is a low-
frequency phenomenon, it is affected by low-frequency absorption (e.g., below 250
Hz).
5.5 Human Response to Transit Ground-borne
Vibration and Noise
This section contains an overview of human receiver response to ground-borne
vibration and noise. It serves as background information for the vibration impact
criteria in Section 6.2.
The effects of ground-borne vibration can include perceptible movement of
floors in buildings, rattling of windows, shaking of items on shelves or hanging on
walls, and low-frequency noise (ground-borne noise). Building damage is not a
FEDERAL TRANSIT ADMINISTRATION 117
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
factor for typical transportation projects, but in extreme cases, such as during
blasting or pile-driving during construction, vibration could cause damage to
buildings. Although the perceptibility threshold is approximately 65 VdB, human
response to vibration is not usually substantial unless the vibration exceeds 70
VdB (Figure 5-4). A vibration level that causes annoyance is well below the
damage risk threshold for typical buildings (100 VdB).
Ground-borne vibration is almost never a problem outdoors. Although the
motion of the ground may be perceived, without the effects associated with the
shaking of a building, the motion does not provoke the same adverse human
reaction. Ground-borne noise that accompanies the building vibration is usually
perceptible only inside buildings and typically is only an issue at locations with
subway or tunnel operations where there is no airborne noise path or for
buildings with substantial sound insulation such as a recording studio.
One of the challenges in developing suitable criteria for ground-borne vibration
is that there has been relatively little research into human response to vibration
and, specifically, human annoyance with building vibration. The American
National Standards Institute (ANSI) developed criteria for evaluation of human
exposure to vibration in buildings in 1983,
(
40
)
and the International Organization
for Standardization (ISO) adopted similar criteria in 1989
(
41
)
and revised them in
2003.
(
42
)
The 2003 version of ISO 2631-2 acknowledges that “human response
to vibration in buildings is very complex.” It further indicates that the degree of
annoyance cannot always be explained by the magnitude of the vibration alone.
In some cases, complaints are associated with measured vibration that is lower
than the perception threshold. Other phenomena such as ground-borne noise,
rattling, visual effects such as movement of hanging objects, and time of day (e.g.,
late at night) all play some role in the response of individuals. To understand and
evaluate human response, which is often measured by complaints, all of these
related effects need to be considered.
Figure 5-5 illustrates the relationship between the vibration velocity level
measured in 22 homes and the general response of the occupants to the
vibration from measurements performed for several transit systems along with
subjective ratings by researchers and residents. These data are published in the
“State-of-the-Art Review of Ground-borne Noise and Vibration.”
(
43
)
The figure
also includes a curve representing the percent of people annoyed by vibration
from high-speed trains from a Japanese study for comparison.
(
44
)
Both the occupants and the people who performed the measurements agreed
that floor vibration in the Distinctly Perceptible range is unacceptable for a
residence. The data indicates that residential vibration exceeding 75 VdB is
unacceptable for a repetitive vibration source such as rapid transit trains that
pass every 5 to 15 minutes. The results from the Japanese study confirm the
conclusion that at a vibration velocity level of 75 to 80 VdB, many people will
find the vibration annoying. A Transportation Research Board (TRB) study of
human response to vibration from 2009 also supports this finding and indicates
that incidence of complaints fall rapidly with a level decreasing below 72
VdB.
(42)(
45
)
FEDERAL TRANSIT ADMINISTRATION 118
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Response to Rapid
Transit Trains
Range of Response to
Rapid Transit Trains
Response to High-
Speed Trains
Figure 5-5 Response to Transit-Induced Residential Vibration
Table 5-5 presents the human response to different levels of ground-borne
vibration and noise on which the criteria presented in Section 6.2 are based.
The vibration level (VdB) is presented with the corresponding frequency
assuming that the vibration spectrum peaks at 30 Hz or 60 Hz.
(
xi
)
The ground-
borne noise levels (dBA) are estimated for the specified vibration velocity with a
peak vibration spectrum of 30 Hz (Low Freq) and 60 Hz (Mid Freq). Note that
the human response differs for vibration velocity level based on frequency. For
example, the noise caused by vibrating structural components may cause
annoyance even though the vibration cannot be felt. Alternatively, a low-
frequency vibration can cause annoyance while the ground-borne noise level it
generates does not.
xi
The A-weighted level of ground-borne noise can be estimated by applying A-weighting to the vibration velocity spectrum and
by subtracting an additional 5 dB for a room with average acoustical absorption. Since the A-weighting at 31.5 Hz is -39.4 dB, if
the vibration spectrum peaks at 30 Hz, the A-weighted sound level will be approximately 40 dB lower than the velocity level. If
the vibration spectrum peaks at 60 Hz, the A-weighted sound level will be approximately 25 dB lower than the velocity level.
FEDERAL TRANSIT ADMINISTRATION 119
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Table 5-5 Human Response to Different Levels of Ground-Borne Vibration and Noise
Vibration
Velocity Level
Noise Level
Human Response
Low
Freq*
Mid
Freq**
65 VdB
25 dBA
40 dBA
Approximate threshold of perception for many humans. Low-
frequency sound: usually inaudible. Mid-frequency sound: excessive
for quiet sleeping areas.
75 VdB
35 dBA
50 dBA
Approximate dividing line between barely perceptible and distinctly
perceptible. Many people find transit vibration at this level annoying.
Low-frequency noise: tolerable for sleeping areas. Mid-frequency
noise: excessive in most quiet occupied areas.
85 VdB
45 dBA
60 dBA
Vibration tolerable only if there are an infrequent number of events
per day. Low-frequency noise: excessive for sleeping areas. Mid-
frequency noise: excessive even for infrequent events for some
activities.
*Approximate noise level when vibration spectrum peak is near 30 Hz.
**Approximate noise level when vibration spectrum peak is near 60 Hz.
FEDERAL TRANSIT ADMINISTRATION 120
SECTION
6
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Vibration Impact Analysis
The FTA vibration impact analysis process is a multi-step process used to
evaluate a project for potential vibration impacts. If impact is determined,
measures necessary to mitigate adverse impacts are to be considered for
incorporation into the project.
(3)
The FTA vibration impact analysis steps are summarized as follows and are
described in the following sections:
6.1 Determine vibration analysis level.
6.2 Determine vibration impact criteria.
Option A: General Vibration Assessment Criteria
Option B: Vibration Impact Criteria for a Detailed Vibration Analysis
6.3 Evaluate Impact: Vibration Screening Procedure
Step 1: Classify project vehicles.
Step 2: Determine project type.
Step 3: Determine screening distance.
Step 4: Identify vibration-sensitive land uses.
6.4 Evaluate Impact: General Vibration Assessment.
Step 1: Select base curve for ground surface vibration level.
Step 2: Apply adjustments.
Step 3: Inventory vibration impact.
6.5 Evaluate Impact: Detailed Vibration Analysis
Step 1: Characterize Existing Vibration
Step 2: Estimate Vibration Impact
Step 3: Assess Vibration Impacts
Step 4: Determine Vibration Mitigation Measures
A similar process for the noise impact analysis is presented in Section 4. After
the noise and vibration analyses have been completed, assess construction noise
and vibration according to Section 7 and document findings according to
Section 8.
6.1 Determine Vibration Analysis Level
There are three levels of analysis to assess the potential ground-borne vibration
and noise impacts resulting from a public transportation project. The
appropriate level of analysis varies by project based on the type and scale of the
project, the stage of project development, and its environmental setting. These
three levels are: the Vibration Screening Procedure, the General Vibration
Assessment, and the Detailed Vibration Analysis. These levels of vibration
analysis mirror the levels of noise analysis discussed in Section 4.2.
The Vibration Screening Procedure, performed first, defines the study area of
any subsequent vibration impact assessment. Where there is potential for
FEDERAL TRANSIT ADMINISTRATION 121
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
impact, the General Vibration Assessment and Detailed Vibration Analysis
procedures are used to determine the extent and severity of impact. In some
cases, a General Vibration Assessment may be all that is needed. However, if
the proposed project is near noise-sensitive land uses and it appears at the
outset that the impact would be substantial, it is prudent to conduct a Detailed
Vibration Analysis.
The methods for analyzing transit vibration are consistent with those described
in recognized handbooks and international standards.
(
46
)(
47
)
Conduct the vibration screening procedure and then determine the appropriate
vibration analysis option:
Vibration Screening Procedure – The Vibration Screening Procedure is a
simplified method of identifying the potential for vibration impact from transit
projects. The Vibration Screening Procedure is applicable to all types of transit
projects and does not require any specific knowledge about the vibration
characteristics of the system or the geology of the area. This procedure uses
simplified assumptions and considers the type of project and the presence or
absence of vibration-sensitive land uses within a screening distance that has been
developed to identify most potential vibration impacts. If no vibration-sensitive
land uses are present within the defined screening distance, then no further
vibration assessment is necessary.
The Vibration Screening Procedure steps are provided in Section 6.3, Step 1.
General Vibration Assessment – The General Vibration Assessment is used
to examine potential impacts to vibration-sensitive land use areas identified in
the screening step more closely. It uses generalized information likely to be
available at an early stage in the project development process and during the
development of most environmental documents.
Vibration levels at receivers are determined by estimating the overall vibration
velocity level and A-weighted ground-borne noise levels as a function of distance
from the track and applying adjustments to account for factors such as track
support systems, vehicle speed, type of building, and track and wheel conditions.
A General Vibration Assessment is sufficient for the environmental review of
many projects, including projects that compare transit modal alternatives or
relocate a crossover or turnout. The General Vibration Assessment may also be
sufficient if it results in a commitment to mitigation that eliminates the vibration
impacts, such as a change in transit mode or alignment. However, if impact is
identified through the General Vibration Assessment procedures and not
mitigated, a Detailed Vibration Analysis of the selected alternative must be
completed. Most vibration mitigation measures can only be specified after a
Detailed Vibration Analysis has been done.
The General Vibration Assessment procedure is provided in Section 6.3, Step 2.
Detailed Vibration Analysis – The Detailed Vibration Analysis procedure is a
comprehensive assessment method that produces the most accurate estimates
FEDERAL TRANSIT ADMINISTRATION 122
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
of vibration impact for a proposed project and is often accomplished during the
engineering phase of a project when there are sufficient data identifying
potential adverse vibration impacts from the project. However, a Detailed
Vibration Analysis may be warranted earlier in the environmental review
process if there are potentially severe impacts due to the proximity of vibration-
sensitive land uses. This type of assessment requires professionals with
experience in performing and interpreting vibration propagation tests.
A Detailed Vibration Analysis may not be necessary for all segments of a
project. Generalized prediction curves from the General Vibration Assessment
procedures may be sufficient for most of the alignment, and the Detailed
Vibration Analysis procedure may only need to be applied to particularly
sensitive receivers (Section 6.3). Note that a Detailed Vibration Analysis is
typically required when designing special track-support systems such as floating
slabs or ballast mats. These and other costly vibration mitigation measures can
only be specified after a Detailed Vibration Analysis has been done in the
engineering phase of the project.
The Detailed Vibration Analysis procedure is presented in Section 6.3, Step 3.
6.2 Determine Vibration Impact Criteria
Use the FTA criteria presented in this section when conducting a General
Vibration Assessment or a Detailed Vibration Assessment. Like noise, the
sensitivity to vibration varies by land use type, and the criteria represent these
sensitivities. These criteria are based on national and international
(38)(39)(
48
)
standards, as well as experience on human response to building
vibration. See Section 5.5 for additional background information on the
development of FTA vibration criteria. The criteria for environmental impact
from ground-borne vibration and noise are based on the maximum root-
mean-square (rms) vibration velocity levels for repeated events of the same
source.
Determine the appropriate criteria based on the level of analysis (Section 6.1).
The impact criteria for the General Vibration Assessment are presented in
Option A, and the impact criteria for the Detailed Vibration Analysis are
presented in Option B.
Option A: General Vibration Assessment Criteria
Determine the land use according to Step 1 and the frequency of events
according to Step 2. The impact criteria for the General Vibration Analysis are
presented in Step 3.
Step 1: Land Use Categories
Determine the appropriate land use category for the receiver of vibration impacts of
the project or project segment. Sensitive land use categories for vibration
assessment are presented in Table 6-1 in order of sensitivity. Consider indoor
use of the buildings when determining land use categories for ground-borne
vibration and noise, since impact is experienced indoors.
FEDERAL TRANSIT ADMINISTRATION 123
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Table 6-1 Land Use Categories for General Vibration Assessment Impact Criteria
Land Use
Category
Land Use
Type
Description of Land Use Category
-
Special
Buildings
This category includes special-use facilities that are very sensitive to vibration and
noise that are not included in the categories below and require special consideration.
However, if the building will rarely be occupied when the source of the vibration
(e.g., the train) is operating, there is no need to evaluate for impact. Examples of
these facilities include concert halls, TV and recording studios, and theaters.
1
High
Sensitivity
This category includes buildings where vibration levels, including those below the
threshold of human annoyance, would interfere with operations within the building.
Examples include buildings where vibration-sensitive research and manufacturing* is
conducted, hospitals with vibration-sensitive equipment, and universities conducting
physical research operations. The building’s degree of sensitivity to vibration is
dependent on the specific equipment that will be affected by the vibration.
Equipment moderately sensitive to vibration, such as high resolution lithographic
equipment, optical microscopes, and electron microscopes with vibration isolation
systems are included in this category.** For equipment that is more sensitive, a
Detailed Vibration Analysis must be conducted.
2
Residential
This category includes all residential land use and buildings where people normally
sleep, such as hotels and hospitals. Transit-generated ground-borne vibration and
noise from subways or surface running trains are considered to have a similar effect
on receivers.***
3
Institutional
This category includes institutions and offices that have vibration-sensitive equipment
and have the potential for activity interference such as schools, churches, doctors’
offices. Commercial or industrial locations including office buildings are not included
in this category unless there is vibration-sensitive activity or equipment within the
building. As with noise, the use of the building determines the vibration sensitivity.
* Manufacturing of computer chips is an example of a vibration-sensitive process.
** Standard optical microscopes can be impacted at vibration levels below the threshold of human annoyance.
*** Even in noisy urban areas, the bedrooms will often be in quiet buildings with effective noise insulation. However, ground-
borne vibration and noise are experienced indoors, and building occupants have practically no means to reduce their
exposure. Therefore, occupants in noisy urban areas are just as likely to be exposed to ground-borne vibration and noise
as those in quiet suburban areas.
Ground-borne Vibration – Locations with equipment that is highly-
sensitive to vibration should be included in category 1 or assessed using the
Detailed Vibration Analysis procedures (Section 6.3, Step 3) and criteria
(Section 6.2, Option B) or specific criteria of the equipment manufacturer.
Most computer installations or telephone switching equipment is not
considered sensitive to vibration. Although the owners of this type of
equipment often are concerned with the potential for ground-borne
vibration interrupting smooth operation of their equipment, it is rare for
computer or other electronic equipment to be particularly sensitive to
vibration. This type of equipment is typically designed to operate in
common building environments where the equipment may experience
occasional disturbances and continuous background vibration caused by
other equipment.
Ground-borne Noise – Ground-borne noise is typically only assessed at
locations with subway or tunnel operations where there is no airborne
noise path, or for buildings with substantial sound insulation such as a
recording studio. For typical buildings with at-grade or elevated transit
operations, the interior airborne noise levels are often higher than the
FEDERAL TRANSIT ADMINISTRATION 124
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
ground-borne noise levels. For interior rooms or other special cases,
ground-borne noise may need to be assessed.
Step 2: Identify Event Frequency
Determine the appropriate frequency of events for the project or project segment.
Community response to vibration correlates with the frequency of events and,
intuitively, more frequent events of low vibration levels may evoke the same
response as fewer high vibration level events. This effect is accounted for in the
ground-borne vibration and noise impact criteria by characterizing projects by
frequency of events. Event frequency definitions are presented in Table 6-2.
Table 6-2 Event Frequency Definitions
Category
Definition
Typical Project Types
Frequent Events
More than 70 events per day
Most rapid transit
Occasional Events
30–70 events per day
Most commuter trunk lines
Infrequent Events
Fewer than 30 events per day
Most commuter rail branch lines
Step 3: Apply Impact Criteria by Land Use and Event
Frequency
Select the appropriate impact criteria for ground-borne vibration and noise
based on the previously identified land use categories and frequency of events. It
is also important to consider the time of vibration sensitivity. If the building is
not typically occupied when the vibration source (e.g., train) is operating, it is
not necessary to consider impact.
The criteria in this section are appropriate for assessing human annoyance or
interference with vibration-sensitive equipment for common projects. While not
typical, existing conditions, freight train operations, and building damage may
require consideration.
Existing Conditions – The criteria in this section do not consider exist
ing
conditions. In most cases, the existing environment does not include a
s
ubstantial number of perceptible ground-borne vibration or noise events
.
However, existing conditions must be evaluated in some cases, such as for
pr
ojects located in an existing rail corridor. For criteria considering exist
ing
c
onditions, see Step 3b
.
F
reight Train Operations – The criteria are primarily based
on
exper
ience with passenger train operations. Passenger train operat
ions
(
rapid transit, commuter rail, and intercity passenger railroad) creat
e
v
ibration events that last approximately 10 seconds or less while a typica
l
li
ne-haul freight train event lasts approximately two minutes. This manual
is
ori
ented to transit projects. However, situations will occur when freig
ht
t
rain operations must be evaluated, such as when freight train tracks ar
e
r
elocated for a transit project within a railroad ROW. Guidelines
on
applying these criteria to freight train operations are presented in Step 3c.
FEDERAL TRANSIT ADMINISTRATION 125
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Building Damage – It is extremely rare for vibration from train
operations to cause substantial or even minor cosmetic building damage.
However, damage to fragile historic buildings located near the ROW may be
of concern. Even in these cases, damage is unlikely except when the track is
located very close to the structure. Damage thresholds that apply to these
structures are discussed in Section 7.2, Step 4 on Construction Vibration
Impacts.
3a. Choose the impact criteria by land use category and event
frequency. The criteria for ground-borne vibration and noise land use
categories 1-3 are presented in Table 6-3. The criteria are presented in terms of
acceptable indoor ground-borne vibration and noise levels. Impact will occur if
these levels are exceeded. Criteria for ground-borne vibration are expressed in
terms of rms velocity levels in VdB, and criteria for ground-borne noise are
expressed in terms of A-weighted sound pressure levels in dBA.
Table 6-3 Indoor Ground-Borne Vibration (GBV) and Ground-Borne Noise (GBN)
Impact Criteria for General Vibration Assessment
Land Use Category
GBV Impact Levels
(VdB re 1 micro-inch /sec)
GBN Impact Levels
(dBA re 20 micro Pascals)
Frequent
Events
Occasional
Events
Infrequent
Events
Frequent
Events
Occasional
Events
Infrequent
Events
Category 1: Buildings where
vibration would interfere with
interior operations.
65 VdB
*
65 VdB
*
65 VdB
*
N/A
**
N/A
**
N/A
**
Category 2: Residences and
buildings where people
normally sleep.
72 VdB
75 VdB
80 VdB
35 dBA
38 dBA
43 dBA
Category 3: Institutional land
uses with primarily daytime
use.
75 VdB
78 VdB
83 VdB
40 dBA
43 dBA
48 dBA
* This criterion limit is based on levels that are acceptable for most moderately sensitive equipment such as optical
microscopes. For equipment that is more sensitive, a Detailed Vibration Analysis must be performed.
** Vibration-sensitive equipment is generally not sensitive to ground-borne noise; however, the manufacturer’s
specifications should be reviewed for acoustic and vibration sensitivity.
The criteria for ground-borne vibration and noise for special land uses are
presented in Table 6-4. The criteria are presented in terms of acceptable indoor
ground-borne vibration and noise levels. Impact will occur if these levels are
exceeded. As for the other land uses, the criteria for ground-borne vibration
are expressed in terms of rms velocity levels in VdB, and criteria for ground-
borne noise are expressed in terms of sound pressure levels in dBA.
Table 6-4 Indoor Ground-Borne Vibration and Noise Impact Criteria for Special Buildings
Type of Building or
Ground-Borne Vibration Impact
Levels (VdB re 1 micro-inch/sec)
Ground-Borne Noise Impact
Levels (dBA re 20 micro-Pascals)
Room
Frequent
Events
Occasional or
Infrequent Events
Frequent
Events
Occasional or
Infrequent Events
Concert halls
65 VdB
65 VdB
25 dBA
25 dBA
TV studios
65 VdB
65 VdB
25 dBA
25 dBA
Recording studios
65 VdB
65 VdB
25 dBA
25 dBA
Auditoriums
72 VdB
80 VdB
30 dBA
38 dBA
Theaters
72 VdB
80 VdB
35 dBA
43 dBA
FEDERAL TRANSIT ADMINISTRATION 126
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
3b. Consider the presence of existing vibration conditions.
When the project will cause vibration more than 5 dB above the existing
vibration, the existing source can be ignored, and the standard vibration
criteria in Step 3a are appropriate. When the project will cause vibration less
than 5 dB above the existing vibration level, use the instructions presented in
this section to determine the appropriate impact criteria for the project. For
information on characterizing existing vibration conditions, see Section 6.2,
Step 3.
Use Table 6-5 and Figure 6-1 to determine the appropriate impact criteria.
Sources of existing vibration are typically longer in duration than the events
introduced into the environment due to the project. The frequency of use in the
rail corridor is also a factor in characterizing the existing conditions. Both
factors are considered in the process of determining appropriate impact criteria
in Table 6-5 and Figure 6-1.
Examples of projects considering the existing vibration conditions in Table 6-5
and Figure 6-1 include:
An automated people mover system planned for a corridor with an
existing rapid transit service with 220 trains per day that did not have a
significant increase in events from the existing 220 trains per day and
that is not 3 dB above the existing vibration level would cause no
additional impact.
Where a new commuter rail line shares a heavily-used corridor with a
rapid transit system, the project vibration exceeds the existing vibration
level, there is not a significant increase in the number of events, and the
project vibration exceeds the existing vibration level by 3 dB or more,
the projected vibration levels must be evaluated using the standard
impact criteria to determine impact.
If a new transit project will use an existing railroad ROW and the
location of existing railroad tracks are shifted, existing vibration can be
substantial. The track relocation and reconstruction can result in lower
vibration levels that would benefit the receivers and not introduce any
adverse impact. However, if the track relocation causes higher vibration
levels at vibration-sensitive receivers, then the projected vibration levels
must be evaluated using the standard impact criteria to determine
impact.
FEDERAL TRANSIT ADMINISTRATION 127
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Table 6-5 Impact Criteria Considering Existing Conditions
Category
Number of Operations
(At present – without project)
Criteria
Heavily
Used
More than 12 trains per day
Use the standard vibration criteria in Section 6.2, Step 3a for the
following scenarios:
The existing vibration does not exceed the standard
vibration criteria.
The existing vibration exceeds the standard vibration criteria
and there is a significant increase in events.*
The existing vibration exceeds the standard vibration
criteria, and the project vibration is 3 dB or more above the
existing vibration.
The project has no impact if the existing vibration exceeds the
standard vibration criteria, the number of events does not increase
significantly, and the project vibration does not exceed the existing
vibration by 3 dB or more.
Moderately
Used
5 – 12 trains per day
Use the standard vibration criteria in Section 6.2 Step 3a for the
following scenarios:
The existing vibration does not exceed the standard
vibration criteria.
The existing vibration exceeds the standard vibration
criteria, and the project vibration is not 5 dB or more below
the existing vibration.
The project has no impact if the existing vibration exceeds the
standard vibration criteria and the project vibration is at least 5 dB
below the existing vibration.
Infrequently
Used
Fewer than 5 trains per day
The standard vibration criteria in Section 6.2, Step 3a apply.
* Approximately doubling the number of events is required for a significant increase.
FEDERAL TRANSIT ADMINISTRATION 128
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Figure 6-1 Existing Vibration
xii
Criteria Flow Chart
3c. Apply criteria to freight trains if part of the project.
Use the criteria presented in Step 3a to assess the vibration from freight trains
in shared ROW scenarios because no specific impact criteria exist for freight
railroads. It is important to consider that freight operations occur over
substantially greater distances than passenger train operations and have different
weight and axle loads.
When assessing vibration from freight train operations, consider the locomotive
and rail car vibration separately. Since locomotive vibration lasts for a very short
time, it can be characterized by the infrequent events category in Table 6-2. Rail
car vibration from a typical line-haul freight train usually lasts for several minutes
and can be characterized by the frequent events category in Table 6-2. Note
xii
Vibration is abbreviated as “vib.” in this flowchart.
FEDERAL TRANSIT ADMINISTRATION 129
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
that locomotives often create vibration levels that are 3 to 8 dB higher than
those created by rail cars.
Use good engineering judgment to confirm the approach is reasonable for each
project. For example, some spur rail lines carry very little rail traffic (sometimes
only one train per week) or have short trains, in which case it may not be
necessary to evaluate for impact. If there is uncertainty in how to determine the
appropriate criteria, contact the FTA Regional office.
Decisions to relocate freight tracks closer to vibration-sensitive sites should be
made with the understanding that increased vibration due to freight rail may not
be possible to mitigate. Freight rail vibration may not always be successfully
mitigated by the same methods as rail transit systems.
Option B: Vibration Impact Criteria for a Detailed Vibration
Analysis
Determine the appropriate impact criteria for ground-borne vibration and
ground-borne noise for a Detailed Vibration Analysis.
Step 1: Ground-Borne Vibration
Choose the appropriate criteria based on Figure 6-2 and Table 6-6.
Ground-borne vibration criteria presented in this section are more detailed
than in the General Vibration Assessment. The criteria are based on
international standards for the effects of vibration on people related to
annoyance and interference with activities in buildings
(39)
as well as industry
standards for vibration-sensitive equipment.
(46)
The criteria in this section are
used to assess the potential for interference or annoyance from building
response and to determine performance of vibration reduction methods. Note
that for highly-sensitive equipment, specific vibration criteria provided by the
manufacturer supersede the criteria in this section.
The criteria are presented by category in Figure 6-2 and are defined by
international and industry standards.
(39)(46)
These criteria define limits for
acceptable maximum rms vibration velocity level with a one-second averaging
time at the floor of the receiving building in terms of a one-third octave band
frequency spectrum. Band levels that exceed a particular criterion curve indicate
impact; and therefore, mitigation options should be evaluated considering the
specific frequency range in which the treatment is most effective. Interpretations
of the criteria are presented in Table 6-6.
FEDERAL TRANSIT ADMINISTRATION 130
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Figure 6-2 Criteria for Detailed Vibration Analysis
Table 6-6 Interpretation of Vibration Criteria for Detailed Vibration Analysis
Criterion
Curve
Max Lv,*
VdB
Description of Use
Workshop (ISO)
90
Vibration that is distinctly felt. Appropriate for workshops and similar
areas not as sensitive to vibration.
Office (ISO)
84
Vibration that can be felt. Appropriate for offices and similar areas not as
sensitive to vibration.
Residential Day
(ISO)
78
Vibration that is barely felt. Adequate for computer equipment and low-
power optical microscopes (up to 20X).
Residential Night,
Operating Rooms
(ISO)
72
Vibration is not felt, but ground-borne noise may be audible inside quiet
rooms. Suitable for medium-power optical microscopes (100X) and other
equipment of low sensitivity.
VC-A
66
Adequate for medium- to high-power optical microscopes (400X),
microbalances, optical balances, and similar specialized equipment.
VC-B
60
Adequate for high-power optical microscopes (1000X) and inspection and
lithography equipment to 3-micron line widths.
VC-C
54
Appropriate for most lithography and inspection equipment to 1-micron
detail size.
VC-D
48
Suitable in most instances for the most demanding equipment, including
electron microscopes operating to the limits of their capabilities.
VC-E
42
The most demanding criterion for extremely vibration-sensitive
equipment.
* As measured in 1/3-octave bands of frequency over the frequency range 8 to 80 Hz.
FEDERAL TRANSIT ADMINISTRATION 131
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
In addition to the uses described in Table 6-6, the detailed vibration criteria can
be applied to the three land use categories presented in Table 6-3.
For residential land uses (category 2), use the residential night criterion
curve in Table 6-6.
For institutional uses (category 3), use the residential day criterion
curve in Table 6-6.
For category 1, the specific use of the building should be matched to the
appropriate criterion curve in Table 6-6.
For special buildings, such as those found in Table 6-4, either the criteria
in Table 6-4 or specific criteria presented by the building operator
should be used.
These criteria use a frequency spectrum because vibration-related problems
generally occur due to resonances of the structural components of a building or
vibration-sensitive equipment. Resonant response is frequency-dependent. A
Detailed Vibration Analysis can provide an assessment that identifies potential
problems resulting from resonances.
The detailed vibration criteria are based on generic cases when people are
standing or equipment is mounted on the floor in a conventional manner.
Consequently, the criteria are less stringent at very low frequencies below 8 Hz.
Where special vibration isolation has been provided in the form of pneumatic
isolators, the resonant frequency of the isolation system is very low.
Consequently, in this special case, the curves may be extended flat at lower
frequencies.
Step 2: Ground-borne Noise
Ground-borne noise impacts are assessed based on criteria for human
annoyance and activity interference. The Detailed Vibration Analysis procedure
provides vibration spectra inside a building. To evaluate ground-borne noise,
convert these vibration spectra to sound pressure level spectra in the occupied
spaces using the method described in Section 6.5 and compare to the criteria as
follows:
For residential buildings, use the criteria presented in Table 6-3.
For special buildings listed in Table 6-4, A-weighted noise may not be
sufficient to assess activity interference for a Detailed Vibration Analysis.
Each special building may have a unique specification for acceptable
noise levels and criteria must be determined on a case-by-case basis.
For example, a recording studio may have stringent requirements for
allowable noise in each frequency band.
6.3 Evaluate Impact: Vibration Screening
Procedure
Determine the potential for impact using the Vibration Screening Procedure by
identifying any vibration-sensitive land uses (Table 6-1) within the appropriate
screening distance.
FEDERAL TRANSIT ADMINISTRATION 132
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Figure 6-3 Flow Chart of Vibration Screening Process
Step 1: Classify Project Vehicles
Determine the project type and the next step based on the guidelines below.
Option A: No Vehicles – Transit projects that do not involve vehicles do not
have potential for vibration impact and do not require further analysis (Box A in
Figure 6-3).
Many smaller FTA-funded projects, such as bus terminals, park-and-ride lots,
and station rehabilitation are in this category, and do not require further analysis
of ground-borne vibration impact. However, if track systems are modified (e.g.,
tracks moved or switches modified), proceed to Step 2.
FEDERAL TRANSIT ADMINISTRATION 133
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Option B: Steel-wheeled/Steel-rail Vehicles – Transit projects with steel-
wheeled/steel-rail vehicles have potential for vibration impact (Box B in Figure
6-3); proceed to Step 2. These rail systems include urban rapid transit, LRT
,
c
ommuter rail, and steel-wheel intermediate capacity transit (ICT) systems
.
O
ption C: Rubber-tire Vehicles – For projects that involve rubber-tire
vehicles and do not meet the following conditions, vibration impact is unlikely,
and no further analysis is needed. Proceed to Step 2 for projects that involve
rubber-tire vehicles and meet the following conditions (Box A in Figure 6.3):
Roadway irregularity – Expansion joints, speed bumps, or other
des
ign features that result in unevenness in the road surface can res
ult
in perceptible ground-borne vibration at distances up to 75 ft away.
Operation close to vibration-sensitive buildings – Buses, trucks,
or other heavy vehicles operating close to a vibration-sensitive building
(
within approximately 100 ft from the property line) may impac
t
v
ibration-sensitive activities, such as research that uses electr
on
mic
roscopes or manufacturing of computer chips
.
Vehicles operating within buildings – Special considerations are
oft
en required for shared use facilities where vehicles operate inside
or
directly underneath buildings such bus stations located inside an office
buil
ding com
plex.
Step 2: Determine Project Type
Determine the project type according to Table 6-7.
FEDERAL TRANSIT ADMINISTRATION 134
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Table 6-7 Project Types for Vibration Screening Procedure
Project Type
Number
Project
Type
Description
1
Conventional
Commuter
Railroad
Both locomotives and passenger vehicles create vibration. For commuter
trains, the highest vibration levels are typically created by the locomotives.
Electric commuter rail vehicles create levels of ground-borne vibration that are
comparable to electric rapid transit vehicles.
2
RRT
Ground-borne vibration impact from rapid transit trains is one of the major
environmental issues for new systems. Ground-borne vibration is usually a
major concern for subway operations. It is less common for at-grade and
elevated rapid transit lines to create intrusive ground-borne vibration and
noise since air-borne noise typically dominates.
3
LRT and
Streetcars
The ground-borne vibration characteristics of light rail systems are very similar
to those of rapid transit systems. Because the speeds of light rail systems are
usually lower, typical vibration levels are usually lower. Steel-wheel/steel-rail
AGT is included in either this category or the ICT category depending on the
level of service and train speeds.
4
Intermediate
Capacity
Transit
Because of the low operating speeds of most ICT systems, vibration problems
are not common. However, steel-wheel ICT systems that operate close to*
vibration-sensitive buildings have the potential of causing intrusive vibration.
With a stiff suspension system, an ICT system could create intrusive vibration.
5
Bus and
Rubber-Tire
Transit
Projects
This category encompasses most projects that do not include steel-wheel
trains of some type. Examples include diesel buses, electric trolley buses, and
rubber-tired people movers. Most projects that do not include steel-wheel
trains do not cause vibration impacts.**
*See the screening distances for category 1 land uses in Table 6-8.
** Most complaints about vibration caused by buses and trucks are related to rattling of windows or items hung on the walls.
These vibrations are usually the result of airborne noise and not ground-borne vibration. In the case where ground-borne
vibration is the source of the complaint, the vibration can usually be attributed to irregularities in the road.
Step 3: Determine Screening Distance
Determine the appropriate screening distances based on land use and project type
according to Table 6-8.
The distances are based on the criteria presented in Section 6.3, the procedures
in Section 6.4 assuming normal vibration propagation, and include a 5-dB factor
of safety. Even so, areas with very efficient vibration propagation can have
substantially higher vibration levels.
Because of the 5-decibel safety factor, the screening distances will identify most
of the potentially impacted areas, even for areas with efficient propagation.
However, when there is evidence of efficient propagation, such as previous
complaints about existing transit facilities or a history of problems with
construction vibration, increase the distances in Table 6-8 by a factor of 1.5.
FEDERAL TRANSIT ADMINISTRATION 135
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Table 6-8 Screening Distances for Vibration Assessments
Type of Project
Critical Distance for Land Use Categories
*
Distance from ROW or Property Line, ft
Land Use
Cat. 1
Land Use
Cat. 2
Land Use
Cat. 3
Conventional Commuter Railroad
600
200
120
RRT
600
200
120
LRT and Streetcars
450
150
100
ICT
200
100
50
Bus Projects (if not previously screened out)
100
50
--
*For the Vibration Screening Procedure, evaluate special buildings as follows: Category 1 - concert halls and TV
studios, Category 2 - theaters and auditoriums
Step 4: Identify Vibration-Sensitive Land Uses
Identify all vibration-sensitive land uses (Table 6-1) within the chosen screening
distance. If no vibration-sensitive land uses are identified, no further vibration
analysis is needed. If one or more of the vibration-sensitive land uses are in the
screening distance, complete a General Vibration Assessment (Section 6.4) or a
Detailed Vibration Analysis (Section 6.5).
6.4 Evaluate Impact: General Vibration
Assessment
Evaluate for impact using the General Vibration Assessment procedure if the Vibration
Screening Procedure (Section 6.3) identified vibration-sensitive receivers within the
screening distance of the transit vibration source.
For guidelines on when the General Vibration Assessment is appropriate,
review Section 6.1.
The basic approach for the General Vibration Assessment is to define a curve or
set of curves that predicts the overall ground-borne vibration as a function of
distance from the source, then apply adjustments to these curves to account for
factors such as vehicle speed, geologic conditions, building type, and receiver
location within the building. When the vehicle type is not covered by the curves
included in this section, it will be necessary to define an appropriate curve
either by extrapolating from existing information or performing measurements
at an existing facility.
Step 1: Select Base Curve for Ground Surface Vibration
Level
Select a standard vibration curve to represent general vibration characteristics for the
source.
The curves presented in Figure 6-4 are based on measurements of ground-
borne vibration at representative North American transit systems and can be
used to represent vibration characteristics for standard transportation systems
in the General Vibration Assessment.
FEDERAL TRANSIT ADMINISTRATION 136
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
These curves assume typical ground-borne vibration levels, equipment in good
condition, and speeds of 50 mph for the rail systems and 30 mph for buses.
Adjustments to account for differences in speed and geologic conditions are
included in Step 2.
Select a base curve from Figure 6-4 according to the guidelines in Table 6-9.
Equations for the curves in Figure 6-4 are included in Table 6-10. Additional
considerations for selecting a base curve for systems not included in Table 6-9
are presented below by transit mode.
Table 6-9 Ground Surface Vibration Level Base Curve Descriptions
Curve
Description
Locomotive-Powered
Passenger or Freight Curve
Appropriate for vehicles powered by diesel or electric locomotives including
intercity passenger trains and commuter rail trains.
Rapid Transit or Light Rail
Vehicles Curve
Appropriate for both heavy and light-rail vehicles on at-grade and subway
track.
Rubber-Tired Vehicles Curve
Appropriate for rubber-tire vehicles. These types of vehicles rarely create
ground-borne vibration problems unless there is a discontinuity or bump in
the road that causes the vibration. This curve represents the vibration level
for a typical bus operating on smooth roadway.
Figure 6-4 Generalized Ground Surface Vibration Curves
FEDERAL TRANSIT ADMINISTRATION 137
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Table 6-10 Generalized Ground Surface Vibration Equations
Curve
Equation
Locomotive Powered
Passenger or Freight Curve
Eq. 6-1
Rapid Transit or Light Rail
Vehicles Curve
Eq. 6-2
Rubber-Tired Vehicles Curve
Eq. 6-3
= velocity level, VdB
distance, ft
Considerations for selecting a base curve for different transit modes include:
Intercity passenger trains – Although intercity passenger trains can
be
an important source of environmental vibration, it is rare that t
hey
a
re considered for FTA-funded projects unless a new transit mode us
es
an existing rail alignment. When a new transit line uses an existing rail
a
lignment, changes in the intercity passenger traffic can result in
either
positive or negative impacts. Use the locomotive-powered passenger or
fr
eight curve for intercity passenger trains unless there are specific dat
a
a
vailable on the ground-borne vibration created by the new tra
in
oper
ations
.
L
ocomotive-powered commuter rail – Use the locomotive-
powered passenger or freight curve for all commuter rail syst
em
power
ed by either diesel or electric locomotives
.
Electric multiple unit (EMU) – Use the rapid transit or light rail
vehicles curve for self-powered electric commuter rail trains.
Di
esel multiple unit (DMU) – Self-powered DMUs create vibrat
ion
lev
els somewhere between rapid transit vehicles and locomotive-
powered passenger trains. A vibration curve for DMUs can
be
es
timated by lowering the locomotive-powered passenger or freig
ht
c
urve by 5 dB
.
S
ubway heavy rail or light rail – Use the rapid transit or light ra
il
vehicles curve for subway heavy rail and subway light rail. Although
v
ibrations from subway and at-grade tracks have very differ
ent
characteristics, the overall vibration velocity levels are comparable.
When
applied to subways, the rapid transit or light rail vehicles curv
e
a
ssumes a relatively lightweight bored concrete tunnel in soil. T
he
vibration levels will be lower for heavier subway structures such as cut-
and-cover box structures and stations
.
At-
grade heavy rail or light rail – Use the rapid transit or light ra
il
v
ehicles curve for at-grade heavy rail or light rail. Heavy rail and LR
T
v
ehicles have similar suspension systems and axle loads and creat
e
s
imilar levels of ground-borne vibrat
ion.
FEDERAL TRANSIT ADMINISTRATION 138
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Elevated guideways or aerial structures – Vibration from
operations on an elevated structure is typically not an issue unless the
guideway is supported by a building or located very close to buildings.
Apply the appropriate adjustment for the aerial structures (Section 6.4,
Step 2).
Streetcars – Use the rapid transit or light rail vehicles curve for street
cars.
ICT – Use the rapid transit or light rail vehicles curve for ICT systems
with steel wheels and the rubber-tired vehicles curve for ICT systems
with rubber tires.
Other vehicle types – For less common modes such as magnetically-
levitated vehicles (maglev), monorail, or AGT, use good engineering
judgment to choose a standard curve to best fit the mode or if a new
curve needs to be developed, as a function of distance from the track.
Examples include:
Vibration from a rubber-tire monorail operating on aerial
guideway can be approximated using the rubber-tired vehicles
curve with the appropriate adjustment for the aerial structure
(Section 6.4, Step 2).
Most of the data available on the noise and vibration
characteristics of maglev vehicles comes from high-speed
systems intended for inter-city service. Even though there is no
direct contact between the vehicle and the guideway, the
dynamic loads on the guideway can generate ground-borne
vibration. Measurements on a German high-speed maglev
resulted in ground-borne vibrations at 75 mph which is
comparable to the base curve for rubber-tired vehicles at 30
mph.
(
49
)
Step 2: Apply Adjustments
Apply project-specific adjustments to the standard vibration curve.
Once the base curve has been selected, use the adjustments in the following
instructions to develop project-specific vibration projections at each receiver.
All adjustments are given as single numbers to add to, or subtract from, the
base level.
Adjustments are separated by source, path, and receiver and include speed,
wheel and rail type and condition, type of track support system, type of building
foundation, and number of floors above the basement level. Calculate the
appropriate adjustments to the base level. An example of the General Vibration
Assessment is provided at the end of this Section.
It should be recognized that many of these adjustments are strongly dependent
on the frequency spectrum of the vibration source and the frequency
dependence of the vibration propagation. The adjustments in this section are
suitable for generalized evaluation of the vibration impact and vibration
FEDERAL TRANSIT ADMINISTRATION 139
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
mitigation measures because they are based on typical vibration spectra.
However, these adjustments are not adequate for detailed evaluations of impact
of vibration-sensitive buildings or for detailed specification of mitigation
measures.
2a. Apply source adjustments to the base curve using Table 6-11 and the
descriptions below to account for the project-specific source characteristics.
Table 6-11 Source Adjustment Factors for Generalized Predictions of GB Vibration and Noise
Source
Factor
Adjustment to
Propagation Curve
Comment
Speed
Vehicle
Speed
60 mph
50 mph
40 mph
30 mph
20 mph
Reference Speed
50 mph
30 mph
+1.6 dB
+6.0 dB
0.0 dB
+4.4 dB
-1.9 dB
+2.5 dB
-4.4 dB
0.0 dB
-8.0 dB
-3.5 dB
Vibration level is approximately proportional to
20log(speed/speed
ref
), see Eq. 6-4.
Vehicle Parameters (not additive, apply greatest value only)
Vehicle with
stiff primary
suspension
+8 dB
Transit vehicles with stiff primary suspensions have been
shown to create high vibration levels. Include this
adjustment when the primary suspension has a vertical
resonance frequency greater than 15 Hz.
Resilient
Wheels
0 dB
Resilient wheels do not generally affect ground-borne
vibration except at frequencies greater than about 80
Hz.
Worn Wheels
or Wheels with
Flats
+10 dB
Wheel flats or wheels that are unevenly worn can cause
high vibration levels.
Track Conditions (not additive, apply greatest value only)
Worn or
Corrugated
Track
+10 dB
Corrugated track is a common problem. Mill scale* on
new rail can cause higher vibration levels until the rail
has been in use for some time. If there are adjustments
for vehicle parameters and the track is worn or
corrugated, only include one adjustment.
Special
Trackwork
within 200 ft
+10 dB (within 100 ft)
+5 dB (between 100 and 200 ft)
Wheel impacts at special trackwork will greatly increase
vibration levels. The increase will be less at greater
distances from the track. Do not include an adjustment
for special trackwork more than 200 ft away.
Jointed Track
+5 dB
Jointed track can cause higher vibration levels than
welded track.
Uneven Road
Surfaces
+5 dB
Rough roads or expansion joints are sources of
increased vibration for rubber-tire transit.
Track Treatments (not additive, apply greatest value only)
Floating Slab
Trackbed
-15 dB
The reduction achieved with a floating slab trackbed is
strongly dependent on the frequency characteristics of
the vibration.
Ballast Mats
-10 dB
Actual reduction is strongly dependent on frequency of
vibration.
High-Resilience
Fasteners
-5 dB
Slab track with track fasteners that are very compliant in
the vertical direction can reduce vibration at frequencies
greater than 40 Hz.
*Mill scale on a new rail is a slightly corrugated condition caused by certain steel mill techniques.
FEDERAL TRANSIT ADMINISTRATION 140
Eq. 6-4
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
In addition to the comments in Table 6-11, use the following guidelines to select
the appropriate adjustment factors. Some adjustments in the same category are
not cumulative (additive) and only the greatest applicable adjustment should be
applied. The adjustments that are not additive are noted in Table 6-11 and in the
descriptions below. Note that some adjustments are not additive across
multiple categories and are noted in the comments of Table 6-11. For example,
the adjustment for a vehicle with stiff primary suspension is 8 dB, and the
adjustment for wheel flats is 10 dB. If the vehicle has a stiff primary suspension
and has wheel flats, the projected vibration levels should be increased by 10 dB,
not 18 dB.
In addition, some vibration control measures are targeted for specific frequency
ranges. The shape of the actual vibration spectra should be considered so that
an appropriate vibration control measure may be selected.
Speed – The levels of ground-borne vibration and noise vary,
a
pproximately, as 20 times the logarithm of speed. This means tha
t
do
ubling train speed will increase the vibration levels approximately
6
dB,
and halving train speed will reduce the levels by 6 dB. T
he
a
djustments in Table 6-11 have been tabulated for reference vehic
le
s
peeds of 30 mph for rubber-tired vehicles and 50 mph for steel-whee
l
v
ehicles. Use the following relationship to calculate the adjustments f
or
ot
her speeds
.
Variation with speed has been observed to be as low
as , but unless specific speed data for vibration for a
vehicle has been obtained, use Eq. 6-4.
Vehicle Parameters – The most important factors for the vehicles
a
re the suspension system, wheel condition, and wheel type. Most
new
heavy rail and light rail vehicles have relatively soft primary suspensions.
Howev
er, a stiff primary suspension (vertical resonance frequenc
y
g
reater than 15 Hz) can result in higher levels of ground-borne vibrat
ion
t
han soft primary suspensions. Vehicles, for which the primar
y
s
uspension consists of rubber or neoprene around the axle bearing
,
us
ually have a very stiff primary suspension with a vertical resonanc
e
fr
equency greater than 40 Hz or more
.
Det
eriorated wheel condition is another factor that increases vibration
levels. It can be assumed that a new system has vehicles with wheels in
good condition. When older vehicles are used on new track, it is
important to consider the condition of the wheels, and it may be
appropriate to include an adjustment for the wheel condition.
Resilient wheels will reduce vibration levels at frequencies greater than
the effective resonance frequency of the wheel. When this resonance
FEDERAL TRANSIT ADMINISTRATION 141
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
frequency is relatively high, greater than 80 Hz, resilient wheels may
only have a marginal effect on ground-borne vibration.
The adjustments in this category are not additive; apply the greatest
applicable value only.
Track Conditions – This category includes the type of rail (wel
ded,
joint
ed, or special trackwork), the track support system, and t
he
c
ondition of the rail. The base curves assume welded rail in goo
d
c
ondition. Jointed rail causes higher vibration levels than welded rail a
nd
the increase depends on the condition of the joints.
Wheel impacts at special trackwork, such as frogs at crossovers, create
much highe
r vibration forces than typical track conditions. Because
of
the higher vibration levels at special trackwork, crossovers are the
principal areas of vibration impact on new systems. Methods of
mit
igating the vibration impact include modifying the track s
upport
s
ystem, installing low-impact frogs, or relocating the crossover. Specia
l
t
rack support systems such as ballast mats, high-resilience trac
k
fa
steners, resiliently supported ties, and floating slabs have all
been
s
hown to be effective in reducing vibration levels
.
T
he condition of the running surface of the rails can strongly affec
t
v
ibration levels. Factors such as corrugations, general wear, or mill sca
le
on
new track can cause vibration levels 5 to 15 dB higher than norma
l.
Mill
scale will typically wear away after some time in service, but t
he
track must be ground to remove corrugations or to reduce the
r
oughness from wear
.
R
oadway surfaces in the rubber-tired vehicle base curve are assumed t
o
be
smooth. Rough washboard surfaces, bumps, or uneven expans
ion
joint
s are the types of running surface defects that cause increas
ed
v
ibration levels over the smooth road conditi
on.
T
he adjustments in this category are not additive; apply the greate
st
a
pplicable value only. If there are adjustments for vehicle parameter
s
and the track is worn or corrugated, only include one adjustment.
2b
. Apply path adjustments to the base curve using Table 6-12 and the
descriptions below to account for the project-specific path characteristics.
FEDERAL TRANSIT ADMINISTRATION 142
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Table 6-12 Path Adjustment Factors for Generalized Predictions of GB Vibration and Noise
Path Factor
Adjustment to Propagation Curve
Comment
Resiliently
Supported
Ties
(Low-
Vibration
Track, LVT)
-10 dB
Resiliently supported tie systems have been
found to provide very effective control of
low-frequency vibration.
Track Structure (not additive, apply greatest value only)
Type of
Transit
Structure
Relative to at-grade tie & ballast:
Elevated structure
-10 dB
Open cut
0 dB
In general, the heavier the structure, the
lower the vibration levels. Putting the track
in cut may reduce the vibration levels slightly.
Rock-based subways generate higher-
frequency vibration.
Relative to bored subway tunnel in soil:
Station
-5 dB
Cut and cover
-3 dB
Rock-based
-15 dB
Ground-borne Propagation Effects
Geologic
conditions that
promote
efficient
vibration
propagation
Efficient propagation in soil
+10 dB
Refer to the text for guidance on identifying
areas where efficient propagation is possible.
Propagation
in rock layer
Dist.
50 ft
100 ft
150 ft
200 ft
Adjust.
+2 dB
+4 dB
+6 dB
+9 dB
The positive adjustment accounts for the
lower attenuation of vibration in rock
compared to soil. It is generally more difficult
to excite vibrations in rock than in soil at the
source.
Coupling to
building
foundation
Wood-Frame Houses
1-2 Story Masonry
3-4 Story Masonry
Large Masonry on Piles
Large Masonry on Spread
Footings
Foundation in Rock
-5 dB
-7 dB
-10 dB
-10 dB
-13 dB
0 dB
In general, the heavier the building
construction, the greater the coupling loss.
In addition to the comments in Table 6-12, use the following guidelines to
select the appropriate adjustment factors.
Track Structure – The weight and size of a transit structure affect
s
the vibration radiated by that structure. In general, vibration levels are
lower
for heavier transit structures. Therefore, the vibration levels fr
om
a
cut-and-cover concrete double-box subway can be assumed to
be
lower
than the vibration from a lightweight concrete-lined bored t
unnel.
T
he vibration from elevated structures is lower than from at-grade
track because of the mass and damping of the structure and the extra
distance that the vibration must travel before it reaches the receiver.
Elevated structures in AGT applications are sometimes designed to bear
on building elements. This is a special case and may require detailed
design considerations.
The adjustments in this category are not additive; apply the greatest
applicable value only.
FEDERAL TRANSIT ADMINISTRATION 143
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Ground-Borne Propagation Effects – Geologic Conditions –
Although it is known that geologic conditions have a considerable effect
on
the vibration levels, it is rarely possible to develop more than
a
g
eneral understanding of the vibration propagation characteristics
for a
Gener
al Vibration Assessment. One of the challenges with identify
ing
t
he cause of efficient propagation is the difficulty in determining whet
her
hig
her than normal vibration levels are due to geologic conditions
or
due
to special source conditions (e.g., rail corrugations or wheel flats)
.
Some
geologic conditions are repeatedly associated with efficient
propagation. Shallow bedrock, less than 30 ft below the surface, is likely
to have efficient propagation. Soil type and stiffness are also important
factors in determining propagation characteristics. In particular, stiff,
clayey soils, consolidated sand, gravel, and glacial till can be associated
with efficient vibration propagation. Investigation of soil boring records
can be used to estimate depth to bedrock and the presence of problem
soil conditions.
A conservative approach would be to use the 10-dB adjustment for
efficient propagation for areas where efficient propagation is likely.
However, this adjustment can greatly overstate the potential for
vibration impact where efficient propagation is not present and should
be applied using good judgment. Review available geological data and any
complaint history from existing transit lines and major construction
sites near the transit corridor to identify areas where efficient
propagation is possible. If there is reason to suspect efficient
propagation conditions, conduct a Detailed Vibration Analysis during the
engineering phase and include vibration propagation tests at the areas
with potential for efficient propagation.
Track Structure and Geologic Conditions – Exampl
es
S
ubw
ay
For
a subway, determine if the subway will be founded in bedr
ock.
Bedroc
k is considered to be hard rock. It is usually appropriate t
o
c
onsider soft siltstone and sandstone to be more like soil than har
d
r
ock. Whether a subway is founded in soil or rock can make a 15-
dB difference in the vibration levels.
When a subway structure is founded in rock, include the following
Track Structure and Ground-borne Propagation Effects adjustments
from Table 6-12:
- Type of Transit Structure adjustment: Rock-based – 15 dB
- Geologic Conditions adjustment: Propagation in rock layer
for the appropriate distance.
This adjustment increases with distance because vibration
attenuates more slowly in rock than in the soil used as a basis for
the reference curve.
At-grade – When considering at-grade vibration sources, determine
if
the vibration propagation characteristics are typical or efficient. Efficient
FEDERAL TRANSIT ADMINISTRATION 144
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
vibration propagation results in vibration levels approximately 10 dB
higher than typical levels. This more than doubles the potential impact
zone for ground-borne vibration.
Ground-Borne Propagation Effects – Coupling to Buildin
g
F
oundation – Since annoyance from ground-borne vibration and nois
e
is
an indoor phenomenon, the effects of the building structure on t
he
v
ibration must be considered. Wood-frame buildings, such as typica
l
r
esidential structures, are more easily excited by ground vibration tha
n
hea
vier buildings. In contrast, large masonry buildings with sprea
d
footings have a low response to ground vibration.
When a building foundation is directly on the rock layer, there is no
coupling loss due to the weight and stiffness of the building. Use the
standard coupling factors based on building type if there is at least a 10-
foot layer of soil between the building foundation and the rock layer.
2c. Apply receiver adjustments to the base curve using Table 6-13 and the
descriptions below to account for the project-specific receiver characteristics.
The data in Table 6-13 is applicable when the building structural features are
known.
For more generic cases that do not have detailed information on individual
buildings, use a conservative approach and apply the following adjustments to
predict indoor vibration based on the outdoor vibration, instead of using the
adjustments in Table 6-13:
(43)(
50
)
Light-weight, wood-frame construction 1st floor: +3 dB
Lig
ht-weight, wood-frame construction 2nd and 3rd floors: +6 d
B
Large buildings: 0 dB
Sma
ll masonry buildings: +3
dB
Table 6-13 Receiver Adjustment Factors for Generalized Predictions of GB Vibration and Noise
Receiver
Factor
Adjustment to
Propagation Curve
Comment
Floor-to-floor
attenuation
1 to 5 floors
above grade
5 to 10 floors
above grade
-2 dB/floor
-1 dB/floor
This factor accounts for dispersion and attenuation
of the vibration energy as it propagates through a
building starting with the first suspended floor.
*
Amplification
due to
resonances of
floors, walls,
and ceilings
+6 dB
The actual amplification will vary greatly depending
on the type of construction. The amplification is
lower near the wall/floor and wall/ceiling
intersections.
* Floor-to-floor attenuation adjustments for the first floor assume a basement.
FEDERAL TRANSIT ADMINISTRATION 145
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
In addition to the comments in Table 6-13, use the following guidelines to select
the appropriate adjustment factors. Note that receiver adjustments are additive.
Vibration generally reduces in level as it propagates through a building.
As indicated in Table 6-13, a 1- to 2-decibel attenuation per floor is
typically appropriate.
Resonances of the building structure, particularly the floors, will cause
some amplification of the vibration. Consequently, for a wood-frame
structure, the building-related adjustments nearly cancel out. Example:
All adjustments for the first floor assuming a basement are: -5 dB for
the coupling loss; -2 dB for the propagation from the basement to the
first floor; and +6 dB for the floor amplification. The total adjustment in
this case is -1 dB.
2d. Apply adjustments to the final adjusted curve using Table 6-14 and the
descriptions below to convert ground-borne vibration levels to ground-borne
noise levels.
Table 6-14 Conversion to Ground-borne Noise
Conversion to Ground-borne Noise
Noise Level in
dBA
Peak frequency of ground vibration:
Low frequency (<30 Hz)
-50 dB
Mid Frequency (peak 30 to
-35 dB
60 Hz)
High frequency (>60 Hz)
-20 dB
Use these adjustments to estimate the A-
weighted sound level given the average
vibration velocity level of the room surfaces.
See text for guidelines for selecting low-,
mid-, or high-frequency characteristics. Use
the high-frequency adjustment for subway
tunnels in rock or if the dominant
frequencies of the vibration spectrum are
known to be 60 Hz or greater.
Estimate the levels of radiated noise using the average vibration amplitude of the
room surfaces (floors, walls, and ceiling), and the total acoustical absorption in
the room.
The un-weighted sound pressure level is approximately 5 dB
(37)(43)
less than the
vibration velocity level when the velocity level is referenced to 1x10
-6
inches/sec; but for a better estimate, it is necessary to consider general
frequency ranges. Since ground-borne noise is A-weighted, the adjustments vary
by frequency range, as described below. See Appendix B.1.4.1 for more
information on A-weighting.
To select the appropriate adjustment, classify the frequency characteristics
according to the guidelines below.
FEDERAL TRANSIT ADMINISTRATION 146
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Low Frequency (<30 Hz) – Low-frequency vibration characteristics
can be assumed for the following conditions:
Subways surrounded by cohesionless sandy soil
Vibration isolation track support systems
Most surface track
Mid Frequency (peak 30 to 60 Hz) – The mid-frequency vibration
characteristic can be assumed for the following conditions:
Subways, unless other information indicates that one of the other
assumptions is appropriate,
Surface track when the soil is very stiff with high clay content
High Frequency (>60 Hz) – High-frequency characteristics can be
assumed for the following conditions:
Subways with the transit structure founded in rock
Subways, when there is very stiff, clayey soil
Step 3: Inventory of Vibration Impact
Take inventory of vibration-sensitive land uses with impact and determine if a Detailed
Vibration Analysis is required.
Compare the projected vibration levels, including all appropriate adjustments in
Section 6.4, Step 2, to the criteria to determine if impact from ground-borne
vibration or noise is likely. Note that for any transit mode, variation in vibration
levels under apparently similar conditions is not uncommon. In the General
Vibration Assessment, it is preferable to make a conservative assessment of the
impact and include buildings that may ultimately not be subject to impact.
The standard curves in Section 6.4, Step 1, represent the upper range of
vibration levels from well-maintained systems. Although actual levels fluctuate
widely, it is rare that ground-borne vibration will exceed these curves by more
than 1 or 2 dB unless there are extenuating circumstances such as wheel- or
running-surface defects. However, because actual levels of ground-borne
vibration will sometimes differ substantially from the projections, use the
following guidelines to interpret vibration impact:
Projected vibration is below the impact threshold – Vibration impact
is unlikely, and the environmental document should state this.
Projected ground-borne vibration is 0 to 5 dB greater than the
impact threshold – There is a strong chance that actual ground-borne
vibration levels will be below the impact threshold. The environmental
document should report impact at these locations as exceeding the
applicable threshold, present possible mitigation measures and costs, and
commit to conducting more detailed studies to refine the vibration impact
analysis during the engineering phase. During the Detailed Vibration
Analysis, determine appropriate mitigation, if necessary. A site-specific
Detailed Vibration Analysis may show that vibration impacts will not occur
and control measures are not needed.
FEDERAL TRANSIT ADMINISTRATION 147
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Projected ground-borne vibration is 5 dB or greater than the
impact threshold – Vibration impact is probable and Detailed Vibration
Analysis must be conducted during the engineering phase to determine
appropriate vibration control measures. The environmental document
should report impact at these locations as exceeding the applicable
threshold, present possible mitigation measures and costs, and commit to
conducting more detailed studies to refine the vibration impact analysis
during the engineering phase. During the Detailed Vibration Analysis,
determine appropriate mitigation, if necessary. A site-specific, Detailed
Vibration Analysis may show that very costly vibration mitigation must be
incorporated into the project to eliminate the impacts.
FTA recommends the reporting of a vibration level as a single value and not as a
range, as ranges tend to confuse the interpretation of impact.
Express the results of the General Vibration Assessment in terms of an
inventory with the following components:
Include all vibration-sensitive land uses as identified in the Vibration
Screening Procedure.
Organize the inventory according to the categories described in Table
6-8.
Include information on potentially feasible mitigation measures to
reduce vibration to acceptable levels based on the generalized reduction
estimates provided in this section. To be considered feasible, the
measure or combination of measures must provide at least a 5-dB
reduction of the vibration levels and be reasonable in terms of cost.
These potential mitigation measures are considered preliminary. Final vibration
mitigation measures can only be specified after a Detailed Vibration Analysis has
been done; see Section 6.5 for more information. Vibration control is
frequency-dependent; therefore, specific recommendations of vibration control
measures can only be made after evaluating the frequency characteristics of the
vibration.
Example 6-1 General Vibration Assessment – LRT
General Vibration Assessment for an LRT project
The hypothetical project is a LRT system that operates at 40 mph on at-grade, ballast and tie track with welded
rail. The first floor of houses is at 125 ft from the LRT tracks and there is efficient propagation through the soil.
The houses are constructed with wood frames. The houses will be exposed to 260 train passbys per day.
Calculate the ground-borne vibration and assess for impact.
Select Base Curve for Ground Surface Vibration
Determine the appropriate base curve and the RMS velocity level (
.
According to Table 6-9, the Rapid Transit or Light Rail Vehicles curve is appropriate.
at 125 ft for this curve at 50 mph
Apply Adjustments
Apply the appropriate source adjustments using Table 6-11.
FEDERAL TRANSIT ADMINISTRATION 148
Apply the appropriate path adjustments using Table 6-12.
Apply the appropriate receiver adjustments using Table 6-13.
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Assess for Impact
Because there are more than 70 events per day, this project is in the Frequent Events category (Table 6-2). For
category 2 land uses (residences) with frequent events, the impact criteria is 72 VdB (Table 6-3). Therefore,
according to the General Vibration Assessment, there is potential for impact and a Detailed Vibration Analysis
should be completed.
6.5 Evaluate Impact: Detailed Vibration Analysis
Evaluate for impact using the Detailed Vibration Analysis procedure, if appropriate
(Section 6.1).
The goal of the Detailed Vibration Analysis is to use all available tools to
develop accurate projections of potential ground-borne vibration impact and
when necessary, to design mitigation measures. A Detailed Vibration Analysis
requires developing estimates of the frequency components of the vibration
signal, usually in terms of 1/3-octave-band spectra. The analytical techniques for
solving vibration problems are complex, and the technology continually
advances. Therefore, the approach presented in this section focuses on the key
steps for these analyses. The key elements of the Detailed Vibration Analysis
procedure and recommended steps are described below.
The methods in this section generally assume a steel-wheel/rail system. The
procedures could be adapted to bus systems. However, this is rarely necessary
because vibration impact is very infrequent with rubber-tired transit.
In general, when situations arise that are not explicitly covered in the Detailed
Vibration Analysis, professional judgment may be used to extend these methods
to cover these unique cases, when appropriate. Appendix G provides
information on developing and using non-standard modeling procedures.
Step 1: Characterize Existing Vibration Conditions
Conduct measurements to survey and document the existing vibration conditions.
In contrast to noise impact analysis, the existing ambient vibration is not
required to assess vibration impact in most cases; but, it is important to
FEDERAL TRANSIT ADMINISTRATION 149
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
document general background vibration in the project corridor. Because the
existing environmental vibration is usually below human perception, a limited
vibration survey is sufficient even for a Detailed Vibration Analysis.
It is particularly valuable to survey vibration conditions at sensitive locations for
the following reasons:
To obtain valuable information on the true sensitivity of the activity to
external vibration and obtain a reference condition under which
vibration is not problematic.
To document that existing vibration levels are above or below the
normal threshold of human perception for the existing condition.
To document levels of vibration created by existing rail lines. If vibration
from an existing rail line is higher than the proposed train, there may
not be impact even if the standard impact criteria are exceeded.
To use existing vibration sources to characterize propagation. Existing
vibration sources such as freight trains, industrial processes, quarrying
operations, or normal traffic can be used to characterize vibration
propagation. Carefully designed and performed measurements may
eliminate the need for more complex propagation tests. See Appendix
G for information on using non-standard modeling procedures.
To identify the potential for efficient vibration propagation. If a
measurement site has existing vibration approaching the range of human
perception (e.g., the maximum vibration velocity levels are greater than
about 65 VdB), then this site should be carefully evaluated for the
possibility of efficient vibration propagation.
Conduct measurements to characterize existing vibration conditions. The goal
of most ambient vibration measurements is to characterize the rms vertical
vibration velocity level at the ground surface. In almost all cases, it is sufficient to
measure only vertical vibration and ignore the transverse components of the
vibration. Although transverse components
(
51
)
can transmit vibration energy into
a building, the vertical component typically dominates.
1a. Choose Measurement Locations – Conduct outdoor and/or indoor
measurements to characterize existing vibration conditions, as appropriate,
for the project. Although ground-borne vibration is almost exclusively a
problem inside buildings, it is generally recommended to perform
measurements outdoors because equipment inside the building may cause
more vibration than exterior sources. Additionally, the building structure
and the resonances of the building can have strong effects on the vibration
that are difficult to predict. It can also be important to measure and
document those indoor sources of vibration. These indoor sources may
cause vibration greater than that due to external sources like street traffic
or aircraft overflights. When measuring (indoor) floor vibration, take
measurements near the center of a floor span where the vibration
amplitudes are the highest.
FEDERAL TRANSIT ADMINISTRATION 150
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
1b. Measurement Considerations
Site selection – Selecting sites for an ambient vibration survey
r
equires good judgment. Sites selected to characterize a transit corr
idor
s
hould be distributed along the entire project where potential
for
impa
cts have been identified and should be representative of the ty
pes
of
vibration environments found in the corridor. This would comm
only
include:
Meas
urements in quiet, residential areas removed from major tra
ffic
a
rterials to characterize low-ambient vibration areas
;
Meas
urements along major traffic arterials and highways or freeway
s
to characterize high-ambient vibration areas;
Meas
urements in any area with vibration-sensitive activities; a
nd
Measurements at any major existing source of vibration such as
r
ailroad lines
.
Transducer placement – Place the transducers near the building
s
etback line. For ambient measurements along railroad lines, it
is
r
ecommended to inc
lude:
Mult
iple sites at several distances from the rail line at each site, a
nd
4
to 10 train passbys for each test
.
Beca
use of the irregular schedule for freight trains and the low number
of operations each day, it is often impractical to perform tests at more
than two or three sites along the rail line or to measure more than two
or three passbys at each site.
Rail type and condition strongly affect the vibration levels.
Consequently, it is important to inspect the track to locate any
switches, bad rail joints, corrugations, or other factors that could be
responsible for higher than normal vibration levels. Locations with these
kinds of irregularities should be represented in addition to locations
with rail in better condition.
Transducer mounting methods – The way a transducer is mounte
d
c
an affect the measured levels of ground-borne vibrati
on.
Stra
ightforward methods of mounting transducers on the grou
nd
surface or on pavement are adequate for vertical vibration
mea
surements for the frequencies of concern for ground-bor
ne
vibration (less than about 200 Hz).
Q
uick-drying epoxy, clay, or beeswax can be used to moun
t
t
ransducers to smooth paved surfaces or metal stakes driven int
o
t
he grou
nd.
R
ough concrete or rock surfaces require special mountings. On
e
a
pproach is to use a liberal base of epoxy to attach small a
luminum
block
s to the surface, and then mount the transducers on t
he
a
luminum blocks
.
When
in doubt, review the specific transducer documentation a
nd
dis
cuss additional mounting guidance with the transduc
er
manufa
cturer
.
FEDERAL TRANSIT ADMINISTRATION 151
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
1c. Existing Vibration Characterization – The appropriate methods of
characterizing ambient vibration are dependent on the type of information
required for the analysis. Consider the following when characterizing the
existing vibration:
Ambient vibration – Ambient vibration is usually characterized with a
continuous 10- to 30-minute measurement of vibration. The rms
velocity level of the vibration velocity level over the measurement
period provides an indication of the average vibration energy. The rms
velocity level over the measurement period is typically equivalent to a
long averaging time rms level.
Specific events – Characterize specific events such as train passbys by
the rms level over the time that the train passes by. If the locomotives
produce vibration levels more than 5 dB higher than the passenger or
freight cars, obtain a separate rms level for the locomotives. The
locomotives can usually be characterized by the L
max
during the train
passby. The rms averaging time or time constant should be 1 second
when determining L
max
. In some cases, it may be adequate to
characterize the train passby using L
max
, which is simpler to obtain than
the rms averaged over the entire train passby.
Spectral analysis – Perform a spectral analysis of vibration
propagation data. For example, if vibration transmission of the ground is
suspected of having particular frequency characteristics, use 1/3-octave
band charts to describe vibration behavior. Narrowband spectra also
can be valuable, particularly for identifying discrete frequency
components and designing specific mitigation measures.
Note that it is preferred to characterize existing vibration in terms of
the rms velocity level instead of the peak PPV, which is commonly used
to monitor construction vibration. As discussed in Section 5.1, rms
velocity is considered more appropriate than PPV for describing human
response to building vibration.
Step 2: Estimate Vibration Impact
Estimate ground-borne vibration and noise at sites where significant impact is probable
and assess for impact.
Predicting ground-borne vibration associated with a transportation project
continues to be a developing field. Because ground-borne vibration is a complex
phenomenon that is difficult to model and predict accurately, most projection
procedures that have been used for transit projects rely on empirical data.
The procedure described in this section is based on site-specific tests of
vibration propagation. This procedure was developed under a FTA-funded
research contract
(
52
)
and is recommended for detailed evaluations of ground-
borne vibration. Other approaches to a prediction procedure, such as finite
element methods, can be used. See Appendix G for information on using non-
standard modeling procedures.
FEDERAL TRANSIT ADMINISTRATION 152
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Overview of Prediction Procedure – This procedure was developed to
allow the use of data collected in one location to accurately predict vibration
levels in another site where the geologic conditions may be completely different.
The procedure is based on transfer mobility. Transfer mobility is the complex
velocity response produced by a point force as a function of frequency. It
represents the relationship between a vibration source that excites the ground
and the resulting vibration of the ground surface. It is a function of both
frequency and distance from the source. The analyses in this manual focus on
transfer mobility magnitude, which is the magnitude for the velocity relative to
the force without reference to phase. The transfer mobility level is the level in
decibels relative to 1E-6 in/lb-s.
The transfer mobility measured at an existing transit system is used to
normalize ground-borne vibration data and remove the effects of geology. The
normalized vibration is referred to as the force density. Force density is the
force per root distance along the track in lb/ft
1/2
. The force density can be
combined with transfer mobility measurements at vibration-sensitive sites along
a new project to develop projections of future ground-borne vibration.
The transfer mobility between two points completely defines the composite
vibration propagation characteristics between the two points. In most practical
cases, receivers are close enough to the train tracks that the vibration cannot
be considered as originating from a single point. Therefore, the vibration source
must be modeled as a line-source. Consequently, the point transfer mobility
must be modified to account for a line-source. The subsequent line-source
transfer mobility is given in units of decibels relative to 1e-6 in/s/lb/sqrt(ft).
The prediction procedure considers ground-borne vibration to be divided into
several basic components described below and shown in Figure 6-5.
Excitation Force (Force Density) – The vibration energy is creat
ed
by
oscillatory and impulsive forces. Steel wheels rolling on smooth st
eel
r
ails create random oscillatory forces. When a wheel encounters
a
dis
continuity such as a rail joint, an impulsive force is created. The forc
e
exc
ites the transit structure, such as the subway tunnel or the ballas
t
for at
-grade trac
k.
In
the prediction method, the combination of the actual force generated
at the wheel/rail interface and the vibration of the transit structure are
usually combined into an equivalent force density level. The force
density level is the level in decibels of the force density relative to 1
lb/ft
1/2
and describes the force that excites the soil/rock surrounding the
transit structure.
Vibration Propagation (Transfer Mobility) – The vibration of t
he
t
ransit structure causes vibration waves in the soil that propagate awa
y
fr
om the transit structure. The vibration energy can propagate thr
ough
t
he soil or rock in a variety of wave forms. All ground vibration inc
ludes
s
hear and compression waves. Rayleigh waves
(49)
are also created and
pr
opagate along the ground surface. These Rayleigh waves can be
a
FEDERAL TRANSIT ADMINISTRATION 153
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
major carrier of vibration energy. The mathematical modeling of
vibration is complicated when there are soil strata with different elastic
properties, which is common. As indicated in Figure 6-5, the
propagation through the soil/rock is modeled using the transfer
mobility, which is usually determined experimentally.
The combination of the force density level and the transfer mobility is
used to predict the ground- surface vibration. This is the major
difference from the General Vibration Assessment, which generalizes
estimates of the ground-borne vibration.
Building Vibration – When the ground vibration excites a buil
ding
foundation, it sets the building into vibratory motion and vibration
wa
ves propagate throughout the building structure. The interacti
on
between the ground and the foundation causes some reduction in
vibration levels. The amount of reduction is dependent on the mass and
s
tiffness of the foundation. The more massive the foundation, the lowe
r
t
he response to ground vibration. As the vibration waves propagat
e
t
hrough the building, they can create vibration that can be felt and caus
e
wi
ndows and household items to rattl
e.
Au
dible Noise – In addition to vibration that can be felt, the vibratio
n
of
room surfaces radiates low-frequency sound that may be audible. T
he
s
ound level is affected by the amount of acoustical absorption in t
he
r
eceiver roo
m.
Figure 6-5 Ground-Borne Vibration and Noise Model
A fundamental assumption of the prediction approach outlined in this section is
that the force density, transfer mobility, and the building coupling to the ground
are all independent factors. The following equations are the basis for the
FEDERAL TRANSIT ADMINISTRATION 154
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
prediction procedure, where all of the quantities are one-third octave band
spectral levels in decibels with consistent reference values:
Eq. 6-5
where:
Eq. 6-6
= rms vibration velocity level in VdB
= force density level in dB for a line vibration source such as a
train
= line-source transfer mobility level in dB from the tracks to the
sensitive site
= adjustments to account for ground-building foundation
interaction and attenuation of vibration amplitudes as vibration
propagates through buildings
= A-weighted sound level
= adjustment to account for conversion from vibration to sound
pressure level including accounting for the amount of acoustical
absorption inside the room. A value of -5 dB can be used for K
rad
for typical residential rooms when the decibel reference value
for L
v
is 1 micro in/sec
(37)(50)
= A-weighting adjustment at the 1/3-octave band center frequency
All of the quantities given above are functions of frequency, and the standard
approach is to develop projections on a 1/3-octave band basis using the average
values for each 1/3-octave band. The end results of the analysis are the 1/3-
octave band spectra of the ground-borne vibration and the ground-borne noise.
The spectra are then compared to the vibration criteria for the Detailed
Vibration Analysis. The A-weighted ground-borne noise level can be calculated
from the vibration spectrum and compared to the criteria. This more detailed
approach differs from the General Vibration Assessment, where the overall
vibration velocity level and A-weighted sound level are predicted without any
consideration of the particular frequency characteristics of the propagation path.
The key steps in obtaining quantities for Eq. 6-5 and Eq. 6-6 are presented in the
following steps and include:
Step 2a. Estimate force density
Step 2b. Measure the point-source transfer mobility
Step 2c. Estimate line-source transfer mobility
Step 2d. Project ground-borne vibration and ground-borne noise
2a. Estimate Force Density – The estimate of force density can be based on
previous measurements or a special test program can be designed to measure
the force density at an existing facility.
If no suitable measurements are available, conduct testing at a transit facility
with equipment similar to the planned vehicles. Adjustments for factors such as
train speed, track support system, and vehicle suspension may be needed to
match the force density to the conditions at a specific site. Review the report
FEDERAL TRANSIT ADMINISTRATION 155
where:
= force density level in dB
= measured train ground-borne vibration
level in VdB
= line-source transfer mobility level in dB
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
"State-of- the-Art Review: Prediction and Control of Ground-Borne Noise and
Vibration from Rail Transit Trains"
(41)
for examples of appropriate adjustments.
Force density is not a quantity that can be measured directly; it must be inferred
from measurements of transfer mobility and train vibration at the same site. To
derive force density, the best results are achieved by deriving line-source
transfer mobility from a line of impacts. The standard approach is to average the
force density from measurements at three or more positions at one site. If
feasible, it is recommended to take measurements at more than one site and at
multiple speeds.
If no suitable measurements are available, see Steps 2b and 2c for guidelines on
obtaining line-source transfer mobility.
The force density for each 1/3-octave band is as follows:
Eq. 6-7
Figure 6-6 shows example trackbed force densities in decibels relative to 1
lb/(ft)
1/2
. These force densities were developed from measurements of vibration
from heavy and LRT vehicles and represent an incoherent line of vibration force
equal to the length of transit trains. This figure provides a comparison of the
vibration forces from heavy commuter trains and LRT vehicles with different
types of primary suspensions, illustrating the range of vibration forces commonly
experienced in a transit system. A force density of a vehicle includes the
characteristics of its track support system at the measurement site. Adjustments
must be applied to the force density to account for differences between the
facility where the force density was measured and the new system being
analyzed.
Figure 6-7 shows typical force densities for rail transit vehicles at 40 mph on
ballast and tie tracks, which are approximately within the tolerances shown in
Figure 6-6. The force densities should be applied very carefully for other track
types and speeds. The embedded tracks, although considerably stiffer than
ballast and tie tracks, are expected to show similar force density levels.
(
53
)
The
curves in Figure 6-7 should also be applied with caution for newer generations
of light rail vehicles as well as vehicles that utilize direct fixation tracks. The
preferred approach for vibration predictions would be to perform force density
measurements at a system with vehicles and operations that are similar to those
of the future project.
FEDERAL TRANSIT ADMINISTRATION 156
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Figure 6-6 Typical Force Densities for Rail Transit Vehicles, 40 mph
Figure 6-7 Typical Force Densities for LRT Vehicles, 40 mph
2b. Measure Point-Source Transfer Mobility – Using the appropriate
instrumentation, measure point-source transfer mobility for sources with short
lengths, such as buses or single car vehicles or columns supporting elevated
structures. For longer vehicles, see Section 2c for a discussion of measuring line-
source transfer mobilities.
The test procedure to measure point-source transfer mobility consists of
impacting the ground by dropping a heavy weight and measuring the force into
the ground and the response at several distances from the impact. Other
excitation sources may include swept sine, sine-dwell, random vibration, and
maximum length sequence. The goal of the test is to create vibration pulses that
FEDERAL TRANSIT ADMINISTRATION 157
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
travel from the source to the receiver using the same path that will be taken by
the transit system vibration.
Figure 6-8 illustrates the field procedure for measuring both at-grade and
subway testing of transfer mobility. A weight is dropped from a height of 3 to 4
ft onto a force transducer. The responses of the force and vibration transducers
are recorded on a multichannel recorder for later analysis in the laboratory. An
alternative approach is to set up the analysis equipment in the field and capture
the signals directly. This complicates the field testing, but eliminates the
laboratory analysis of recorded data.
Figure 6-8 Test Configuration for Measuring Transfer Mobility
When the procedure is applied to subways, the force must be located at the
approximate depth of the subway. This is done by drilling a bore hole and
locating the force transducer at the bottom of the hole. The tests are usually
performed while the bore holes are drilled to allow for the use of the soil-
sampling equipment on the drill rig for the transfer mobility testing. The force
transducer is attached to the bottom of the drill string and lowered to the
bottom of the hole. A standard soil sampling hammer is used to excite the
ground; typically, a 140-pound weight is dropped 18 inches onto a collar that is
attached to the drill string. The force transducer must be capable of operating
under water if the water table is near the surface or a slurry drilling process is
used.
Standard signal-processing techniques are used to determine the transfer
function (frequency response function) between the exciting force and the
resultant ground-borne vibration. Numerical regression methods are used to
combine a number of two-point transfer functions into a smooth point-source
transfer mobility level that represents the average vibration propagation
characteristics of a site as a function of both distance from the source and
FEDERAL TRANSIT ADMINISTRATION 158
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
frequency. The transfer mobility level is usually expressed in terms of a group of
1/3-octave band transfer mobility levels. Figure 6-9 is an example of point-
source transfer mobility levels from a series of tests at the Transportation
Technology Center in Pueblo, Colorado.
(50)(
54
)(
55
)(
56
)(
57
)
Figure 6-9 Example of Point-Source Transfer Mobility
₋
Instrumentation
Performing a transfer mobility test requires specialized equipment, which is
generally available from commercial sources. Typical instrumentation for field-
testing and laboratory analysis of transfer mobility is shown in Figure 6-10.
A load cell can be used as the force transducer. The force transducer should be
capable of impact loads of 5,000 to 50,000 pounds depending on the hammer
used for the impact. For borehole testing, the load cell must be hermetically
sealed and capable of being used at the bottom of a 30- to 100-foot-deep hole
partially filled with water.
Either accelerometers or geophones can be used as the vibration transducers.
Geophones should be carefully mounted so that they are vertical. The
requirement is that the transducers with the associated amplifiers be capable of
accurately measuring levels of 0.0001 in/sec at 40 Hz and have a flat frequency
response from 6 Hz to 400 Hz. Data should be acquired with a digital
acquisition system with a flat frequency response over the range of 6 to 400 Hz.
FEDERAL TRANSIT ADMINISTRATION 159
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Figure 6-10 Equipment Required for Field Testing and Laboratory Analysis
A narrowband spectrum analyzer or signal-processing software can be used to
calculate the transfer function and coherence between the force and vibration
data. The analyzer must be capable of capturing impulses from at least two
channels to calculate the frequency spectrum of the transfer function between
the force and vibration channels. All transfer functions should include the
average of at least 20 impulses. Time averaging of the impulses will provide
substantial signal enhancement, which is usually required to accurately
characterize the transfer function. Signal enhancement is particularly important
when the vibration transducer is more than 100 ft from the impact.
Alternative methods of determining transfer mobility may be used, provided
that these techniques have been demonstrated to provide the same results as
the conventional weight-drop method over the frequency range of 6 Hz to 400
Hz. See Appendix G for information on developing and using non-standard
procedures. These methods may include using other impulse-response
measurement systems involving the use of shakers or electro-mechanical
actuators, stimuli such as sweeps or maximum length sequences (MLS), and
various signal processing techniques. A forthcoming ANSI Standard will describe
in detail the procedures, methodologies, and reporting requirements for
performing ground-borne vibration propagation measurements.
The transfer function can be calculated with either a spectrum analyzer or
signal-processing software. Note that transfer functions should include the
average of at least 20 impulses. Specialized multi-channel spectrum analyzers
have built-in capabilities for computing transfer functions and are
computationally efficient. However, signal-processing software can offer more
FEDERAL TRANSIT ADMINISTRATION 160
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
flexibility in analyzing data signals and allows the use of different digital signal
processing methods. Typical measurement programs involve acquisition of data
in the field and later processing of the information in a laboratory. However,
recent advances in instrumentation and signal-processing software allow data to
be collected and analyzed while in the field.
2c. Estimate Line-Source Transfer Mobility – Estimate line-source
transfer mobility for long sources such as multi-car trains. Line-source transfer
mobilities are used to normalize measured vibration velocity levels from train
passbys and to obtain force density. Two different approaches can be used to
develop estimates of line-source transfer mobility. The first consists of using
lines of transducers and the second consists of a line of impact positions.
Option A: Lines of Transducers – Develop line-source transfer mobility
curves from tests using one or more lines of transducers as shown in Figure
6-11 and described below.
Figure 6-11 Analysis of Transfer Mobility
Ai. Obtain the narrowband transfer function between source and receiver at
each measurement position. There should be a minimum of four distances in any
test line. Because of the possibility of local variations in propagation
characteristics, two or more lines should be used to characterize a site if
possible. A total of 10 to 20 transducer positions are often used to characterize
a site.
Aii. Calculate the equivalent 1/3-octave band transfer functions, generally
between 6 and 400 Hz. This reduces each spectrum to 15 numbers. As shown
in Figure 6-11, the 1/3-octave band spectrum is much smoother than the
narrowband spectrum.
Aiii. Calculate a best-fit curve of transfer mobility as a function of distance for
each 1/3-octave band. When analyzing a specific site, the best-fit curve will be
FEDERAL TRANSIT ADMINISTRATION 161
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
based on 10 to 20 points. Up to several hundred points could be used to
determine average best-fit curves for a number of sites.
Aiv. Apply the best-fit curve to the vibration sources. The 1/3-octave band
best-fit curves can be directly applied to point vibration sources. Buses can
usually be considered point-sources, as can columns supporting elevated
structures. However, for a line vibration source such as a train, numerical
integration must be used to calculate the equivalent line-source transfer
mobility. The numerical integration procedures are detailed in the TRB
publication: “A Prediction Procedure for Rail Transportation Ground-Borne
Noise and Vibration.”
(50)
Option B: Line of Impulses – This second procedure for estimating line-
source transfer mobility is best for detailed assessment of specific vibration
paths or specific buildings and is a more direct approach.
Bi. Measure multiple point-source transfer mobilities according to the
procedures in Step 2b above. The vibration transducers are placed at specific
points of interest and a line of impacts is used. For example, a 150-foot train
might be represented by a line of 11 impact positions along the track centerline
at 15-foot intervals (Figure 6-12).
Bii. Sum the point-source results using Simpson's rule
xiii
for numerical
integration to calculate the line-source transfer mobility.
Figure 6-13 shows an example of line-source transfer mobilities that were
derived from the point-source transfer mobilities shown in Figure 6-9.
Figure 6-12 Schematic of Transfer Mobility Measurements Using a Line of Impacts
xiii
Simpson’s rule is a method for approximating integrals.
FEDERAL TRANSIT ADMINISTRATION 162
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Figure 6-13 Example of Line-source Transfer Mobility
₋
2d. Project Ground-Borne Vibration and Noise – Combine force density
and line-source transfer mobility to project ground-borne vibration. Then, apply
adjustment factors to estimate the building response to the ground-borne
vibration and to estimate the A-weighted sound level inside buildings.
The propagation of vibration from the building foundation to the receiver room
is very complex and dependent on the specific design of the building. Detailed
evaluation of the vibration propagation would require extensive use of
numerical procedures such as the finite element method. Such a detailed
evaluation is generally not practical for individual buildings considered in this
manual. If the detailed features of the individual buildings are available, the
recommended procedure is to estimate the propagation of vibration through a
building and the radiation of sound by vibrating building surfaces using simple
empirical or theoretical models. The recommended procedures are outlined in
the Handbook of Urban Rail Noise and Vibration Control.
(44)
The approach
consists of adding the following adjustments to the 1/3-octave band spectrum of
the projected ground-borne vibration:
Building response or coupling loss – This adjustment represents
the change in the incident ground-borne vibration due to the presence
of the building foundation. The adjustments described in the handbook
(44)
are shown in Figure 6-14. Note that the correction is zero when
estimating basement floor vibration or vibration of at-grade slabs.
Measured values may be used in place of these generic adjustments.
Transmission through the building – The vibration amplitude
typically decreases as the vibration energy propagates from the
foundation through the remainder of the building. The general
assumption is that vibration attenuates by 1 to 2 dB for each floor.
Floor resonances – Vibration amplitudes will be amplified because of
resonances of the floor/ceiling systems. For a typical wood-frame
FEDERAL TRANSIT ADMINISTRATION 163
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
residential structure, the fundamental resonance is usually in the 15 to
20 Hz range. Reinforced-concrete slab floors in modern buildings will
have fundamental resonance frequencies in the 20 to 30 Hz range. An
amplification resulting in a gain of approximately 6 dB should be used in
the frequency range of the fundamental resonance.
Floor vibration and ground-borne noise – The projected floo
r
v
ibration is used to estimate the levels of ground-borne noise. T
he
pr
imary factors affecting noise level are the average vibration level
of
t
he room surfaces and the amount of acoustical absorption within th
e
room. The radiation adjustment is -5 dB for typical rooms,
(37) (50)
which
g
ives
:
Eq. 6-8
where:
= A-weighted sound level in a 1/3-octave band
= rms vibration velocity level in that band
= A-weighting adjustment at the 1/3-octave band center
frequency
The A-weighted levels in the 1/3-octave bands are combined to produce the
overall A-weighted sound level.
₋
Figure 6-14 Foundation Response for Various Types of Buildings
Where detailed information on the structural features of individual buildings are
unavailable and there are no site-specific data on outdoor to indoor propagation
characteristics, the preferred approach is to apply a combined factor for the
foundation response and the gain from floor resonances. Empirical data based
on the TCRP D-12 Project from 34 measurement sites across 5 cities in North
FEDERAL TRANSIT ADMINISTRATION 164
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
America and other studies suggest that the average change in vibration from
outdoor to indoor was 0 dB across all 1/3-octave bands with a standard
deviation of approximately 5 to 6 dB in the 31.5 to 63 Hz frequency.
(43)(48)
Therefore, the recommended approach for predicting indoor vibration based on
outdoor data is to use an adjustment of +3 to +6 dB for light-weight, wood-
frame construction and use an adjustment of 0 dB for heavier buildings.
However, for buildings with high-vibration sensitivity or where there is concern
regarding interference with vibration-sensitive equipment, it is advisable to
measure the outdoor-indoor response of the building, using the process
described in Section 2b or 2c, to determine the actual response of the
foundation and building to vibration.
Step 3: Assess Vibration Impact
Take inventory of vibration-sensitive land uses with impact.
Assess vibration impact at each receiver of interest using the impact criteria in
Section 6.3. Note that ground-borne vibration and noise levels that exceeded
criteria in the General Vibration Assessment may not cause impact according to
the more detailed procedures of the Detailed Vibration Analysis; in which case,
mitigation is not required. But if projected levels still exceed the criteria,
evaluate vibration mitigation measures using the spectra provided by the
Detailed Vibration Analysis.
Step 4: Determine Vibration Mitigation Measures
Select practical vibration control measures that will be effective at the dominant
vibration frequencies and compatible with the given transit structure and track support
system.
The purpose of vibration mitigation is to minimize the adverse effects that the
project ground-borne vibration and ground-borne noise will have on sensitive
land uses. Because ground-borne vibration is not as common a problem as
environmental noise, the mitigation approaches have not been as well defined. In
some cases it may be necessary to develop innovative approaches to control the
impact. See Appendix G for information on using non-standard methods.
Standard vibration control measures for rail transit systems are discussed in this
step. Note that vibration control measures for rail transit systems are not
always effective for freight trains.
(
xiv
)
Bus systems rarely cause vibration impact,
but if impact occurs, roadway roughness or unevenness caused by bumps, pot
holes, expansion joints, or driveway transitions are usually the causes.
Smoothing the roadway surface is typically the recommended course of
action.
(
xv
)
xiv
The heavy axle loads associated with freight rail are outside the range of applicable design parameters for vibration reduction
on lighter rail transit systems. Plans to relocate existing railroad tracks closer to vibration-sensitive sites in order to
accommodate a new rail transit line in the ROW must be carefully considered because it may not be possible to mitigate the
increased vibration impact from freight trains.
xv
In cases where a rubber-tired system runs inside a building, such as an airport people mover, vibration control may involve
additional measures. Loading and unloading of guideway support beams may generate dynamic forces that transmit into the
building structure. Special guideway support systems may be required, similar to the discussion below regarding floating slabs.
FEDERAL TRANSIT ADMINISTRATION 165
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Vibration reduction measures incur additional costs to a system. Some of the
same treatments for noise mitigation can be considered for vibration mitigation.
Costs for noise control measures are documented in a report from the Transit
Cooperative Research Program (TCRP).
(31)
Where applicable to vibration
reduction, costs for noise abatement methods from that report are given in the
following sections. These costs reflect the noise mitigation costs as of 1997
(unless otherwise noted), and should only be used as representative estimates
when considering noise mitigation options. Current noise mitigation costs
should be researched before decisions on noise mitigation options are finalized,
and then they should be documented according to Section 8.
Mitigation of vibration impacts may involve treatments at the source, along the
source-to-receiver propagation path, or at the receiver.
1a. Evaluate Source Treatments – The most effective vibration mitigation
treatments are applied at the vibration source. This is the preferred approach to
mitigation when possible. Possible source treatments include:
Preventative Maintenance – Effective maintenance programs are
essential for controlling ground-borne vibration. Key vibration points
are discussed below; see Section 4.5, Step 7 for more detailed
information on the benefits of effective maintenance programs on
controlling transit noise and vibration. While these are not mitigation
measures in the traditional sense, and should not be included as
mitigation in an environmental document, they can help to keep both
noise and vibration levels at a “like-new” level or reduce both in
systems with deferred maintenance.
Rail grinding is a particularly important practice for vibration
mitigation for rail that develops corrugations. The TCRP report
notes that periodic rail grinding results in a net savings per year on
wheel and rail wear. Most transit systems contract out rail grinding,
although some of the larger systems make the investment and do
their own grinding. As mentioned in Section 4.5, Step 7, the typical
rail grinding cost would be $1000 to $7000 per grinding pass mile,
with an additional investment of approximately $1 million for the
equipment for a larger transit system to do its own grinding.
Dramatic vibration reduction results can be achieved by
removing wheel flats through wheel truing. As mentioned in
Section 4.5, Step 7, a wheel truing machine costs approximately $1
million, including associated maintenance, materials, and labor costs.
The TCRP report figures a system with 700 vehicles would incur a
yearly cost of $300,000 to $400,000 for a wheel truing program.
Profile grinding of the rail head in combination with a wheel
truing program may be the most practical approach to controlling
and reducing vibration and noise where such practices are not
normally conducted. Profiles should be defined during the design
phase and should be in place when system opens.
(32)
The cost of
FEDERAL TRANSIT ADMINISTRATION 166
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
wheel and rail profile matching may be incorporated in the new
vehicle and new rail costs.
Rough wheels or rails can increase vibration levels by as much as 20
dB in extreme cases, negating the effects of even the most effective
vibration control measures. Yet, it is rare that vibration control
measures (such as those discussed below) will provide more than
15 to 20 dB attenuation. When there are ground-borne vibration
impacts with existing transit equipment, the best vibration control
measure often is to implement new or improved maintenance
procedures. Grinding rough or corrugated rail and wheel truing to
eliminate wheel flats and restore the wheel contour may provide
considerable vibration reduction. Regular maintenance may replace
the need to modify the existing track system, such as through
adding floating slabs.
Planning and Design of Special Trackwork – A large percentage
of
t
he vibration impact from a new transit facility is often caused by whee
l
impa
cts at special trackwork for turnouts and crossovers.
When
fea
sible, the most effective vibration control measure is to relocate t
he
s
pecial trackwork to a less vibration-sensitive area. This may requir
e
a
djusting the location by several hundred feet provided it will not hav
e
a
n adverse impact on the operation plan for the system. Careful rev
iew
of
crossover and turnout locations during the project develop
ment
pha
se is an important step to minimizing potential for vibration impact
.
Another approach is to use special devices (frogs) at turnouts and
crossovers that incorporate mechanisms to close the gaps between
running rails. Frogs with spring-loaded mechanisms and frogs with
movable points can substantially reduce vibration levels near crossovers.
According to the TCRP report, a spring frog costs about $12,000, twice
the cost of a standard frog. A movable point frog involves elaborate
signal and control circuitry resulting in higher costs at approximately
$200,000.
Vehicle Specifications – The ideal rail vehicle with respect t
o
minimizing ground-borne vibration should have the following
c
haracteristics
:
Low, unsprung weight
Soft
primary suspens
ion
A m
inimum of metal-to-metal contact between moving parts
of
t
he truc
k
S
mooth wheels that are perfectly roun
d
A li
mit for the vertical resonance frequency of the primary suspension
should be included in the specifications for any new vehicle. A vertical
resonance frequency of 12 Hz or less is sufficient to control the levels
of ground-borne vibration, although some have recommended the
vertical resonance frequency be less than 8 Hz.
FEDERAL TRANSIT ADMINISTRATION 167
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Special Track Support Systems – When the vibration assessment
indicates that vibration levels will be excessive, the track support system
is t
ypically modified to reduce the vibration levels
.
Fl
oating slabs, resiliently supported ties, high-resilience fasteners, a
nd
ba
llast mats can be used to reduce the levels of ground-borne vibrat
ion.
T
o be effective, all of these measures must be optimized for t
he
fr
equency spectrum of the vibration. Most of these relatively standar
d
pr
ocedures have been successfully used on several subway projects
.
Applications on at-grade and elevated track are less common. This is
bec
ause vibration impact is less common for at-grade and elevat
ed
track. Note that the cost of these types of vibration control measures is
a
higher percentage of the overall construction costs for at-grade a
nd
elevated track, and exposure to the elements can require substantial
design modifications.
Ea
ch major vibration control measure for track support is discuss
ed
below.
Costs for these treatments are not covered by the TCRP report
,
but
are given as estimates based on transit agency experienc
e.
R
esilient fasteners – Resilient fasteners are used to fasten t
he
r
ail to concrete track slabs. Standard resilient fasteners are ver
y
s
tiff in the vertical direction, usually in the range of 20
0,000
lb/in,
and do provide some vibration reduction compared to t
he
r
igid fastening systems used on older systems (e.g., wood half-
ties embedded in concrete).
S
pecial fasteners with vertical stiffness in the range of
30,000
lb/in
may reduce vibration by as much as 5 to 10 dB a
t
fr
equencies above 30 to 40 Hz. These premium fasteners var
y
in
cost and can be priced competitively when purchased in larg
e
qua
ntities
.
Ballast
mats – A ballast mat consists of a rubber or other ty
pe
of
elastomer pad that is placed under the ballast. In general, t
he
mat must be placed on a concrete pad to be effective. They will
not
be as effective if placed directly on the soil or the sub-
ballast. Consequently, most ballast mat applications are in
s
ubway or elevated structures
.
Ball
ast mats can provide 8 to 12 dB attenuation at frequenc
ies
a
bove 25 to 30 Hz.
(
58
)
Ballast mats are often a good retrofit
mea
sure for existing tie-and-ballast track where there
is
vibration impact. Installed ballast mats cost approximately $180
per
track-foot
.
Und
ertie pads – Undertie pads (resiliently supporte
d
c
oncrete ties) consist of a rubber pad mounted on the bott
om
of
a concrete tie directly on the ballast. The pads prov
ide
v
ibration isolation at frequencies above 25 Hz and are easy t
o
FEDERAL TRANSIT ADMINISTRATION 168
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
install or retrofit. Installed undertie pads cost approximately
$260 per track-foot.
Resiliently supported ties – The resiliently supported t
ie
s
ystem consists of concrete ties supported by rubber pa
ds
r
esting on top of a slab track or subway invert. The rails ar
e
fa
stened directly to the concrete ties using standard rail clips
.
R
esiliently supported ties provide vibration reduction i
n
bet
ween 15 to 40 Hz, which is particularly appropriate
for
t
ransit systems with vibration impact in the 20 to 30 Hz rang
e.
A resiliently supported tie system costs approximately $400 per
t
rack-foot
.
F
loating slabs – Floating slabs can be very effective a
t
controlling ground-borne vibration and noise and consist of a
concrete slab supported on resilient elements such as rubber or
a
similar elastomer. Floating slabs are effective at frequenc
ies
g
reater than their single-degree-of-freedom vertical resonanc
e
fr
equency
.
Fl
oating slabs are among the most expensive vibration control
treatments. A typical double-tie floating slab system costs
approximately 4 times the cost of ballast and tie per track foot.
Examples of floating slabs include:
- Floating slabs used in Washington, DC; Atlanta, GA; and
Boston, MA, were all designed to have a vertical
resonance in the 14 to 17 Hz range.
- A special system referred to as the double-tie system
was first used in Toronto. It consists of 5-foot-long
slabs with four or more rubber pads under each slab.
This system was designed with a resonance frequency in
the 12 to 16 Hz rang3.
- Another special floating slab was used in San Francisco’s
Bay Area Rapid Transit (BART) system. It uses a
discontinuous precast concrete double-tie system with
a resonance frequency in the 5 to 10 Hz frequency
range.
Tire-derived aggregate (TDA) – TDA (shredded tires) consists
of
a layer of tire shreds wrapped in geotech fabric plac
ed
under
neath the ballast on hard packed ground. This is a new, low-
cost option that can provide reduction in vibration levels a
t
fr
equencies above 25 Hz. This mitigation measure has proven to b
e
effec
tive for the Denver Regional Transportation District (RT
D)
li
ght rail system as well as the Santa Clara Valley Transportatio
n
A
uthority (VTA) light rail system,
(
59
)
but the effective life of TDA
ha
s not been determined. Installed TDA costs approximately $
260
per track-foot.
O
ther treatments – Changing any feature of the track s
upport
s
ystem can change the levels of ground-borne vibration. Approac
hes
FEDERAL TRANSIT ADMINISTRATION 169
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
such as using heavier rail, thicker ballast, or heavier ties can be
expected to reduce the vibration levels. There also is some
indication that vibration levels are lower with wood ties compared
to concrete ties. But there is little confirmation that any of these
approaches will make a substantial change in the vibration levels.
Operational Changes – The most effective operational change is t
o
r
educe the vehicle speed. Reducing the train speed by a factor of tw
o
wi
ll reduce vibration levels approximately 6 dB. Other operati
onal
c
hanges inc
lude:
Use of equipment that generates the lowest vibration levels during
t
he nighttime hours when people are most sensitive to vibration a
nd
noise.
A
djusting nighttime schedules to minimize movements in the m
ost
sensitive hours.
While
there are tangible mitigation benefits from speed reductions and
limits on operations during the most sensitive time periods, FTA does not
generally accept speed reduction as a vibration mitigation measure for two
important reasons: (1) speed reduction is unenforceable and negated if
vehicle operators do not adhere to established policies, and (2) it is
contrary to the purpose of the transit investment by FTA, which is to move
as many people as possible as efficiently and safely as possible. FTA does not
recommend limits on operations as a way to reduce vibration impacts.
1b. Evaluate Path Treatments – When vibration mitigation treatments
cannot be applied at the vibration source or additional mitigation is required
after treating the source, the next preferred placement of vibration mitigation is
along the vibration propagation path between the source and receiver. Possible
path treatments include:
Trenches – Use of trenches to control ground-borne vibration
is
a
nalogous to controlling airborne noise with noise barriers. T
his
a
pproach has not received much attention in the United States, bu
t
t
renches could be a practical method for controlling transit vibrat
ion
fr
om at-grade track. A rule-of-thumb given by Richert and Hall
(
60
)
is that
if
the trench is located close to the source, the trench bottom must
be
a
t least 0.6 times the Rayleigh wavelength below the vibration sourc
e.
For mo
st soils, Rayleigh waves travel at around 600 ft/sec, which mea
ns
t
hat the wavelength at 30 Hz is 20 ft, requiring that a trench
be
a
pproximately 15 ft deep to be effective at 30 Hz
.
A t
rench can be effective as a vibration barrier if it is either open or
solid. The Toronto Transit Commission tested a trench filled with
Styrofoam to keep it open and reported successful performance over a
period of at least one year. Solid barriers can be constructed with sheet
piling or concrete poured into a trench.
Buffer Zones – Expanding the rail ROW can be the most economica
l
method of reducing the vibration impact by simply increasing the
dis
tance between the source and receiver. A similar approach is t
o
FEDERAL TRANSIT ADMINISTRATION 170
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
negotiate a vibration easement from the affected property owners (e.g.,
a row of single-family homes adjacent to a proposed commuter rail
line). There may be legal limitations, however, on the ability of funding
agencies to acquire land strictly for the purpose of mitigating vibration
(or noise) impact.
1c. Evaluate Receiver Treatments – When vibration mitigation treatments
cannot be applied at the source or along the propagation path, or if
combinations of treatments are required, treatments to the receivers can be
considered as described below.
Building Modifications – In some circumstances, it is practical to
mo
dify the affected building to reduce the vibration level. Vibratio
n
isolation of buildings consists of supporting the building foundation on
ela
stomer pads, similar to bridge bearing pads. Vibration isolation
of
buildings is seldom an option for existing buildings and is typically only
possible for new construction. Vibration impacts on sensitive laboratory
ins
truments, such as electron microscopes, may be controlled wit
h
v
ibration isolation tables
.
T
his approach is particularly important for shared-use facilities such as
an office space above a transit station or terminal. When vibration-
sensitive equipment such as electron microscopes will be affected by
transit vibration, specific modifications to the building structure may be
the most cost-effective method of controlling the impact aside from
modification of equipment mounting systems. For example, the floor
upon which the vibration-sensitive equipment is located could be
stiffened and isolated from the remainder of the building to reduce the
vibration. Alternatively, the equipment mounting systems could be
modified or the equipment could be relocated to a different building at
far less cost.
FEDERAL TRANSIT ADMINISTRATION 171
SECTION
7
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Noise and Vibration during
Construction
Construction noise and vibration often generates complaints from the
community, even when construction is for a limited timeframe. Public concerns
about construction noise and vibration increase considerably with lengthy
periods of heavy construction on major projects as well as prevalence of
nighttime construction (often scheduled to avoid disrupting workday road and
rail traffic). Noise and vibration complaints typically arise from interference with
people's activities, especially when the adjacent community has no clear
understanding of the extent or duration of the construction. Misunderstandings
can arise when the community thinks a contractor is being insensitive, and the
contractor believes it is performing the work in compliance with local
ordinances. This situation underscores the need for early identification and
assessment of potential problem areas.
This section outlines the procedures for assessing noise and vibration impacts
during construction. The type of assessment (qualitative or quantitative) and the
level of analysis are determined based on the scale of the project and
surrounding land uses. In cases where a full quantitative assessment is not
warranted, a qualitative assessment of the construction noise and vibration
environment can lead to greater understanding and tolerance in the community.
For major projects with extended periods of construction at specific locations, a
quantitative assessment can aid contractors in making bids by allowing changes
in construction approach and including mitigation costs before the construction
plans are finalized.
Generally, local noise ordinances are not very useful for evaluating construction
noise impact. They usually relate to nuisance and hours of allowed activity, and
sometimes specify limits in terms of maximum levels, but are generally not
practical for assessing the impact of a construction project. Project construction
noise criteria should take into account the existing noise environment, the
absolute noise levels during construction activities, the duration of the
construction, and the adjacent land uses. While it is not the purpose of this
manual to specify standardized criteria for construction noise impact, the
following guidelines can be considered reasonable criteria for assessment. If
these criteria are exceeded, there may be adverse community reaction.
Procedures for assessing construction noise are presented in Section 7.1.
Procedures for assessing construction vibration are presented in Section 7.2.
7.1 Construction Noise Assessment
Noise impacts from construction may vary greatly depending on the duration
and complexity of the project. The key elements of the Construction Noise
Assessment procedure and recommended workflow are as follows.
FEDERAL TRANSIT ADMINISTRATION 172
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Step 1: Determine Level of Construction Noise Assessment
Step 2: Use a Qualitative Construction Noise Assessment to Estimate
Construction Noise
Step 3: Use a Quantitative Construction Noise Assessment to Estimate
Construction Noise
Step 4: Assess Construction Noise Impact
Step 5: Determine Construction Noise Mitigation Measures
If there is uncertainty in how to determine the appropriate level of assessment,
contact the FTA Regional office.
Step 1: Determine Level of Construction Noise
Assessment
Determine the appropriate level of assessment based on the scale and type of the
project and depending on the stage of environmental review.
Consider the following factors:
Scale of the projec
t
Pr
oximity of noise-sensitive sites to the construction z
ones
Number
of noise-sensitive receivers in the project are
a
Dur
ation of construction activities near noise-sensitive receiver
s
Sc
hedule, including the construction days, hours, and time per
iods
Met
hod (e.g., cut-and-cover vs. bored tunneling
)
Concern about construction noise expressed in comments by the
g
eneral public (e.g., through scoping or public meeting
s)
1a
. Determine if an assessment is required – Construction Noise
Assessments are not required for many small projects including:
Installation of safety features like grade-crossing signals
;
T
rack improvements within the ROW;
or
Er
ecting small buildings and facilities which are similar in scale to t
he
s
urrounding development
.
For
small projects like these, include descriptions in the environmental
document of the length of construction, the loudest equipment to be used, the
expected truck access routes, the avoidance of nighttime activity, and any other
relevant planned construction method.
1b. Determine whether a qualitative or quantitative assessment is
required
Qualitative Construction Noise Assessment – Qualitative
Cons
truction Noise Assessments may be required for projects with les
s
t
han a month of construction time in a noise-sensitive area. See Step
2
for mo
re information on Qualitative Construction Noise Assessments
.
FEDERAL TRANSIT ADMINISTRATION 173
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Quantitative Construction Noise Assessments – Quantitative
Construction Noise Assessments may be required for projects with a
month or more of construction in noise-sensitive areas or if particularly
noisy equipment will be involved. See Step 3 for more information on
Quantitative Construction Noise Assessments.
Step 2: Use a Qualitative Construction Noise Assessment
to Estimate Construction Noise
Use a qualitative construction noise assessment to estimate construction noise for
appropriate projects per Section 7.1, Step 1b.
Provide qualitative descriptions in the environmental document of the following
elements:
Duration of construction (both overall and at specific locations)
Equipment expected to be used (e.g., noisiest equipment)
Schedule with limits on times of operation (e.g., daytime use only)
Monitoring of noise
Forum for communicating with the public
Commitments to limit noise levels to certain levels, including any local
ordinances that apply
Consideration of application of noise control treatments used
successfully in other projects
Effective community outreach and relations are important for these projects.
Disseminate information to the public early regarding the kinds of construction
equipment, expected noise levels, and durations to forewarn potentially affected
neighbors about the temporary inconvenience. Including a general description of
the variation of noise levels during a typical construction day may also be
helpful.
Note that the construction criteria in Step 4 do not apply to qualitative
assessments.
Step 3: Use a Quantitative Construction Noise Assessment
to Estimate Construction Noise
Use a quantitative construction noise assessment to estimate construction noise for
appropriate projects per Section 7.1, Step 1b.
For Quantitative Construction Noise Assessments, follow the recommended
procedure in this step and include a description of the planned construction
methods and any basic measures that have been identified to reduce the
potential impact, such as prohibiting the noisiest construction activities during
the nighttime, in the environmental document. It may be prudent, however, to
defer final decisions on noise control measures until the project and
construction plans are defined in greater detail during the engineering phase.
Noise Source Levels from Typical Construction Equipment
and Operations – The noise levels generated by construction
FEDERAL TRANSIT ADMINISTRATION 174
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
equipment vary greatly on factors such as the type of equipment, the
equipment model, the operation being performed, and the condition of
the equipment. Typically, the dominant source of noise from most
construction equipment is the engine, often a diesel engine, which
usually does not have sufficient muffling. In other cases, such as impact
pile-driving or pavement-breaking, noise generated by the process
dominates. Construction equipment can be considered to operate in
the following two modes for Construction Noise Assessments:
Stationary – Stationary equipment operates in one location
for
one
or more days at a time, with either a fixed power operat
ion
(pumps, generators, compressors) or a variable noise operation
(
pile drivers, pavement breakers)
.
Mobile – Mobile equipment moves around the construction site
wi
th power applied in cyclic fashion (bulldozers, loaders), or to an
d
from the site (trucks). Movement around the site is considered in
the construction noise prediction procedure.
V
ariation in power imposes additional complexity in characterizing the noise
source level from mobile equipment. Describe the noise at a reference distance
from the equipment operating at full power and adjusting it based on the duty
cycle of the activity to determine the L
eq(t)
of the operation.
Typical noise levels from representative equipment are included in Table 7-1.
The levels are based on an EPA Report,
(
61
)
measured data from railroad
construction equipment taken during the 1976 Northeast Corridor
Improvement Project, the FHWA Roadway Construction Noise Model, and
other measured data.
For equipment that is not represented in Table 7-1, measure the noise levels
according to the standard procedures for measuring the exterior noise levels
for the certification of mobile and stationary construction equipment by the
Society of Automotive Engineers.
(
62
)(
63
)
FEDERAL TRANSIT ADMINISTRATION 175
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Table 7-1 Construction Equipment Noise Emission Levels
Equipment
Typical Noise Level 50 ft
from Source, dBA
Air Compressor
80
Backhoe
80
Ballast Equalizer
82
Ballast Tamper
83
Compactor
82
Concrete Mixer
85
Concrete Pump
82
Concrete Vibrator
76
Crane, Derrick
88
Crane, Mobile
83
Dozer
85
Generator
82
Grader
85
Impact Wrench
85
Jack Hammer
88
Loader
80
Paver
85
Pile-driver (Impact)
101
Pile-driver (Sonic)
95
Pneumatic Tool
85
Pump
77
Rail Saw
90
Rock Drill
95
Roller
85
Saw
76
Scarifier
83
Scraper
85
Shovel
82
Spike Driver
77
Tie Cutter
84
Tie Handler
80
Tie Inserter
85
Truck
84
3a. Use the metric L
eq(t)
to assess construction noise. This unit is appropriate
because L
eq(t)
can be used to describe:
Noise level from operation of each piece of equipment separately, and
levels can be combined to represent the noise level from all equipment
operating during a given period
Noise level during an entire phase
Average noise over all phases of the construction
3b. Use Eq. 7-1 to predict construction noise impact for major transit projects,
considering the noise generated by the equipment and noise propagation due to
distance. Calculate
for all equipment individually, then use decibel
addition to sum the
for all equipment operating during the same time
period. See Appendix B.1.1 for information on decibel addition.
FEDERAL TRANSIT ADMINISTRATION 176
Eq. 7-1
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
where:
=
at a receiver from the operation of a single piece of
equipment over a specified time period, dBA
= noise emission level of the particular piece of equipment at
the reference distance of 50 ft, dBA
= usage factor to account for the fraction of time that the
equipment is in use over the specified time period
= distance from the receiver to the piece of equipment, ft
= a constant that accounts for topography and ground effects
Determine the quantities for Eq. 7-1 based on the level of assessment as
described below.
A general assessment of construction noise is warranted for projects i
n
an early assessment stage when the equipment roster and schedule are
undefined
and only a rough estimate of construction noise levels
is
pr
actica
l.
A det
ailed analysis of construction noise is warranted when many noise-
sensitive sites are adjacent to a construction project or wher
e
c
ontractors are faced with stringent local ordinances or heighte
ned
publi
c concerns expressed in early outreach efforts
.
Complet
e the appropriate assessment for each phase of construction. Major
construction projects are accomplished in several different phases. Each phase
has a specific equipment mix, depending on the work to be accomplished during
that phase. As a result of the equipment mix, each phase has its own noise
characteristics; some phases have higher continuous noise levels than others,
and some have higher impact noise levels than others.
Option A: General Assessment – Determine the quantities for Eq. 7-1
based on the following assumptions for a General Assessment of each phase of
construction.
Noise emission level (
) – Determine the emission level at
50
ft according to noise from typical construction equipment descr
ibed
a
bove and Table 7-
1.
Usag
e factor (
) – Assume a usage factor of 1. This assumes a
t
ime period of one-hour with full power operation. Most construct
ion
equipmen
t operates continuously for periods of one-hour or mor
e
dur
ing the construction per
iod.
T
herefore, 10log(Adj
usage
) = 0 and can be omitted from the equation.
Distance (D) – Assume that all equipment operates at the center of
t
he project, or centerline for guideway or highway construction project
.
FEDERAL TRANSIT ADMINISTRATION 177
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Ground effect (G) – G = 0 assuming free-field conditions and ignoring
ground effects. If ground effects are of specific importance to the
assessment, consider using the Detailed Analysis procedure.
Only determine the
for the two noisiest pieces of equipment
expected to be used in each phase of construction. Then, sum the levels for
each phase of construction using decibel addition.
Option B: Detailed Analysis – Determine the quantities for Eq. 7-1 based on
the following assumptions for a Detailed Analysis of each phase of construction.
Alternatively, for detailed, long-term, and complex construction projects or
projects near a particularly sensitive site, the FHWA’s Windows-based
screening tool, “Roadway Construction Noise Model (RCNM),” can be used for
the prediction of construction noise.
(
64
)
Noise emission level (
) – Measure or certify the noise
emission level for each piece of equipment.
Usage factor (
) – Long-term construction project noise
impact is based on a 30-day average L
dn
, the times of day of construction
activity (nighttime noise is penalized by 10 dB in residential areas), and
the percentage of time the equipment is used during a period of time
that will affect
.
For example, an 8-hour L
eq(t)
is determined by making
the
percentage of time each individual piece of equipment operates under
full power in that period. Similarly, the 30-day average L
dn
is determined
from the
expressed by the percentage of time the equipment
is used during the daytime hours (7 a.m. to 10 p.m.) and nighttime (10
p.m. to 7 a.m.), separately, over a 30-day period. To account for
increased sensitivity to nighttime noise, the nighttime noise levels are
adjusted by 10 dB in the L
dn
computation (see Appendix B.1.4.5).
Distance (D) – Determine the location of each piece of equipment
during operation and the distance to each receiver.
Ground effect (G) – Use Table 4-26 in Section 4.5, Step 3 to calculate
G to account for the site topography, natural and man-made barriers,
and ground effects.
Compute the 8-hour L
eq(t)
(
) and the 30-day average L
dn
(
for all equipment expected to be used in each phase
of construction separately. Then, sum the levels for each phase of
construction using Eq. 4-56 and Eq. 4-57 in Table 4-32.
Step 4: Assess Construction Noise Impact
Compare the predicted noise levels from the Quantitative Construction Noise
Assessment with impact criteria to assess impact from construction noise for each
phase of construction.
FEDERAL TRANSIT ADMINISTRATION 178
Table 7-2 General Assessment Construction Noise Criteria
, dBA
Land Use
Day
Night
Residential
90
80
Commercial
100
100
Industrial
100
100
Table 7-3 Detailed Analysis Construction Noise Criteria
Land Use
dBA
Day
Night
, dBA
30-day Average
Residential
80
70
75
Commercial
85
85
80
*
Industrial
90
90
85
*
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
No standardized criteria have been developed for assessing construction noise
impact. Consequently, criteria must be developed on a project-specific basis
unless local ordinances apply. As stated earlier in this section, local noise
ordinances are typically not very useful in evaluating construction noise. They
usually relate to nuisance and hours of allowed activity, and sometimes specify
limits in terms of maximum levels, but are generally not practical for assessing
the impact of a construction project. Project construction noise criteria should
account for the existing noise environment, the absolute noise levels during
construction activities, the duration of the construction, and the adjacent land
use. While it is not the purpose of this manual to specify standardized criteria
for construction noise impact, the following guidelines can be considered
reasonable criteria for assessment. If these criteria are exceeded, there may be
adverse community reaction.
The construction impact guidelines are presented based on the level of
quantitative assessment.
Option A: General Assessment – Compare the combined
for
the two noisiest pieces of equipment for each phase of construction determined
in Section 7.1, Step 3 to the criteria below. Then, identify locations where the
level exceeds the criteria.
Option B: Detailed Analysis – Compar
e the combined
and the
combined
for all equipment for each phase of construction
determined in Section 7.1, Step 3 to the criteria below. Then, identify locations
where the level exceeds the criteria.
*Use a 24-hour L
eq(24hr)
instead of L
dn.equip(30day)
.
Step 5: Determine Construction Noise Mitigation
Measures
Evaluate the need for mitigation and select appropriate mitigation measures.
FEDERAL TRANSIT ADMINISTRATION 179
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Where potential impacts have been identified according to Section 7.1, Step 4,
evaluate appropriate control measures. Include descriptions of how each
affected location will be treated with one or more mitigation measures in the
environmental document.
5a. Determine the appropriate approach for construction noise control.
Categories of approaches include:
Design considerations and project layout
Construct noise barriers, such as temporary walls or piles of
excavated material, between noisy activities and noise-sensitive
receivers.
Re-route truck traffic away from residential streets. Select streets
with the fewest homes if no alternatives are available.
Site equipment on the construction lot as far away from noise-
sensitive sites as possible.
Construct walled enclosures around especially noisy activities or
clusters of noisy equipment. For example, shields can be used
around pavement breakers, and loaded vinyl curtains can be draped
under elevated structures.
Sequence of operations
Combine noisy operations to occur in the same time period. The
total noise level produced will not be substantially greater than the
level produced if the operations were performed separately.
Avoid nighttime activities. Sensitivity to noise increases during the
nighttime hours in residential neighborhoods.
Alternative construction methods
Avoid impact pile-driving where possible in noise-sensitive areas.
Drilled piles or the use of a sonic/vibratory pile driver or push pile
driver are quieter alternatives where the geological conditions
permit their use.
Use specially-quieted equipment, such as quieted and enclosed air
compressors and properly-working mufflers on all engines.
Select quieter demolition methods. For example, sawing bridge
decks into sections that can be loaded onto trucks results in lower
cumulative noise levels than impact demolition by pavement
breakers.
Include descriptions of how each impacted location will be treated with one
or more mitigation measures in the environmental impact assessment when
possible.
5b. Describe and commit to a mitigation plan that will be developed later when
the information is available to make final decisions (not often available during the
project development phase) on all specific mitigation measures. This may be the
case for large, complex projects. The objective of the plan should be to
minimize construction noise using all reasonable (e.g., cost vs. benefit) and
feasible (e.g., possible to construct) means available.
FEDERAL TRANSIT ADMINISTRATION 180
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Components of a mitigation plan may include some or all of the following
provisions, which should also be specified in construction contracts:
Equipment noise emission limits – Equipment noise limits ar
e
a
bsolute noise limits applied to generic classes of equipment at
a
r
eference distance (typically 50 ft). The limits should be set no hig
her
t
han what is reasonably achievable for well-maintained equipment wit
h
effec
tive mufflers. Lower limits that require source noise control may
be
a
ppropriate for certain equipment when needed to minimize communit
y
nois
e impact, if reasonable and feasible. Provisions could also
be
included to require equipment noise certification testing prior to use
on-
s
ite.
Lot-
line construction noise limits – Lot-line construction nois
e
limits are noise limits that apply at the lot-line of specific noise-sensitive
properties. The limits are typically specified in terms of both noise
exposur
e (usually L
eq(t)
over a 20-30-minute period) and maximum noise
lev
el. They should be based on local noise ordinances if applicable, a
s
well as pre-construction baseline noise levels (usually 3 to 5 dB above
t
he baseline)
.
O
perational and/or equipment restrictions – It may be necessar
y
t
o prohibit or restrict certain construction equipment and activ
ities
nea
r residential areas during nighttime hours. This is particularly tr
ue
for ac
tivities that generate tonal, impulsive, or repetitive sounds, such a
s
ba
ck-up alarms, hoe ram demolition, and pile-driving
.
Noise abatement requirements – In some cases, specifications may
be provided for particular noise control treatments based on the results
of
the design analysis and/or prior commitments made to the public
by
c
ivic authorities. An example would be the requirement for a temporar
y
nois
e barrier to shield a particular community area from nois
y
c
onstruction activities
.
N
oise monitoring plan requirements – Plans can be developed
for
pr
e-project noise monitoring to establish baseline noise levels a
t
s
ensitive locations, as well as for periodic equipment and lot-line nois
e
monitoring during the construction period. The plan should outline the
mea
surement and reporting methods that will be used to demonstrat
e
compliance with the project noise limits.
Noise control plan requirements – For major construction
projects, preparation and submission of noise control plans on a
per
iodic basis (e.g., every six months) are generally required. Thes
e
plans should predict the construction noise at noise-sensitive receiver
loca
tions based on the proposed construction equipment and methods
.
If
the analysis predicts that the specified noise limits will be excee
ded,
t
he plan should specify the mitigation measures that will be applied a
nd
s
hould demonstrate the expected noise reductions these measures wi
ll
a
chieve. The objective of this proactive approach is to minimize th
e
FEDERAL TRANSIT ADMINISTRATION 181
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
likelihood of community noise complaints by ensuring that any
necessary mitigation measures are included in the construction plans.
Compliance enforcement program – If construction noise is a
n
is
sue in the community, it is important that a program be implement
ed
t
o monitor contractor compliance with the noise control specificatio
ns
a
nd mitigation plan. It is recommended that this function be performe
d
by
a construction management team on behalf of the public agency
.
P
ublic information and complaint response procedures – T
o
maintain positive community relations, it is recommended to keep the
publi
c informed about the construction plans and efforts to minimiz
e
noise, and procedures should be established for prompt response and
c
orrective action to noise complaints during construct
ion.
Most of these provisions are appropriate for large-scale projects, where
construction activity will continue for many months, if not years. The linked
references contain more information on construction noise for major
transportation projects.
(60)(
65
)
7.2 Construction Vibration Assessment
Construction activity can result in varying degrees of ground vibration,
depending on the equipment and methods employed. Operation of construction
equipment causes ground vibrations that spread through the ground and
diminish in strength with distance. Buildings founded on the soil near the
construction site respond to these vibrations with varying results, ranging from
no perceptible effects at the lowest levels, low rumbling sounds and perceptible
vibrations at moderate levels, and slight damage at the highest levels.
While ground vibrations from construction activities do not often reach the
levels that can damage structures, fragile buildings must receive special
consideration. The construction vibration criteria include consideration of the
building condition.
The key elements of the Construction Vibration Assessment procedures and
recommended workflow are as follows:
Step 1: Determine level of construction vibration assessment
Step 2: Use a qualitative construction vibration assessment
Step 3: Use a quantitative construction vibration assessment
Step 4: Assess construction vibration impact
Step 5: Determine construction vibration mitigation measures
FEDERAL TRANSIT ADMINISTRATION 182
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Step 1: Determine Level of Construction Vibration
Assessment
Determine the appropriate level of assessment based on the scale and type of the
project and the stage of environmental review.
1a. Determine if an assessment is required.
Construction Vibration Assessments are not required for many small projects
including:
Installation of safety features like grade-crossing signals
Track improvements within the ROW
Erecting small buildings and facilities, which are similar in scale to the
surrounding development
1b. Determine whether a qualitative or quantitative assessment is
required.
Qualitative Construction Vibration Assessment – A qualitative
construction vibration assessment is appropriate for projects where
prolonged annoyance or damage from construction vibration is not
expected. For example, equipment that generates little or no ground
vibration—such as air compressors, light trucks, and hydraulic loaders—
only require qualitative descriptions. See Section 7.2, Step 2 for more
information on qualitative construction vibration assessments.
Quantitative Construction Vibration Assessment – A
quantitative construction vibration analysis is appropriate for projects
where construction vibration may result in building damage or
prolonged annoyance. For example, activities such as blasting, pile-
driving, vibratory compaction, demolition, and drilling or excavation
near sensitive structures require a quantitative analysis. See Section 7.2,
Step 3 for more information on quantitative construction vibration
assessments.
If there is uncertainty in how to determine the appropriate level of assessment,
contact the FTA Regional office.
Step 2: Use a Qualitative Construction Vibration
Assessment
Use a qualitative construction vibration assessment to estimate vibration for
appropriate projects per Section 7.2, Step 1b.
Provide qualitative descriptions in the environmental document of the following
elements:
Duration of construction (both overall and at specific locations)
Equipment expected to be used
Description of how ground-borne vibration will be maintained at an
acceptable level
FEDERAL TRANSIT ADMINISTRATION 183
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Note that the criteria in Section 7.2, Step 4 do not apply to qualitative
assessments.
Step 3: Use a Quantitative Construction Vibration
Assessment
Use a quantitative construction vibration assessment to estimate vibration for
appropriate projects per Section 7.2, Step 1b.
For quantitative construction vibration assessments, follow the recommended
procedure in this step. Vibration source levels from typical construction
equipment and operations are provided below, and procedures on how to
estimate construction vibration for damage and annoyance are provided in Steps
3a and 3b, respectively.
Vibration Source Levels from Construction Equipment – Table
7-4 presents average source levels in terms of velocity for various types
of construction equipment measured under a wide variety of
construction activities. The approximate rms vibration velocity levels
were calculated from the PPV limits using a crest factor of 4,
representing a PPV-rms difference of 12 dB. Note that although the
table gives one level for each piece of equipment, there is considerable
variation in reported ground vibration levels from construction
activities. The data in Table 7-4 provide a reasonable estimate for a
wide range of soil conditions.
(
66
)(
67
)(
68
)(
69
)
Table 7-4 Vibration Source Levels for Construction Equipment
Equipment
PPV at 25
ft, in/sec
Approximate
Lv
*
at 25 ft
Pile Driver (impact)
upper range
1.518
112
typical
0.644
104
Pile Driver (sonic)
upper range
0.734
105
typical
0.17
93
Clam shovel drop (slurry wall)
0.202
94
Hydromill (slurry
wall)
in soil
0.008
66
in rock
0.017
75
Vibratory Roller
0.21
94
Hoe Ram
0.089
87
Large bulldozer
0.089
87
Caisson drilling
0.089
87
Loaded trucks
0.076
86
Jackhammer
0.035
79
Small bulldozer
0.003
58
*
RMS velocity in decibels, VdB re 1 micro-in/sec
3a. Damage Assessment
Assess for building damage for each piece of equipment individually.
Construction vibration is generally assessed in terms of peak particle velocity
(PPV), as described in Section 5.1.
FEDERAL TRANSIT ADMINISTRATION 184
Eq. 7-2
where:
= the peak particle velocity of the equipment
adjusted for distance, in/sec
= the source reference vibration level at 25 ft,
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Determine the vibration source level (PPV
ref
) for each piece of
equipment at a reference distance of 25 ft as described above and in
Table 7-4.
Use Eq. 7-2 to apply the propagation adjustment to the source
reference level to account for the distance from the equipment to the
receiver. Note that the equation is based on point sources with normal
propagation conditions.
in/sec
= distance from the equipment to the receiver, ft
3b. Annoyance Assessment
Assess for annoyance for each piece of equipment individually. Ground-borne
vibration related to human annoyance is related to rms velocity levels,
expressed in VdB as described in Section 5.1.
Estimate the vibration level (L
v
) using Eq. 7-3.
Eq. 7-3
where:
= the rms velocity level adjusted for distance, VdB
= the source reference vibration level at 25 ft, VdB
= distance from the equipment to the receiver, ft
Step 4: Assess Construction Vibration Impact
Compare the predicted vibration levels from the Quantitative Construction Vibration
Assessment with impact criteria to assess impact from construction vibration.
Assess potential damage effects from construction vibration for each piece of
equipment individually. Note that equipment operating at the same time could
increase vibration levels substantially, but predicting any increase could be
difficult. The criteria presented in this section should be used during the
environmental impact assessment phase to identify problem locations that must
be addressed during the engineering phase.
Compare the PPV and approximate L
v
for each piece of equipment determined
in Section 7.2, Step 3 to the vibration damage criteria in Table 7-5, which is
presented by building/structural category, to assess impact.
(
70
)(
71
)
The
approximate rms vibration velocity levels were calculated from the PPV limits
using a crest factor of 4.
FEDERAL TRANSIT ADMINISTRATION 185
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Table 7-5 Construction Vibration Damage Criteria
Building/ Structural Category
PPV, in/sec
*
Approximate L
v
I. Reinforced-concrete, steel or timber (no plaster)
0.5
102
II. Engineered concrete and masonry (no plaster)
0.3
98
III. Non-engineered timber and masonry buildings
0.2
94
IV. Buildings extremely susceptible to vibration damage
0.12
90
*
RMS velocity in decibels, VdB re 1 micro-in/sec
Compare the L
v
determined in Section 7.2, Step 3 to the criteria for the
General Vibration Assessment in Section 6.2 to assess annoyance or
interference with vibration-sensitive activities due to construction vibration.
Step 5: Determine Construction Vibration Mitigation
Measures
Evaluate the need for mitigation and select appropriate mitigation measures where
potential human impacts or building damage from construction vibration have been
identified according to Section 7.2, Step 4.
5a. Determine the appropriate approach for construction vibration mitigation
considering equipment location and processes.
Design considerations and project layout
Route heavily-loaded trucks away from residential streets. Select
streets with the fewest homes if no alternatives are available.
Operate earth-moving equipment on the construction lot as far
away from vibration-sensitive sites as possible.
Sequence of operations
Phase demolition, earth-moving, and ground-impacting operations
so as not to occur in the same time period. Unlike noise, the total
vibration level produced could be substantially less when each
vibration source operates separately.
Avoid nighttime activities. Sensitivity to vibration increases during
the nighttime hours in residential neighborhoods.
Alternative construction methods
Carefully consider the use of impact pile-driving versus drilled piles
or the use of a sonic/vibratory pile driver or push pile driver where
those processes might create lower vibration levels if geological
conditions permit their use.
- Pile-driving is one of the greatest sources of vibration associated
with equipment used during construction of a project. The
source levels in Table 7-4 indicate that sonic pile drivers may
provide substantial reduction of vibration levels compared to
impact pile drivers. But, there are some additional vibration
effects of sonic pile drivers that may limit their use in sensitive
locations.
- A sonic pile driver operates by continuously shaking the pile at a
fixed frequency, literally vibrating it into the ground. Continuous
operation at a fixed frequency may, however, be more
FEDERAL TRANSIT ADMINISTRATION 186
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
noticeable to nearby residents, even at lower vibration levels.
Furthermore, the steady-state excitation of the ground may
induce a growth in the resonant response of building
components. Resonant response may be unacceptable in cases
of fragile buildings or vibration-sensitive manufacturing
processes. Impact pile drivers, however, produce a high
vibration level for a short time (0.2 seconds) with sufficient time
between impacts to allow any resonant response to decay.
- Select demolition methods involving little to no impact, where
possible. For example, sawing bridge decks into sections that
can be loaded onto trucks results in lower vibration levels than
impact demolition by pavement breakers. Milling generates
lower vibration levels than excavation using clam shell or chisel
drops.
- Avoid vibratory rollers and packers near sensitive areas.
5b. Describe and commit to a mitigation plan that will be developed and
implemented during the engineering and construction phase when the
information available during the project development phase will not be sufficient
to define specific construction vibration mitigation measures. The objective of
the plan should be to minimize construction vibration damage using all
reasonable and feasible means available. The plan should include the following
components:
A procedure for establishing threshold and limiting vibration values f
or
pot
entially affected structures, based on an assessment of each structur
e’s
a
bility to withstand the loads and displacements due to construct
ion
vibrations
A c
ommitment to develop a vibration monitoring plan during t
he
eng
ineering phase and to implement a compliance monitoring progra
m
dur
ing constructi
on
FEDERAL TRANSIT ADMINISTRATION 187
SECTION
8
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Documentation of Noise and
Vibration Assessment
The level of required documentation is determined according to the project
class of action. Section 2.1 covers the appropriate class of action (EIS, EA, or
CE) for different projects. If there is uncertainty in the appropriate level of
documentation, contact the FTA Regional office.
The noise and vibration analysis must be articulated to the public in a clear,
comprehensive manner for all levels of documentation. The technical data and
information necessary to withstand scrutiny in the environmental review
process must be documented in a way that remains intelligible to the public.
Justification for all assumptions used in the analysis, such as selection of
representative measurement sites and all baseline conditions, must be presented
for review.
A separate technical report or memorandum is often prepared as a supplement
to the environmental document. A technical report is appropriate in cases when
including the data from the assessment would create an unreasonably long
environmental document. The details of the analysis are important for
establishing the basis for the assessment. Therefore, all details in the technical
report should be contained in a well-organized format for easy access to the
information.
For large-scale projects, the environmental document should contain a summary
of the essential analysis information to provide subject matter context and the
analysis findings. For these projects, separate technical reports are usually
prepared as supplements to the EIS or EA and referred to in the environmental
document. For smaller projects, or projects with minimal noise or vibration
impact, all of the technical information may be presented in the environmental
document itself or in a technical memorandum. Other projects might have no
potential for noise or vibration impacts. For those projects, that environmental
documentation should explain that no noise or vibration impacts are expected.
This section provides guidance on presenting the necessary noise and vibration
information in the environmental document (Section 8.1) and the associated
technical report (Section 8.2).
8.1 Environmental Document
In the environmental document, provide a summary of the comprehensive noise
and vibration information from the technical report and emphasize the salient
points of the analysis in a format and style that the public can understand.
Smaller projects may have all of the technical information contained within the
environmental document, so take special care in summarizing the technical
details to convey the information adequately.
FEDERAL TRANSIT ADMINISTRATION 188
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Step 1: Choose the Information to Include
Choose the appropriate noise and vibration analysis information to include based on
the level of environmental review and the associated documentation.
1a. Provide full disclosure of noise and vibration impacts in the
environmental document, including identification of locations where impacts
cannot be mitigated below the severe impact level. In general, an EIS describes
significant impacts and plans to mitigate the impacts. For EAs, completion of the
environmental review with a finding of no significant impact (FONSI) may
depend on mitigation being considered for incorporation in the proposed
project. The way mitigation is presented in the environmental document
depends on the type of impact (noise or vibration) and the stage of project
development and environmental review. Projects that meet the criteria of a CE
may also require the completion of a noise and/or vibration analysis, and the
results of such an analysis should be documented in a noise memo or the CE
documentation.
1b. Document noise impacts – Typically, airborne noise impacts can be
accurately predicted during the environmental review. For projects that focus
on a single alternative, noise impacts can be accurately identified in the draft
environmental document. If mitigation is anticipated, then mitigation options
should be explored in the EA or draft EIS; firm decisions on mitigation can be
deferred to the final document. But for all projects, decisions on noise
mitigation should be made before the final document is approved.
1c. Document vibration impacts – Predicting vibration impacts accurately is
more complex because ground-borne vibration may be strongly influenced by
subsurface conditions. The geotechnical studies that reveal these conditions are
normally undertaken during the engineering phase, after the environmental
review process is complete. Therefore, the final environmental document will
usually not be able to state with certainty whether mitigation is needed for
ground-borne vibration and noise.
If the engineering phase is conducted at the same time as the final environmental
document, report the results of the Detailed Vibration Analysis in the final
environmental document. If the engineering phase is conducted after the final
environmental document, report the results of the General Vibration
Assessment in the final environmental document. If impact is determined,
include a commitment in the final document to conduct a Detailed Vibration
Analysis during the engineering phase to complete the impact assessment. Also,
include a discussion on various control measures that could be used and the
likelihood that the criteria could be met through the use of one or more of the
measures. It may be possible to state a commitment in the final environmental
document to adhere to the impact criteria for the Detailed Vibration Analysis,
while deferring the selection of specific vibration control measures until the
completion of detailed studies in the engineering phase. When work is
conducted after FTA signs its final decision document (i.e., ROD, combined
FEIS/ROD, or FONSI), additional documentation, such as a reevaluation of the
previous decision, may be necessary. FTA recommends contacting the FTA
Regional office directly in these situations.
FEDERAL TRANSIT ADMINISTRATION 189
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
1d. Describe mitigation measures in the decision document – After the
decision document is approved, incorporate the mitigation measures by
reference in the actual grant agreements signed by FTA and the project sponsor.
The mitigation measures then become contractual conditions that must be
adhered to by the project sponsor.
It is typically appropriate to include the following noise and vibration
information in the environmental document, as described in Section 8.1:
The existing conditions (affected environment)
The direct impacts from operation (environmental consequences)
The construction impacts (environmental consequences)
Step 2: Organize information in the Environmental
Document
Include information in the following sections of the environmental document separating
out the noise and vibration information.
2a. Existing Conditions (Affected Environment) – Describe the existing
conditions (conditions without the project) in terms of the existing noise
and vibration conditions in this section of the document. The primary
function of this section is to establish the focus and baseline conditions for
the discussion of environmental impacts. Include the following basic
information and separate the noise and vibration sections.
Description of noise/vibration metrics, effects and typical level
s
–
Inc
lude a targeted summary of relevant information from Section 3
of
this manual. This will serve as background for the discussions of
nois
e/vibration levels and characteristics that will follow in lat
er
s
ections. Provide illustrative material to convey typical levels to t
he
publi
c
.
I
nventory of noise/vibration-sensitive sites – Describe t
he
a
pproach for identifying noise- and vibration-sensitive sites as well as t
he
identified
sites and site descriptions. Use sufficient detail to demonstrat
e
c
ompleteness. Document these results on a
map.
N
oise/vibration measurements – Document the basis for select
ing
measurement sites, including tables of sites coordinated with maps
s
howing locations of sites. Summarize the measurement approach a
nd
include the justification for the measurement procedures used.
P
resent measurement data in well-organized tables and figures with
a
summary and interpretation of measured data. Measurements are often
inc
luded in the table of measurement sites described in the prev
ious
pa
ragraph. In some cases, measurements may be supplemented
or
r
eplaced by collected data relevant to the noise and vibrat
ion
c
haracteristics of the area. For example, soil information for estimat
ing
g
round-borne vibration propagation characteristics may be availa
ble
fr
om other projects in the area
.
FEDERAL TRANSIT ADMINISTRATION 190
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
A summary and interpretation of how the collected data define the project
setting is fundamental to this section.
2b. Direct Impacts – Include the following in the discussion on direct impacts
due to project operation:
Overview of approach – Provide a targeted summary of relevant
information on the assessment procedure for determining
noise/vibration impacts as a framework for the following sections.
Estimated noise/vibration levels – Provide a general description of
prediction models used to estimate project noise/vibration levels.
Describe any distinguishing features unique to the project, such as
source levels associated with various technologies.
Describe the results of the predictions in general terms first, followed
by a detailed accounting of predicted noise levels. Supplement this
information with tables and illustrate by contours, cross-sections, or
shaded mapping. If contours are included in a technical report, it is not
necessary to repeat them in this section.
Criteria for noise/vibration impact – Describe the impact criteria
for the project in detail and reference the appropriate section in this
manual. Include tables listing the criteria levels or the figures included in
this manual.
Noise/vibration impact assessment – Present the impact
assessment in its own section or combined with the section above.
Describe the locations, as identified in the screening procedure, where
noise/vibration impact is expected to occur without implementation of
mitigation measures, based on the screening results, predicted future
levels, existing levels, and application of the impact criteria.
Include inventory tables of impacted noise- and vibration-sensitive sites
to quantify the impacts for all noise/vibration-sensitive sites included in
the Affected Environment (Existing Conditions) as described in the
Existing Conditions section above.
Noise/vibration mitigation measures – Perhaps the greatest
difference between the technical report and the environmental
document is with mitigation. The technical report discusses mitigation
options and recommendations, while the environmental document
provides the vehicle for reaching decisions on appropriate mitigation
measures.
Begin this section with a summary of the noise/vibration mitigation
measures considered for the impacted locations. Describe the specific
measures selected for implementation in detail. Also, include any
FEDERAL TRANSIT ADMINISTRATION 191
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
applicable, specific noise or vibration policies the project sponsor may
have in place.
In cases where it is not possible to commit to a specific mitigation
measure in the final environmental document, it may be possible to
commit to a certain noise/vibration level. For example, the
environmental document could include a commitment to meet or
exceed the impact criteria specified in Sections 4.1 and 6.2.
Unavoidable adverse environmental effects – If it is projected
that adverse noise/vibration impacts will result after all reasonable
abatement measures have been incorporated, identify these impacts in
this section.
2c. Construction Impacts – Discuss construction impacts in the
environmental document’s section on construction impacts, if present.
If, because of the scale of the project, the environmental document does
not have a separate construction impacts section, then the construction
impacts should be discussed with the rest of the resource impacts.
When a special section on construction noise/vibration impacts is
included in the document, it should be organized according to the
comprehensive outline on long-term impacts described above. For
projects with relatively minor effects, include a brief summary of impact.
8.2 Technical Report on Noise and Vibration
The technical report is intended to present complete technical data and
descriptions in a manner that can be understood by the general public, but is
more technical than the information found in the environmental document. All
necessary background information should be present in the technical report,
including tables, maps, charts, drawings, and references that may be too detailed
for the environmental document, but which are important in helping to draw
conclusions about the project's noise and vibration impacts and mitigation
options.
Include the following major subject headings and key information described
below. If both noise and vibration have been assessed, include separate sections
for noise and vibration with subsections for key information as described below.
Additional details on documentation requirements for the technical report of
non-standard procedures and methodologies are included in Appendix G.
Overview – Include a brief description of the project and an overview
of the noise/vibration concerns to highlight initial considerations in
framing the scope of the study.
Inventory of Noise/Vibration-Sensitive Sites – Describe the
approach for identifying noise- and vibration-sensitive sites as well as the
identified sites and site descriptions. Use sufficient detail to demonstrate
completeness. Document results on a map.
FEDERAL TRANSIT ADMINISTRATION 192
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Measurements of Existing Noise/Vibration Conditions
Document the basis for selecting measurement sites, including
tables of sites coordinated with maps showing locations of sites.
Summarize the measurement approach with justification for the
measurement procedures used.
If the measurement data are used to estimate existing conditions at
other locations, include the rationale and the method of estimation.
Describe measurement procedures in detail.
Include tables of measurement instruments documenting
manufacturer, type, serial number, and date of most recent
calibration by authorized testing laboratory. Document
measurement periods, including the time of day and length of time
at each site to demonstrate adequate representation of ambient
conditions.
Present measurement data in well-organized tables and figures with
a summary and interpretation of measured data.
Additional Measurements Related to the Project – Include
detailed description of measurements and results for projects that
require specialized measurements at noise- and vibration-sensitive sites.
Examples include:
Outdoor-to-indoor noise level reduction of homes
Transmission of vibration into concert halls and recording studios
Special source-level characterization
Predictions of Noise/Vibration from the Project
Describe the prediction model used to estimate future project
conditions and specific data used as input to the models. Reference
the appropriate section in this manual. Document any change or
extension to the models recommended in this manual, so that the
validity of the adjustments can be confirmed. See Appendix G for
more information.
Describe in detail the modeled scenarios and why the scenarios
were chosen.
Tabulate computed levels and illustrate by contours, cross-sections,
or shaded mapping. Illustrate noise/vibration impacts with base maps
at a scale with enough detail to provide reference for the location.
Noise/Vibration Criteria
Describe the impact criteria for the project in detail and reference
the appropriate section in this manual. Include tables specifying the
criteria levels or the figures included in this manual.
If construction noise and/or vibration assessments were conducted,
include the construction criteria in a separate section with the
construction assessment details. See below for more information.
FEDERAL TRANSIT ADMINISTRATION 193
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Noise/Vibration Impact Assessment
Describe the impact assessment according to the appropriate noise
a
nd/or vibration impact assessment sections in this manua
l.
If
an alternatives analysis was conducted, present a resulting impac
t
inv
entory for each alternative mode or alignment in a format tha
t
a
llows comparison among alternatives
.
T
abulate the inventory according to the different types of affect
ed
nois
e- and vibration-sensitive sites. Present the results of t
he
a
ssessment both before and after mitigati
on.
Noise/Vibration Mitigation
Begi
n this section with a summary of all treatments consider
ed,
including those not carried to final consideration.
Cons
ider final candidate mitigation treatments separately a
nd
provide a description of the features of the treatment, including
costs, expected benefit in reducing impacts, locations where the
benefi
t would be realized, and a discussion of the practicality
of
a
lternative treatments
.
Inc
lude enough noise and vibration impact information to allow t
he
pr
oject sponsor and FTA to reach decisions on mitigation prior t
o
is
suance of an environmental decision document
.
Co
nstruction Noise/Vibration Impact
s
Des
cribe criteria adopted for construction noise or vibration
if
c
onstruction noise and/or vibration assessments were conduct
ed.
Des
cribe the method used for predicting construction noise
or
vibration and include inputs to the models such as equipment roster
by
construction phase, equipment source levels, assumed usag
e
fa
ctors, and other assumed site characteristics
.
Pr
esent predicted levels for noise- and vibration-sensitive sites an
d
identify sh
ort-term impacts
.
In
cases where construction impacts are identified, discuss feasibl
e
a
batement methods using enough detail to allow construct
ion
c
ontract documents to include mitigation measures
.
R
eferences – Provide references for all criteria, approaches, and dat
a
used in the analyses, as well as other reports related to the project that
may
be relied on for information, e.g., geotechnical reports
.
FEDERAL TRANSIT ADMINISTRATION 194
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Appendix A: Glossary of Terms
Terminology used through the manual is defined in this appendix.
(49)(
72
)
A-weighting
A standardized filter used to alter the sensitivity of a sound level meter with respect
to frequency so that the instrument is less sensitive at low and high frequencies
where the human ear is less sensitive. Abbreviated as dBA.
Absolute Noise
Impact
Noise that interferes with activities independent of existing noise levels and is
expressed as a fixed level threshold.
Accelerometer
A transducer that converts vibratory motion to an electrical signal proportional to
the acceleration of that motion.
Ambient
The pre-project background noise or vibration level, which is often used
interchangeably with “existing noise” in this manual.
Amplitude
Difference between the extremes of an oscillating signal.
Alignment
The horizontal location of a railroad or transit system as described by curved and
tangent track.
At-grade
Tracks on the ground surface.
Automated Guideway
Transit (AGT)
Guided steel-wheel or rubber-tired transit passenger vehicles operating singly or in
multi-car trains with a fully automated system on fixed-guideways along an exclusive
ROW. AGT includes personal rapid transit, group rapid transit, and automated
people mover systems.
Auxiliaries
The term applied to a number of separately driven machines, operated by power
from the main engine or electric generation. They include the air compressor,
radiator fan, traction motor blower, and air conditioning equipment.
Ballast mat
A 2- to 3-inch-thick elastomer mat placed under the normal track ballast on top of a
rigid slab or packed sub-grade.
Ballast
Granular material placed on the trackbed for the purpose of holding the track in line
and at surface.
Bus Rapid Transit
(BRT)
A type of limited-stop bus operation that relies on technology to help speed up the
service. Buses can operate on exclusive transitways, high-occupancy-vehicle lanes,
expressways, or ordinary streets.
Catenary
On electric railroad and LRT systems, the term describing the overhead conductor
that is contacted by the pantograph or trolley, and its support structure.
Commuter rail
Conventional passenger railroad serving areas surrounding an urban center. Most
commuter railroads utilize locomotive-hauled coaches, often in push-pull
configuration.
Consist
The total number and type of cars, locomotives, or transit vehicles in a trainset.
Continuous welded
rail
A number of rails welded together to form unbroken lengths of track without gaps
or joints.
Corrugated rail
A rough condition of alternating ridges and grooves which develops on the rail head
in service.
Crest factor
The ratio of peak particle velocity to maximum RMS amplitude in an oscillating signal.
Criteria
Plural form of “criterion,” the relationship between a measure of exposure (e.g.,
sound or vibration level) and its corresponding effect.
Cross tie
The transverse member of the track structure to which the rails are spiked or
otherwise fastened to provide proper gage and to cushion, distribute, and transmit
the stresses of traffic through the ballast to the trackbed.
Crossover
Two turnouts with the track between the frogs arranged to form a continuous
passage between two nearby and generally parallel tracks.
Cumulative
The summation of individual sounds into a single total value related to the effect over
time.
Cut
A terrain feature typically created to allow for a trackbed to be at a lower level than
the surrounding ground.
FEDERAL TRANSIT ADMINISTRATION 195
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
dB
See Decibel.
dBA
See A-weighting.
Decibel
The standard unit of measurement for sound pressure level and vibration level.
Technically, a decibel is the unit of level which denotes the ratio between two
quantities that are proportional to power; the number of decibels is 10 times the
logarithm of this ratio. Abbreviated as dB.
DMU
Diesel-powered multiple unit. See Multiple Unit.
DNL
See L
dn
.
Electrification
A term used to describe the installation of overhead wire or third rail power
distribution facilities to enable operation of trains.
Embankment
A bank of earth, rock, or other material constructed above the natural ground
surface.
Equivalent level
The level of a steady sound, which, in a stated time period and at a stated location,
has the same sound energy as the time-varying sound. Also, written as L
eq
.
Event
A passby of a vehicle (e.g., train, bus, or car) of any size consist.
Ferry boat
A transit mode comprised of vessels to carry passengers and/or vehicles over a body
of water.
Fixed-guideway
A public transportation facility with a separate ROW for the exclusive use of public
transportation and other high-occupancy vehicles.
Flange
The vertical projection along the inner rim of a wheel that serves, together with the
corresponding projection of the mating wheel of a wheel set, to keep the wheel set
on the track.
Floating slab
A special track support system for vibration isolation, consisting of concrete slabs
supported on resilient elements, usually rubber or similar elastomer.
Force density
Force density is the force per root distance along the track in lb/ft
1/2
. The force
density level is the level in decibels of the force density relative to 1 lb/ft
1/2
and
describes the vehicle force that excites the soil/rock surrounding the transit
structure.
Frequency
The number of times that a periodically occurring quantity repeats itself in a specified
period. With reference to noise and vibration signals, the number of cycles per
second.
Frequency spectrum
Distribution of frequency components of a noise or vibration signal.
Frog
A track structure used at the intersection of two running rails to provide support for
wheels and passageways for their flanges, thus permitting wheels on either rail to
cross the other.
Gage (of track)
The distance between the rails on a track.
Grade crossing
The point where a rail line and a motor vehicle road intersect at the same vertical
elevation.
Guideway
Supporting structure to form a track for rolling or magnetically-levitated vehicles.
Head-End Power
(HEP)
A system of furnishing electric power for a complete railway train from a single
generating plant in the locomotive.
Heavy rail
See Rail Rapid Transit.
Hertz (Hz)
The unit of acoustic or vibration frequency representing cycles per second.
Hourly average sound
level
The time-averaged A-weighted sound level, over a 1-hour period, usually calculated
between integral hours. Abbreviated as L
(1h).
Hybrid Bus
A rubber-tired vehicle that features a hybrid diesel-electric propulsion system. A
diesel engine runs an electric generator that powers the entire vehicle including
electric drive motors that deliver power to the wheels.
Idle
The speed at which an engine runs when it is not under load.
Intermediate Capacity
Transit (ICT)
A transit system with less capacity than rail rapid transit (RRT), but more capacity
than typical bus operations. Examples of ICT include bus rapid transit (BRT),
automated guideway transit (AGT), monorails, and trolleys.
Intermodal facility
Junction of two or more modes of transportation where transfers may occur.
Jointed rail
A system of joining rails with steel members designed to unite the abutting ends of
contiguous rails.
FEDERAL TRANSIT ADMINISTRATION 196
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
L
(1h)
See Hourly Average Sound Level.
L
dn
Day-Night Sound Level. The sound exposure level for a 24-hour day calculated by
adding the sound exposure level obtained during the daytime (7 a.m. to 10 p.m.) to
10 times the sound exposure level obtained during the nighttime (10 p.m. to 7 a.m.).
This unit is used throughout the United States for environmental impact assessment.
Also, written as DNL.
L
eq(1hr)
Equivalent Sound Level. The metric for cumulative noise exposure over a specific
time interval is the equivalent sound level
Light Rail Transit
(LRT)
A mode of public transit with tracked vehicles in multiple units operating in mixed
traffic conditions on streets as well as sections of exclusive ROW. Vehicles are
generally powered by electricity from overhead lines.
Locomotive
A self-propelled, non-revenue rail vehicle designed to convert electrical or
mechanical energy into tractive effort to haul railway cars. See also Power Unit.
Main line
The principal line or lines of a railway.
Maglev
Magnetically-levitated vehicle; a vehicle or train of vehicles with guidance and
propulsion provided by magnetic forces. Support can be provided by either an
electrodynamic system wherein a moving vehicle is lifted by magnetic forces induced
in the guideway or an electromagnetic system wherein the magnetic lifting forces are
actively energized in the guideway.
Maximum sound level
The highest exponential-time-average sound level, in decibels, that occurs during a
stated time period. Abbreviated as L
max
. The standardized time periods are 1 second
for L
max
, slow, and 0.125 second for L
max
, fast.
Metric
Measurement value or a quantitative descriptor used to identify a specific measure of
sound level.
Monorail
Guided transit vehicles operating on or suspended from a single rail, beam, or tube.
Multimodal Project
In this manual, the term multimodal project is used to describe a project that
includes changes to both transit and highway components in segments of the project.
Multiple Unit (MU)
A term referring to the practice of coupling two or more diesel-powered or electric-
powered passenger cars together with provision for controlling the traction motors
on all units from a single controller.
Noise
Any disagreeable or undesired sound or other audible disturbance.
Octave band
A standardized division of a frequency spectrum in which the interval between two
divisions is a frequency ratio of 2.
One-third octave
band
A standardized division of a frequency spectrum in which the octave bands are
divided into thirds for more detailed information. The interval between center
frequencies is a ratio of 1.25.
Pantograph
A device for collecting current from an overhead conductor (catenary), consisting of
a jointed frame held up by springs or compressed air and having a current collector
at the top.
Park-and-ride facility
A parking garage and/or lot used for parking passengers’ automobiles while they use
transit agency facilities and vehicles.
Peak factor
See Crest factor.
Plan-and-profile
Mapping used by transportation planners that shows two-dimensional plan views (x-
and y- axes) on the same page as two-dimensional profiles (x- and z-axes) of a road
or track.
Peak Particle Velocity
(PPV)
The peak signal value of an oscillating vibration velocity waveform. Usually expressed
in inches/second in the United States.
Peak-to-Peak (P-P)
Value
Of an oscillating quantity, the algebraic difference between the extreme values of the
quantity.
Power unit
A self-propelled vehicle, running on rails and having one or more electric motors that
drive the wheels and thereby propel the locomotive and train. The motors obtain
electrical energy either from a rail laid near, but insulated from, the track rails, or
from a wire suspended above the track. Contact with the overhead wire is made by a
pantograph mounted on top of the unit.
Project segment
Portions of a project with similar characteristics.
FEDERAL TRANSIT ADMINISTRATION 197
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Pure tone
Sound of a single frequency.
Radius of curvature
A measure of the severity of a curve in a track structure based on the length of the
radius of a circle that would be formed if the curve were continued.
Rail
A rolled steel shape, commonly a T-section, designed to be laid end to end in two
parallel lines on cross ties or other suitable supports to form a track for railway
rolling stock.
Rail Rapid Transit
(RRT)
Often called “Heavy Rail Transit.” A mode of public transit with tracked vehicles in
multiple units operating in exclusive rights-of-way. Trains are generally powered by
electricity from a third rail alongside the track.
Receiver
A stationary far-field position at which noise or vibration levels are specified.
Relative Noise Impact
Noise increase above existing levels.
Resonance frequency
The phenomenon that occurs in a structure under conditions of forced vibration
such that any change in frequency of excitation results in a decrease in response.
Right-of-Way
Abbreviated as ROW. Lands or rights used or held for railroad or transit operation.
Root Mean Square
(rms)
The square root of the mean-square value of an oscillating waveform, where the
mean-square value is obtained by squaring the value of amplitudes at each instant of
time and then averaging these values over the sample time.
RMS Velocity Level
(LV)
See Vibration Velocity Level.
SEL
See Sound Exposure Level.
Sound Exposure Level
The level of sound accumulated over a given time interval or event. Technically, the
sound exposure level is the level of the time-integrated mean square A-weighted
sound for a stated time interval or event, with a reference time of one second.
Abbreviated as SEL.
Sound
A physical disturbance in a medium that is capable of being detected by the human
ear.
Spectrum
See Frequency Spectrum.
Sub-ballast
Any material of a superior character, which is spread on the finished subgrade of the
roadbed and below the top-ballast, to provide better drainage, prevent upheaval by
frost, and better distribute the load over the roadbed.
Subgrade
The finished surface of the roadbed below the ballast and track.
Suburban bus
A bus similar to an intercity bus with high-backed seats but no luggage compartment,
often used in express mode to city centers from suburban locations.
Switch
A track structure used to divert rolling stock from one track to another.
Tangent track
Track without curvature.
Track
An assembly of rail, ties, and fastenings over which cars, locomotives, and trains are
moved.
Traction motor
A specially designed direct current series-wound motor mounted on the trucks of
locomotives and self-propelled cars to drive the axles.
Trainset
A group of coupled cars including at least one power unit.
Transducer
Device designed to receive an input signal of a given kind (motion, pressure, heat,
etc.) and to provide an output signal of a different kind (electrical voltage, amperage,
etc.) in such a manner that desired characteristics of the input signal appear in the
output signal for measurement purposes.
Transfer mobility
Transfer mobility is the complex velocity response produced by a point force as a
function of frequency and represents the relationship between a vibration source that
excites the ground and the resulting vibration of the ground surface.
Transit center
A fixed location where passengers interchange from one route or vehicle to another.
Trolley bus
A rubber-tired, electrically-powered bus operating on city streets drawing power
from overhead lines.
Truck
The complete assembly of parts including wheels, axles, bearings, side frames, bolster,
brake rigging, springs, and all associated connecting components, the function of
which is to provide support, mobility, and guidance to a railroad car or locomotive.
Trunk line
See Mainline. The mainline of a commuter railroad where the branch line traffic is
combined.
FEDERAL TRANSIT ADMINISTRATION 198
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Turnout
An arrangement of a switch and a frog with closure rails, by means of which rolling
stock may be diverted from one track to another.
VdB
See Vibration Velocity Level.
Vibration Velocity
Level (LV)
Ten times the common logarithm of the ratio of the square of the amplitude of the
RMS vibration velocity to the square of the amplitude of the reference RMS vibration
velocity. The reference velocity in the United States is one micro-inch per second.
Abbreviated as VdB.
Vibration
An oscillation wherein the quantity is a parameter that defines the motion of a
mechanical system.
Wheel flat
A localized flat area on a steel wheel of a rail vehicle, usually caused by skidding on
steel rails, causing a discontinuity in the wheel radius.
Wheel squeal
The noise produced by wheel-rail interaction, particularly on curves where the radius
of curvature is smaller than allowed by the separation of the axles in a wheel set.
Additional, relevant acoustic terminology and formulas are defined in ANSI S1.1-1994 (49).
FEDERAL TRANSIT ADMINISTRATION 199
where:
= sound pressure
= individual sound pressure
= number of samples
= index of summation
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Appendix B: Fundamentals of Noise
Noise is generally considered to be unwanted sound. Sound is what we hear when our ears are exposed
to small pressure fluctuations in the air. There are many ways in which pressure fluctuations are
generated, but typically they are caused by vibrating movement of a solid object. This manual uses the
terms noise and sound interchangeably because there is no physical difference between them. Noise can
be described in terms of three variables: amplitude (loud or soft); frequency (pitch); and time pattern
(variability).
B.1 Amplitude
The loudness of a sound is described by the sound wave’s amplitude of pressure fluctuations above and
below atmospheric pressure. Pressure is measured in Pascals. The mean value of the positive and
negative pressure fluctuations is the static atmospheric pressure and is not a useful metric of sound.
However, the effective magnitude of the sound pressure in a sound wave can be expressed by the rms
of the oscillating pressure. See Figure B-1 for an illustration of the rms pressure.
The rms pressure is calculated according to Eq. B-1. The values of sound pressure are squared and time-
averaged to smooth out variations. The rms pressure is the square root of this time-averaged value.
Eq. B-1
Figure B-1 RMS Pressure Illustration
Most humans with typical or average hearing can perceive sounds ranging from approximately 20
microPascals to 20 million microPascals or more. Because of the difficulty in dealing with such an
extreme range of numbers, acousticians use a logarithmic scale to describe sound levels. Acousticians
use a compressed scale based on logarithms of the ratios of the sound energy contained in the wave
related to the square of sound pressures instead of the sound pressures themselves, resulting in the
“sound pressure level” in decibels (dB). The ‘B’ in dB is always capitalized because the unit is named
after Alexander Graham Bell, a leading 19th century innovator in communication.
FEDERAL TRANSIT ADMINISTRATION 200
= sound pressure level, dB
= individual source RMS sound pressures to add
= 20 microPascals
where
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Sound pressure level (L
p
) is defined as:
Eq. B-2
where
= sound pressure level, dB
= RMS sound pressure
= 20 microPascals
Inserting the range of sound pressure values mentioned above into Eq. B-2 results in a typical quietest
sound at 20 microPascals at 0 dB. A typical loudest sound of 20 million microPascals is 120 dB.
B.1.1 Decibel Addition
The combination of two or more sound pressure levels at a single location requires decibel addition,
which is the addition of logarithmic quantities of sound energy (P
2
rms
).
To add sound energy from multiple, unique sources, add the sound energy as shown Eq. B-3.
Eq. B-3
A doubling of identical sound sources results in a 3-dB increase, as shown mathematically below.
To add decibel levels (instead of sound energy) use the following equation:
where
FEDERAL TRANSIT ADMINISTRATION 201
where
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
= sound pressure level, dB
= number of samples
= index of summation
= individual sound pressure levels, dB
= sound pressure level, dB
= individual source sound pressure levels to add
The equation above can be rewritten as follows:
Eq. B-4
= individual source sound pressure levels to add
Decibel addition can be quickly approximated using Figure B-2.
Figure B-2 Graph for Approximate Decibel Addition
FEDERAL TRANSIT ADMINISTRATION 202
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Example B-1 Decibel Addition – Identical Buses
Decibel Addition
What is the combined sound pressure level of two identical buses if the noise from one bus resulted in a sound
pressure level of 70 dB?
Since a doubling of identical sound sources results in a 3-dB increase:
Example B-2 Decibel Addition – Two Sources
Decibel Addition
What is the combined sound pressure level of 64 dB and 60 dB?
Using Eq. B-4:
Using Figure B-2:
The x-axis values represent the difference between the two sound levels, 64 and 60 dB. The difference between
the sound levels in this example is 4. The point on the curve corresponding to 4 on the x-axis is 1.5. The y-axis
values represent the increment that is added to the higher level.
B.1.2 Frequency
Sound is a fluctuation of air pressure. The number of times the fluctuation occurs in one second is called
its frequency. In acoustics, frequency is quantified in cycles per second, or Hertz (Hz). The hearing for a
typical human covers the frequency range from 20 Hz to 20,000 Hz.
Some sounds, like whistles, are associated with a single frequency; this type of sound is called a pure
tone. However, most often, noise is made up of many frequencies, called a spectrum. Analyzing a noise
spectrum allows for identification of dominant frequency ranges and can assist in identifying noise
sources. Often a frequency spectrum is divided into standardized frequency bands for analysis. Most
commonly, the frequency bands for transit analyses are octave bands (where the interval between two
divisions is a frequency ratio of 2) and one-third octave bands (where the interval between center
frequencies is a ratio of 1.25).
(
73
)
If the spectrum associated with a transit noise source is dominated by many low-frequency components,
the noise will have a characteristic like the rumble of thunder; this is often associated with noise from a
subway. Mid-range frequencies are often associated with wheel/rail noise, and high frequencies may be
associated with wheel squeal due to sharp curves on a track.
The spectrum in Figure B-3 illustrates the full range of acoustical frequencies that can occur near a
transit system. In this example, the noise spectrum was measured near a train on an elevated steel
structure with a sharp curve.
FEDERAL TRANSIT ADMINISTRATION 203
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Figure B-3 Noise Spectrum of Transit Train on Curve and Elevated Structure
The human auditory system does not respond equally to all frequencies of sound. For sounds normally
heard in our environment, low frequencies below 250 Hz and frequencies above 10,000 Hz are generally
considered less audible than the frequencies in between. This is because our ears are less sensitive in
those areas. To better represent human hearing, frequency response functions were developed to
characterize the way people respond to different frequencies. These are referred to as A-, B-, and C-
weighted curves and represent human auditory response to normal, very loud, and extremely loud
sound levels, respectively. Environmental noise is generally considered to be in the normal sound level
range; and, therefore, the A-weighted sound level is considered best to represent the human response.
The A-weighting curve is shown in Figure B-4. This curve illustrates that sounds at 50 Hz would have to
be amplified by 30 dB to be perceived as loud as a sound at 1000 Hz at normal sound levels.
FEDERAL TRANSIT ADMINISTRATION 204
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Figure B-4 A-Weighting Curve
Low frequencies have longer wavelengths of sound (cycles are less frequent) and, conversely, high
frequencies have shorter wavelengths (cycles are more frequent). The size of the wavelength in feet is
dependent on frequency and speed of sound as follows:
Eq. B-5
where
= frequency in cycles per second, Hz
= wavelength, ft
= speed of sound, ft/sec
The speed of sound in air varies with temperature; but at standard conditions, it is approximately 1000
ft per second. Therefore, at standard conditions, a frequency of 1000 Hz has a wavelength of 1 foot and
a frequency of 50 Hz has a wavelength of 20 ft. The scale of these waves explains, in part, the reason
humans perceive sounds of 1000 Hz better than those of 50 Hz. A wavelength of 1 foot is similar to the
size of a person’s head; whereas, a wavelength of 20 ft is similar to dimensions associated with a house,
which is why low-frequency sounds (such as those from an idling locomotive) are sometimes not
attenuated by walls and windows of a home. These sounds transmit indoors with relatively little
reduction in strength.
B.1.3 Time Pattern
The third important characteristic of noise is its variation in time. Environmental noise is considered to
be a combination of all outdoor noise sources. When combined, sources such as distant traffic, wind in
trees, and distant industrial or farming activities often create a low-level background noise in which no
particular individual source is identifiable. Background noise is often relatively constant from moment to
moment, but varies slowly over time as natural forces change or as human activity follows its daily cycle.
In addition to this low-level, slowly varying background noise, a succession of identifiable noisy events of
relatively brief duration may be added. These events may include single-vehicle passbys, aircraft flyovers,
FEDERAL TRANSIT ADMINISTRATION 205
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
screeching of brakes, and other short-term events, which all cause the noise level to substantially
fluctuate from moment to moment.
It is possible to describe these fluctuating noises in the environment using single-number metrics to
allow for manageable measurements, computations, and impact assessment. The search for adequate
single-number noise metrics has encompassed hundreds of attitudinal surveys and laboratory
experiments in addition to decades of practical experience with many alternative metrics.
B.1.4 Noise Metrics
The noise metrics referred to in this manual are described in the sections below.
B.1.4.1 A-weighted Sound Level: The Basic Noise Unit
The basic noise unit for transit noise is the A-weighted sound level and is described in ANSI S1.1-1994
(49). It describes the noise level at the receiver at any moment in time and can be read directly from
noise-monitoring equipment when frequency weighting is set to A-weighting. Figure B-5 shows examples
of typical A-weighted sound levels for both transit and non-transit sources, ranging from approximately
30 dBA (very quiet) to 90 dBA (very loud).
The unit dBA denotes the decibel level is A-weighted. The letter "A" indicates that the sound has been
filtered to reduce the strength of very low and very high-frequency sounds to emulate the human
response to sound levels as described in Appendix B.1.2. This allows for events that are out of the range
of human hearing, such as high-frequency dog whistles and low-frequency seismic disturbances, to be
filtered out. On average, each A-weighted sound level increase of 10 dB corresponds to an approximate
doubling of subjective loudness.
A-weighted sound levels are adopted as the basic noise unit for transit noise impact assessments
because they:
Ca
n be measured easily
,
A
pproximate the human ear's sensitivity to sounds of different frequencies
,
Match
attitudinal-survey tests of annoyance better than other basic units
,
Ha
ve been in use since the early 1930s, a
nd
A
re endorsed as the proper basic unit for environmental noise by most agencies concerned wit
h
c
ommunity noise throughout the worl
d.
FEDERAL TRANSIT ADMINISTRATION 206
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Figure B-5 Typical A-weighted Sound Levels
B.1.4.2 Maximum Sound Level (L
max
) During a Single Noise Event
As a transit vehicle approaches, passes by, and then recedes into the distance, the A-weighted sound
level rises, reaches a maximum, and then fades into the background noise. The maximum A-weighted
sound level reached during this passby is called the maximum sound level,
(49)
abbreviated here as L
max
.
L
max
is illustrated in Figure B-6 where time is plotted horizontally, and A-weighted sound level is plotted
vertically.
Although
L
max
is commonly used in vehicle-noise specifications,
xvi
it is not used for transit environmental
noise impact assessment.
L
max
does not include the number and duration of transit events, which are
important for assessing people's reactions to noise. It also cannot be normalized to a one-hour or
24-hour cumulative measure of impact, and therefore, is not conducive to comparison among different
t
ransportation modes. For example, cumulative noise metrics commonly used in highway nois
e
a
ssessments are
L
eq(1hr)
and L
10
, the noise level exceeded for 10 percent of the peak hour.
xvi
For noise compliance tests of transient sources, such as moving transit vehicles under controlled conditions with smooth
wheel and rail conditions, L
max
is typically measured with the sound level meter's time weighting set to "fast." However, for
tests of continuous or stationary transit sources, it is usually more appropriate to use the "slow" setting. When set to "slow,"
sound level meters ignore some of the very-transient fluctuations, which are negligible when assessing the overall noise level.
FEDERAL TRANSIT ADMINISTRATION 207
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Figure B-6 Typical Transit-Vehicle Passby
B.1.4.3 Sound Exposure Level (SEL): Exposure from a Single
Noise Event
Sound exposure level, abbreviated here as SEL, is the cumulative noise exposure from a single noise
event, normalized to one second (49). SEL contains the same overall sound energy as the actual varying
sound energy during the event. It is the primary metric for the measurement of transit vehicle noise
emissions and an intermediate metric in the measurement and calculation of both
L
eq(1hr)
and L
dn
. The SEL
metric is A-weighted and is expressed in the unit dBA.
This concept is illustrated in Figure B-6 and Figure B-7 where the shaded regions are the sound
exposure during and event. The example in Figure B-6 is a transit-vehicle passby and Figure B-7 is an
example of a fixed-transit facility as a transit bus is started, warmed up, and then driven away. For this
event, the noise exposure is large due to duration of the event.
SEL is an A-weighted cumulative measure that is referenced to one second. Louder events have greater
SELs than quieter events, and events of longer duration have greater SELs than shorter events. This is
generally consistent with community response to noise. Noise events of longer duration are considered
more disruptive than events of shorter duration with equal maximum A-weighted sound levels.
Figure B-7 Typical Fixed-Facility Noise Event
FEDERAL TRANSIT ADMINISTRATION 208
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Conceptually, the sound exposure level can be expressed as:
Mathematically, the sound exposure level is computed as follows:
Eq. B-6
where
SEL
= Sound exposure level, dBA
= number of samples
= index of summation
= individual A-weighted sound level, dBA
The events shown in Figure B-6 and Figure B-7 are compared graphically in Figure B-8 using a
logarithmic vertical scale. The shaded zones in these figures indicate noise exposure over time. The
actual event shows the noise exposure over the time of the event, and the equivalent SEL shows the
total noise exposure normalized to one second. Note that events 1 and 2 in Figure B-8 have different
time periods and noise levels throughout the event, but the same resulting SEL.
SEL is used in transit noise analyses because it:
1. Accounts for both the duration and amplitude of an event
,
2. A
llows a uniform assessment method for both transit-vehicle passbys and fixed-facility nois
e
ev
ents, a
nd
3. Ca
n be used to calculate the one-hour and 24-hour cumulative metrics for comparison acr
oss
differ
ent transportation modes
.
FEDERAL TRANSIT ADMINISTRATION 209
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Figure B-8 An Energy View of Noise Events
B.1.4.4 Equivalent Sound Level (L
eq(t)
)
The metric for cumulative noise exposure over a specific time interval is the equivalent sound level (49).
It is a single decibel value that accounts for total sound energy from all sound levels over a specified time
interval (or time period). The time period associated with the equivalent sound level metric can vary for
different types of analyses. This metric is abbreviated as
L
eq(t)
, where “t” is the duration of the time
period.
L
eq(t)
represents a hypothetical constant sound level and contains the same overall sound energy
as the actual varying sound energy during the time period “t”. For most transit noise analyses, an A-
weighted, hourly equivalent sound level is used, abbreviated here as
L
eq(1hr)
. L
eq(1hr)
is expressed in the unit,
dBA.
Figure B-9 shows examples of typical unmitigated hourly
L
eq(1hr)
's, both for transit and non-transit sources
ranging from 40 (quiet) to 80 dB (loud). Note that these
L
eq(1hr)
's depend upon both the number of
events during the hour as well as each event's duration, which is affected by vehicle speed. For example,
doubling the number of events during the hour will increase the
L
eq(1hr)
by 3 decibels, as will doubling the
duration of each individual event.
FEDERAL TRANSIT ADMINISTRATION 210
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Figure B-9 Typical Hourly L
eq(1hr)
's
An example of sound levels over time for a single noise event such as a train passing on nearby tracks is
illustrated in the top frame of Figure B-10. As the train approaches, passes by, and then recedes into the
distance, the A-weighted sound level rises, reaches a maximum, and then fades into the background
noise. The equivalent sound level is shown for three different time periods Figure B-10. The area under
the curve in this top frame is the noise that reaches the receiver (noise exposure) over this five-minute
period. The center frame of the figure shows sound levels over the one-hour period, including the five-
minute period from the top frame. The area under the curve represents the noise exposure for one
hour. The bottom frame shows sound levels over a full 24-hour period and is discussed in Appendix
B.1.4.5.
FEDERAL TRANSIT ADMINISTRATION 211
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Figure B-10 Example A-weighted Sound Level Time Histories
Conceptually, the equivalent sound level can be expressed as:
FEDERAL TRANSIT ADMINISTRATION 212
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Mathematically, the equation is as follows:
where
L
eq(t)
= equivalent sound level of time period “t”, dBA
= time period, sec (3600 for an hourly L
eq(1hr)
)
= number of samples, sec (3600 for an hourly L
eq(1hr)
)
= index of summation
= individual A-weighted sound level, dBA
The equation above can be rewritten as follows for a one-hour time period:
Eq. B-7
where
35.6
= numerical adjustment for a time period of 1 hour (10log
10
(t))
The sound energy is totaled over a full hour (3600 seconds) and is accumulated for all noise events
during that hour. When computing the equivalent sound level for a time period other than one hour, T
is modified in the equation to the duration of the time period in seconds. The numerical adjustment
(35.6) accounts for time period of interest, in this case, one hour.
An alternate way for computing
L
eq(1hr)
for a series of transit-noise events using sound exposure levels can
be expressed conceptually as follows:
Mathematically, the equation is as follows:
Eq. B-8
where
L
eq(t)
= equivalent sound level of time period “t”, dBA
= time period, sec (3600 for an hourly L
eq(1hr)
)
= number of sample, sec (3600 for an hourly L
eq(1hr)
)
= index of summation
= individual sound exposure level, dBA
Hourly L
eq(1hr)
is adopted as the measure of cumulative noise impact for non-residential land uses (those
not involving sleep) because
L
eq(1hr)
:
Correlates well with speech interference in conversation and on the telephone – as well a
s
inter
ruption of TV, radio, and music enjoyment
;
Inc
reases with the duration of transit events
;
A
ccounts for the number of transit events over the hour, which is also important to people'
s
r
eactions; a
nd
FEDERAL TRANSIT ADMINISTRATION 213
TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
Is used by the Federal Highway Administration in assessing highway-traffic noise impact.(Thus,
this noise metric can be used for directly comparing and contrasting highway, transit, and
mult
imodal alternatives)
.
B.1.4.5 Day-Night Sound Level (L
dn
): 24-Hour Exposure from
All Events
The metric for cumulative 24-hour exposure is the Day-Night Sound Level,
(49)
abbreviated here as L
dn
.
It is a single, A-weighted decibel value that accounts for total sound energy from all sound sources over
24 hours and is expressed in the unit, dBA. Events between 10 p.m. and 7 a.m. are increased by 10 dB to
account for people’s greater nighttime sensitivity to noise.
Figure B-11 shows examples of typical L
dn
's, both for transit and non-transit sources, ranging from 50 to
80 dB, where 50 is considered a quiet 24-hour period and 80 a loud 24-hour period. Note that these
L
dn
's depend upon the number of events during day and night separately, including each event's duration,
which is affected by vehicle speed.
Figure B- 11 Typical L
dn
's
An example of sound level variation over 24 hours is visualized in the bottom frame of Figure B-10. The
area under the curve represents the receiver's noise exposure over the 24 hours. Note that some
vehicle passbys occur at night, when the background noise is typically lower and the 10 dB adjustment is
applied.
Conceptually, the day-night level can be expressed as:
FEDERAL TRANSIT ADMINISTRATION 214
Mathematically, the equation is as follows:
Eq. B-9
where
= cumulative 24-hour exposure (day-night sound level), dBA
= time period during the daytime, between 7 a.m. and 10 p.m. sec (54,000)
= number of samples during the daytime (54,000)
= index of summation
= time interval of measurements in seconds (1)
= individual A-weighted sound level during the daytime, dBA
= time period during the nighttime, between 10 p.m. and 7 p.m. sec (32,400)
= number of samples during the nighttime (32,400)
= index of summation
= time interval of measurements, sec (1)
= individual A-weighted sound level during the nighttime, dBA
= nighttime noise adjustment (10 dB)
The equation above can be rewritten as follows:
The sound energy is totaled over a full 24 hours, and the sound energy is accumulated from all noise
events
during that time period. The numerical adjustment (49.4) accounts for time period of interest, in
this case, 24 hours.
An alternative way of computing L
dn
from twenty-four hourly L
eq(1hr)
's can be expressed conceptually as
follows:
The equation above can be rewritten as:
The equation above can be reduced further and rewritten as:
Eq. B-10
FEDERAL TRANSIT ADMINISTRATION 215
L
dn
due to a series of transit-noise events can also be computed in terms of SEL. The equation below
assumes that transit noise dominates the 24-hour noise environment, where nighttime SELs are
increased by 10 dB before totaling:
Eq. B-11
L
dn
is adopted as the measure of cumulative noise impact for residential land uses (those involving sleep),
because it:
Correlates well with the results of attitudinal surveys of residential noise impact
Increases with the duration of transit events
Accounts for the number of transit events over the full twenty-four hours
Accounts for the increased sensitivity to noise at night, when most people are asleep
Allows composite measurements to capture all sources of community noise combined
Allow quantitative comparison of transit noise with other community noises
Is the designated metric of choice of other Federal agencies (e.g., HUD, FAA, and EPA) and has
wi
de international acceptanc
e
FEDERAL TRANSIT ADMINISTRATION 216
Appendix C: Background for Transit Noise Impact
Criteria
The noise criteria presented in Section 4.1 of this manual have been developed based on well-
documented criteria and research on human response to community noise. The primary goals in
developing the noise criteria were to ensure that the impact limits are firmly founded in scientific
studies, realistically based on noise levels associated with new transit projects, and represent a
reasonable balance between community benefit and project costs. This appendix provides background
information on the development of these criteria.
C.1 Relevant Literature
The following is an annotated list of the documents that are particularly relevant to the noise impact
criteria:
1. U.S. EPA’s "Levels Document”
(
74
)
This report identifies noise levels consistent with the protection of public health and welfare
against hearing loss, annoyance, and activity interference. It has been used as the basis of
numerous community noise standards and ordinances.
2. Committee on Hearing, Bioacoustics and Biomechanics (CHABA) Working Group
69, "Guidelines for Preparing Environmental Impact Statements on Noise”
(
75
)
This report was the result of deliberations by a group of leading acoustical scientists with the
goal of developing a uniform national method for noise impact assessment. Although the
CHABA's proposed approach has not been adopted, the report serves as an excellent resource
documenting research in noise effects. It provides a strong scientific basis for quantifying impacts
in terms of L
dn
.
3. American Public Transportation Association (APTA) Guidelines for Design of Rapid
Transit Facilities
(
76
)
The noise and vibration sections of the APTA Guidelines have been used successfully in the past
for the design of rail transit facilities. The APTA Guidelines include criteria for acceptable
community noise and vibration. Experience has shown that meeting the APTA Guidelines will
usually result in acceptable noise levels; but the metric used in the APTA Guidelines is not
appropriate for environmental assessment purposes.
The APTA Guidelines criteria are in terms of
L
max
for conventional RRT vehicles, and they
cannot be used to compare among different modes of transit. Since the APTA Guidelines are
expressed in terms of maximum passby noise, they are not sensitive to the frequency or
duration of noise events for transit modes other than conventional RRT operations with 5 to 10
minute headways. Therefore, the APTA criteria are questionable for assessing the noise impact
of other transit modes that differ from conventional rapid transit with respect to source
emission levels and operating characteristics (e.g., commuter rail, AGT, and a variety of bus
projects).
4. Synthesis of Social Surveys on Noise Annoyance
(
77
)
In 1978, Theodore J. Schultz, an internationally known acoustical scientist, synthesized the
results of a large number of social surveys concerning annoyance due to transportation noise. A
group of these surveys were remarkably consistent, and the author proposed that their average
FEDERAL TRANSIT ADMINISTRATION 217
results be taken as the best available prediction of transportation noise annoyance. This
synthesis has received essentially unanimous acceptance by acoustical scientists and engineers.
The "universal" transportation response curve developed by Schultz (Figure 3-7) shows that the
percent of the population highly annoyed by transportation noise increases from zero at an L
dn
of approximately 50 dBA to 100% when L
dn
is approximately 90 dBA. Most importantly, this
curve indicates that for the same increase in L
dn
, there is a greater increase in the number of
people highly annoyed at high noise levels than at low noise levels. For example, a 5 dB increase
at low ambient levels (40 - 50 dB) has less impact than at higher ambient levels (65 - 75 dB). A
recent update of the original research containing several railroad, transit, and street traffic noise
surveys, confirming the shape of the original Schultz curve
(12)
.
5. HUD’s Standards
(19)
HUD has developed noise standards, criteria, and guidelines to ensure that housing projects
supported by HUD achieve the goal of a suitable living environment. The HUD acceptability
standards define 65 dB (L
dn
) as the threshold for a normally unacceptable living environment
(moderate impact for FTA) and 75 dB (L
dn
) as the threshold for an unacceptable living
environment (severe impact for FTA).
C.2 Basis for Noise Impact Criteria Curves
The lower curve in Figure 4-2 represents the onset of moderate impact and is based on the following
considerations:
The EPA finding that a community noise level of L
dn
less than or equal to 55 dBA is "requisite to
protect public health and welfare with an adequate margin of safety."
(72)
The conclusion by EPA and others that a 5 dB increase in L
dn
or L
eq(1hr)
is the minimum required
for a change in community reaction.
The research concludes that there are very few people highly annoyed when the L
dn
is 50 dBA,
and that an increase in L
dn
from 50 dBA to 55 dBA results in an average of 2% more people
highly annoyed (Figure 3-7).
The increase in noise level from an existing ambient level of 50 dBA to a cumulative level of 55 dBA
because of a project is found to cause minimal impact, with 2% of people highly annoyed, as described in
the bullets above. This is considered the lowest threshold where impact starts to occur. Therefore, for
an existing ambient noise level of 50 dBA, the curve representing the onset of moderate impact is at 53
dBA, the combination of which yields a cumulative level of 55 dBA by decibel addition. The remainder of
the lower curve in Figure 4-2 was determined from the annoyance curve (Figure 3-7) by allowing a fixed
2% increase in annoyance at other levels of existing ambient noise. As cumulative noise increases, the
increment to attain the same 2% increase in highly annoyed people is smaller. While it takes a 5-dB
noise increase to cause a 2% increase in highly annoyed people at an existing ambient noise level of 50
dB, an increase of only 1 dB causes a 2% increase of highly annoyed people at an existing ambient noise
level of 70 dBA.
The upper curve in Figure 4-2 represents the onset of severe impact based on a total noise level,
corresponding to a higher degree of impact. The severe noise impact curve is based on the following
considerations:
HUD defines an L
dn
of 65 as the onset of a normally unacceptable noise zone (moderate impact
for FTA) in its environmental noise standards
(19)
. FAA considers that residential land uses are
not compatible with noise environments where L
dn
is greater than 65 dBA (20).
FEDERAL TRANSIT ADMINISTRATION 218
An increase of 5 dB in L
dn
or L
eq(t)
is commonly assumed as the minimum required increase for a
c
hange in community reacti
on.
T
he research concludes that an increase of 5 dB in L
dn
or L
eq(t)
represents a 6.5% increase in the
number
of people highly annoyed (Figure 3-7
).
T
he increase in noise level from an existing ambient level of 60 dBA to a cumulative level of 65 dBA
caused by a project represents a change from an acceptable noise environment to the threshold of an
unacceptable noise environment. This is considered the level at which severe impact starts to occur
with a 6.5% increase in the number of people highly annoyed as described in the bullets above.
Therefore, for an existing ambient noise level of 60 dBA, the curve representing the onset of severe
impact is at 63 dBA, the combination of which yields a cumulative level of 65 dBA by decibel addition.
The remainder of the upper curve in Figure 4-2 was determined from the annoyance curve (Figure 3-7)
by allowing a fixed increase of the 6.5% increase in annoyance at all existing ambient noise levels.
Both curves incorporate a maximum limit for the transit project noise in noise-sensitive areas.
Independent of existing noise levels, moderate impact for land use categories 1 and 2 is considered to
occur whenever the transit L
dn
equals or exceeds 65 dBA, and severe impact occurs whenever the
transit L
dn
equals or exceeds 75 dBA. These absolute limits are intended to restrict activity interference
caused by the transit project alone.
Both curves also incorporate a maximum limit for cumulative noise increase at low existing noise levels
(below approximately 45 dBA). This is a conservative limit that reflects the lack of social survey data on
people's reactions to noise at such low ambient levels. Like the FHWA approach in assessing the relative
impact of a highway project, the transit noise criteria include limits on noise increase of 10 dB and 15 dB
for moderate impact and severe impact, respectively, relative to the existing noise level.
Note that due to the types of land use included in category 3, the criteria allow the project noise for
category 3 sites to be 5 dB greater than for category 1 and category 2 sites. This difference is reflected
by the offset in the vertical scale on the right side of Figure 4-2. Aside from active parks, which are
clearly less sensitive to noise than category 1 and 2 sites, category 3 sites include primarily indoor
activities. Therefore, the criteria account for some noise reduction from the building structure.
C.3 Equations for Noise Impact Criteria Curves
The equations for the noise impact criteria curves shown in Figure 4-2 are included in this section.
These equations may be useful when performing the noise assessment methodology using spreadsheets,
computer programs, or other analysis tools. Otherwise, such mathematical detail is generally not
necessary to implement the criteria, and direct use of Figure 4-2 is adequate and less time-consuming.
A total of four continuous curves are included in the criteria, creating two threshold curves for
moderate and severe impact for category 1 and 2, and two curves for category 3 (See Table C-1). Note
that for each level of impact, the overall curves for categories 1 and 2 are offset by 5 dB from category
3. While
each curve is graphically continuous, each one is defined by a set of three discrete equations
.
T
hese equations are approximately continuous at the transition points. The following is a description
of
t
he three equations
:
The first equation in each set is a linear relationship, representing the portion of the curve in
whi
ch the existing noise exposure is low, and the allowable increase is limited to 10 dB and
15
dB for moderate impact and severe impact, respectively.
FEDERAL TRANSIT ADMINISTRATION 219
Threshold of Moderate Impact
Category 1 and 2
Category 3
Eq. C- 12
Eq. C- 13
Threshold of Severe Impact
Category 1 and 2
Category 3
Eq. C- 14
Eq. C- 15
The second equation in each set represents the impact threshold over the range of existing
nois
e exposure for which a fixed percentage of increase in annoyance is allowed, as described
in
A
ppendix C.2. This curve is a third-order, polynomial approximation derived from the Schult
z
c
urve
(75)
and covers the range of noise exposure encountered in most populated areas. This
c
urve is used for determining noise impact in most cases for transit projects
.
The third equation represents the absolute limit of project noise imposed by the criteria for
a
reas with high existing noise exposure. For land use category 1 and 2, the absolute limit is 6
5
dB
A for moderate impact and 70 dBA for severe impact. For land use category 3, the absolut
e
li
mit is 75 dBA for moderate impact and 80 dBA for severe impact
.
Table C-1 Threshold of Moderate and Severe Impacts
= the existing noise exposure in terms of L
dn
or L
eq(1hr)
= the project noise exposure which determines impact in terms of L
dn
or L
eq(1hr)
)
FEDERAL TRANSIT ADMINISTRATION 220
Appendix D: Clustering Receivers of Interest
This appendix supplements the information in Section 4.5 on clustering receivers of interest.
The general approach to selecting noise-sensitive receivers in the study area is included in Section 4.5,
Step 1. General guidelines are as follows:
Select the following types of receivers to evaluate individually:
Every major noise-sensitive public building
Every isolated residence
Every relatively small outdoor noise-sensitive area
Residential neighborhoods and relatively large outdoor noise-sensitive areas can often be
clustered and represented by a single receiver.
Clustering similar receivers reduces the number of computations needed later, especially for large-scale
projects where a greater number of noise-sensitive sites may be affected. For this approach to be
effective, it is essential that the representative receiver accurately represents the noise environment of
the cluster.
The major steps in clustering receivers include:
1. First, cluster receivers according to approximately equal exposure to the primary project noise
source. These areas typically run parallel to a linear project or circle major stationary sources
relative to the proposed project.
2. Next, cluster receivers according to major sources of ambient noise. These areas typically run
parallel to or encircle major sources of ambient noise.
3. Then, cluster receivers according to changes in the project layout or operations along the
corridor.
4. Finally, select a representative receiver for each cluster.
The major steps are expanded below and include instructions on how to draw cluster boundaries on a
map.
1. Boundaries along the proposed project – Draw cluster boundaries along the proposed project
as described below to separate clusters based on distance from the project. Draw these cluster
boundaries for the project sources listed as major in Table 4-19.
Within both residential and noise-sensitive outdoor areas:
Primary project source
Draw cluster boundaries at the following distances from the near edge of the primary
project source: 0 ft, 50 ft, 100 ft, 200 ft, 400 ft, and 800 ft. For linear sources, such as a rail
line, draw these boundaries as lines parallel to the proposed ROW line. For stationary
sources, draw these boundaries as approximate circles around the source, starting at the
property line.
Do not extend boundaries beyond the noise study area, identified in the Noise Screening
Procedure in Section 4.3 or the General Noise Assessment of Section 4.4.
FEDERAL TRANSIT ADMINISTRATION 221
Remaining project sources – Repeat the process for the primary project source for all other
project listed as major in Table 4-19, such as substations and crossing signals. If several project
sources are located approximately together, only consider one source, since the others would
produce approximately the same boundary.
It is good practice to optimize the number of clusters for a project to simplify the procedure.
Where rows of buildings parallel the transit corridor:
Ensure that cluster boundaries fall between the following rows of buildings, counting back
away from the proposed project:
Between rows 1 and 2
Between rows 2 and 3
Between rows 3 and 4
Add cluster boundaries between these rows if not already included.
2. Boundaries along sources of ambient noise – Draw cluster boundaries along all major sources
of ambient noise based upon distance from these sources, as described below.
Draw cluster boundaries along all interstates and major roadway arterials at the following
distances from the near edge of the roadway: 0 ft, 100 ft, 200 ft, and 500 ft.
Draw cluster boundaries along all other roadways that have state or county numbering at 0 ft
and 100 ft from the near edge of the roadway.
For all major industrial sources of noise, draw cluster boundaries that encircle the source at the
following distances from the near property line of the source: 0 ft, 100 ft, 200 ft, and 400 ft.
3. Boundaries based on changes in project layout or operations – Further subdivision is
needed to account for changes in project noise where proposed project layout or operating
conditions change considerably along the corridor. Draw a cluster boundary perpendicular to the
corridor extending straight outward to both sides at the following locations:
Where parallel tracks previously separated by more than approximately 100 ft are moved closer
together
Approximately where speed and/or throttle are reduced when approaching stations and where
steady service speed is reached after departing stations
Approximately 200 ft up and down the line from grade crossing bells
At transitions from jointed to welded rail
At transitions from one type of cross section to another including on structure, on fill, at-grade
and in cut
At transitions from open terrain to heavily wooded terrain
At transitions between areas free of locomotive horn noise and areas subject to this noise
source
Any other positions along the line where project noise is expected to change considerably, such
as up and down the line from tight curves where wheels may squeal
4. Selection of a representative receiver from each cluster – Determine a representative
receiver for each cluster boundary drawn in the steps above.
Residential clusters
Select a representative receiver within the cluster at the house closest to the proposed project.
If this receiver is not the clear choice, select the receiver furthest from major sources of
ambient noise.
Outdoor noise-sensitive clusters (e.g., urban park or amphitheater)
FEDERAL TRANSIT ADMINISTRATION 222
Select a representative receiver within the cluster at the closest point of active noise-sensitive
use. If this receiver is not the clear choice, select the receiver farther from major sources of
ambient noise.
Note that some clusters may fall between areas with receivers of interest. This could occur when
operational changes or track layouts change in an open, undeveloped area. Retain these clusters. Do not
merge them with adjacent clusters. Do not select a representative receiver of interest from them.
Example D-1 Clustering Receivers
Receivers of Interest and Clustering Receivers
In this hypothetical situation, a new rail transit line, labeled "new rail line" in Figure D-1, is proposed along a major
urban street with commercial land use. A residential area is located adjacent to the commercial strip, located
approximately one-half block from the proposed transit alignment. A major arterial, labeled "highway," crosses the
alignment.
Cluster Receivers Along the Primary Project Source
Primary Project Source
The primary project source in this example is the new rail line. Boundaries are first drawn at distances of 0 ft from
the right-of- way line (edge of the street in this example), 50 ft, 100 ft, 200 ft, 400 ft, and 800 ft, (Figure D-1).
Distances are labeled at the top of the figure.
This is proposed to be a constant speed section of track, so there are no changes in boundaries due to changes in
operations along the corridor. Moreover, no other project sources are shown here, but if there had been a station
with a parking lot, lines would have been drawn enveloping the station site at the specified distances from the
property line.
Rows of Buildings Parallel to the Transit Corridor
This example includes rows of buildings parallel to the transit corridor. The first set of boundary lines satisfies the
requirement that cluster boundaries fall between rows 1 and 2, and between rows 2 and 3, but there is no line
between rows 4 and 5. Consequently, a cluster boundary labeled "R" at the top of the figure has been drawn
between the 4th and 5th row of buildings.
Cluster Receivers Along the Primary Project Source
The roadway arterial (labeled "highway") is the only major source of ambient noise shown.
Cluster boundaries are drawn at 0 ft, 100 ft, 200 ft and 500 ft from the near edge of the roadway on both sides.
These lines are shown with distances labeled at the side of the figure.
Select a Representative Receiver from Each Cluster
Representative receivers are shown as filled circles in Figure D-1. Note that the receivers labeled with “REC” are
primarily for use in Appendix E.
Locate receiver, "REC 3". Note that this cluster is located at the outer edge of influence from the major source
("highway") where local street traffic is the dominant source for ambient noise (in practice, this would be verified
by a measurement).
"REC 3" is chosen to represent this cluster because it is among the houses closest to the proposed project source
in this cluster and it is in the middle of the block affected by the dominant local street. Ambient noise levels at one
end of the cluster may be influenced more by the highway and the other end may be affected more by the cross
street, but the majority of the cluster would be represented by receiver site "REC 3."
FEDERAL TRANSIT ADMINISTRATION 223
Figure D-1 Example of Receiver Map Showing Cluster Boundaries
FEDERAL TRANSIT ADMINISTRATION 224
Appendix E: Determining Existing Noise
Different options of determining existing noise, including full measurement, computation from partial
measurements, and tabular look-up, are described in Section 4.5, Step 5. This appendix provides
additional details associated with each method and examples of when each method could be used.
Additional details on the methods for estimating existing noise are provided below:
Option 1: L
eq(1hr)
measurement (non-residential) – Full one-hour measurements are
recommended to determine existing noise for non-residential receivers of interest. These
measurements are preferred over all other options and will accurately represent the L
eq(1hr)
. The
following procedures apply to these full-duration measurements:
Measure L
eq(1hr)
at the receiver of interest during a typical hour of use on two non-successive
days. Choose the hour in which maximum project activity will occur. The L
eq(1hr)
will be
accurately represented using this method. Typically, measuring between noon Monday and noon
Friday is recommended, but weekend days may be more appropriate for places of worship.
Position the measurement microphone for all sites as shown in Figure 4-19, considering relative
orientation of project and ambient sources. Position the microphone in a location that is
somewhat shielded from the ambient source to measure the ambient noise at these locations at
the quietest area on the property.
Conduct all measurements in accordance with good engineering practice.
Option 2: L
dn
measurement (residential) – Full 24-hour measurements are recommended to
determine ambient noise for residential receivers of interest. These measurements are preferred over
all other options and will accurately represent the L
dn
. The following procedures apply to these full-
duration measurements:
Measure a full 24-hour L
dn
at the receiver of interest for a single weekday (generally between
noon Monday and noon Friday).
Position the measurement microphone for all sites as shown in Figure 4-19 considering relative
orientation of project and ambient sources. Position the microphone in a location that is
somewhat shielded from the ambient source to measure the ambient noise at these locations at
the quietest area on the property.
Conduct all measurements in accordance with good engineering practice.
Option 3: L
dn
computation of L
dn
from 3 partial L
eq(1hr)
measurements (residential) – An
alternative way to determine L
dn
is to measure L
eq(1hr)
for three typical hours of the day, then compute
the L
dn
from these three L
eq(1hr)
measurements. This method is less precise than its full-duration
measurement. The following procedures apply to this partial-duration measurement method for L
dn
:
Measure the L
eq(1hr)
during each of the following time periods:
During peak-hour roadway traffic
Midday, between the morning and afternoon roadway-traffic peak hours
During late night between midnight and 5 a.m.
Position the measurement microphone for all sites as shown in Figure 4-19 considering relative
orientation of project and ambient sources. Position the microphone in a location that is
somewhat shielded from the ambient source to measure the ambient noise at these locations at
the quietest area on the property.
Conduct all measurements in accordance with good engineering practice.
Compute the L
dn
using the equation below
FEDERAL TRANSIT ADMINISTRATION 225
Eq. E-1
For measurements between 7 p.m. and 10 p.m.:
For measurements between 10 p.m. and 7 a.m.:
The resulting L
dn
will be slightly underestimated due to the adjustment to the measured levels in these
equations. This underestimation is intended to compensate for the reduced precision of the computed
L
dn
. If using this method, a minimum time duration of one hour should be used for each measurement
period in computing an Ldn.
Option 4: Computation of L
dn
from 1 partial L
eq(1hr)
measurement (residential) – L
dn
can also
be determined by measuring L
eq(1hr)
for one hour of the day, and then computing L
dn
from the L
eq(1hr)
.
This method is less precise than computing L
dn
from 3 L
eq(1hr)
measurements. This method may be useful
for projects with are many sites assessed by the General Noise Assessment. This method may also be
appropriate when determining if a particular receiver of interest represents a cluster in a Detailed Noise
Analysis. The following procedures apply to this partial-duration measurement option for L
dn
:
Measure the L
eq(1hr)
for the loudest hour of project-related activity during hours of noise
sensitivity
. If this hour is not selected, other hours may be used with the understanding that the
es
timate is less precise
.
Position the measurement microphone for all sites as shown in Figure 4-19, considering relative
ori
entation of project and ambient sources. Position the microphone in a location that
is
s
omewhat shielded from the ambient source to measure the ambient noise at these locations a
t
t
he quietest area on the property
.
Conduct
all measurements in accordance with good engineering practic
e.
Conve
rt the measured hourly L
eq(1hr)
to L
dn
with the appropriate equation below.
For measurements between 7 a.m. and 7 p.m.:
Eq. E-2
Eq. E-3
Eq. E-4
The resulting L
dn
will be moderately underestimated due to the use of the adjustment constants in these
equations. This underestimation is intended to compensate for the reduced precision of the computed
L
dn
. If using this method, a minimum time duration of one hour should be used for each measurement
period in computing an Ldn.
Option 5: Computation of L
eq(1hr)
or L
dn
from L
eq(1hr)
or L
dn
of a comparable site (all land
uses) – Computing L
eq(1hr)
or L
dn
from the L
eq(1hr)
or L
dn
of a comparable site where the ambient noise is
dominated by the same source that is comparable in precision to Option 4. This method can be used to
characterize noise in several neighborhoods by using a single representative receiver. It is critical that
the measurement site has a similar noise environment to all areas represented. If measurements made
by others are available and the sites are equivalent, the existing measurements can be used to reduce
the amount of project noise monitoring. The following procedures apply to this method of determining
of ambient noise:
Choose another receiver that is comparable to the receiver (CompRec) of interest with t
he
following:
T
he same source of dominant ambient nois
e
FEDERAL TRANSIT ADMINISTRATION 226
If roadway sources dominate:
Eq. E-5
If other sources dominate:
Eq. E-6
The ambient level of the comparable receiver was measured according to Option 1 or
Opt
ion 2 above
The ambient measurement at the comparable receiver was made in direct view of the major
source of ambient noise, unshielded by noise barriers, terrain, rows of buildings, or dense
tree zones
Determine the following from a plan or aerial photograph:
The distance (D
CompRec
) from the comparable receiver to the near edge of the ambient
source
The distance (D
Rec
) from this receiver of interest to the near edge of the ambient source
Determine the number of rows of buildings (N) that intervene between the receiver of interest
and the ambient source.
Compute the ambient level at the receiver of interest (Rec) with the appropriate equation
below
The resulting L
Rec
will be moderately underestimated. This underestimation is intended to compensate
for the reduced precision of the computed L
dn
.
Option 6: Estimation of L
dn
by table look-up (all land uses) – The least precise way to determine
the ambient noise is to estimate the level using a table. A tabular look-up can be used to establish
baseline conditions for a General Noise Assessment if a noise measurement cannot be made. This
method should not be used for a Detailed Noise Analysis. The following instruction applies to this
method of determining of ambient noise:
Estimate either the L
eq(1hr)
or the L
dn
using Table 4-17 based on distance from major roadways, rail lines,
or upon population densities. In general, these tabulated values are substantially underestimated.
The underestimation is intended to compensate for the reduced precision of the estimated ambients.
Examples – Examples of when each method of determining existing noise may be appropriate are
provided below using the example from Appendix D. Existing noise at the receivers labeled “REC” in
Figure D-1 could be estimated as follows:
Option 1: L
eq(1hr)
measurement – Existing noise at REC 1 is due to the highway at the side
of this church. L
eq(1hr)
can be measured during a typical church hour.
Option 2: L
dn
measurement – Existing noise at the residence REC 2 is due to a combination
of the highway and local streets. L
dn
can be measured for a full 24-hours.
Option 3: L
dn
computation of L
dn
from 3 partial L
eq(1hr)
measurements – Existing noise
at the residence REC 3 is due to the street in front of this residence. L
dn
can be computed from
three L
eq(1hr)
measurements.
FEDERAL TRANSIT ADMINISTRATION 227
Option 4: Computation of L
dn
from 1 partial L
eq(1hr)
measurement – Existing noise at
t
he residence REC 4 is due to the highway. Because the highway has a predictable diurna
l
pa
ttern, L
dn
can be computed from one L
eq(1hr)
measurement.
O
ption 5: Computation of L
dn
from L
dn
of a comparable site – Existing noise at the
r
esidence REC 5 is due to Kee Street. REC 3 is also affected by local street traffic and is
a
comparable distance from the highway. L
dn
for REC 5 can be computed based on the L
dn
at
R
EC-
3.
O
ption 6: Estimation of L
dn
by table look-up – Existing noise at the residence REC 6 is due
t
o local traffic. L
dn
can be estimated by tables based on population density along this corridor.
FEDERAL TRANSIT ADMINISTRATION 228
Appendix F: Computing Source Levels from
Measurements
This appendix contains the procedures for computing source reference levels (SEL
ref
) from source
measurements in cases where the source reference tables in Section 4.5, Step 2 indicate measurements
are preferred, data are not available for the source of interest, or more precise data are required than
available in the table.
Close-by source measurements for vehicle passbys may capture either the vehicle's sound exposure
level (SEL) or maximum noise level (L
max
). Both metrics can be measured directly by commonly available
sound level meters. While the L
max
metric is not used for transit noise impact assessments, it can be
used to compute SEL source reference levels. L
max
measurements are often available from transit-
equipment manufacturers and some transit system equipment specifications may limit close-by L
max
levels.
Close-by source measurements for stationary sources capture the source’s SEL over one source event,
where the event duration may be chosen based on measurement convenience. The duration will factor
out of the computation when the measured value is converted to reference operating conditions.
This manual does not specify elaborate methods for undertaking the close-by source measurements, but
rather, provides general processes. It is required that all measurements conform to good engineering
practice, guided by the standards of the American National Standards Institute and other such
organizations (27, 28, 29).
This appendix presents information according to noise source as follows:
Appendix F.1: Highway and rail vehicle passbys for vehicles of the same type
Appendix F.2: Stationary sources
Appendix F.3: L
max
for single train passbys (for trains of mixed consists)
F. 1 Highway and Rail Vehicle Passbys
This section provides information on appropriate conditions for vehicle passby measurements,
instructions on converting measurements made under non-reference conditions to source reference
levels, and examples of these computations.
The following conditions are required for vehicle passbys, in addition to good engineering practice:
Measured vehicles must be representative of project vehicles in all aspects, including
representative acceleration and speed conditions for buses.
Track must be relatively free of corrugations and train wheels relatively free of flats, unless
these conditions are typical of the proposed project.
Road surfaces must be smooth and dry, unless these conditions are typical of the proposed
project.
Perpendicular distance between the measurement position and the source's centerline must be
100 ft or less.
Vehicle speed must be 30 mph or greater, unless typical project speeds are less than that.
No noise barriers, terrain, buildings, or dense tree zones may break the lines-of-sight between
the source and the measurement position.
FEDERAL TRANSIT ADMINISTRATION 229
When close-by source measurements are made under non-reference conditions, use the instructions
below and the equations in Table F-1 to convert the measured values to source reference levels. For rail
vehicles, measure/convert a group of locomotives or a group of cars separately. This computation
requires that all measured vehicles be of the same type. For trains of mixed consists, see Appendix F.3.
SEL measured for a highway-vehicle passby, or a passby of a group of identical rail vehicles
Collect the following input infor
mation:
SEL
meas
, the measured SEL for the vehicle passby
N,
the consist of the measured group of rail cars or group of locomotiv
es
T, the average throttle setting of the measured diesel-powered locomotive(s)
S
meas
, the measured passby speed, in miles per hour
D
meas
, the closest distance between the measurement position and the source, in feet
Compu
te the Source Reference Level SEL
ref
, using Eq. F-1.
L
max
measured for a passby of a group of identical rail vehicles
Collect the following input infor
mation:
L
max
, measured for the group passby
N,
the consist of the measured group of rail cars or group of locomotiv
es
T, the average throttle setting of the measured diesel-powered locomotive(s)
S
meas
, the measured passby speed, in miles per hour
D
meas
, the closest distance between the measurement position and the source, in feet
L
meas
, the total length of the measured group of locomotives or group of rail cars, in feet
C
ompute the Source Reference Level SEL
ref
, using either Eq. F-2 or Eq. F-3, as appropriate, for
locomo
tives or rail cars
.
L
max
measured for a highway-vehicle passby
Collect the following input infor
mation:
L
max
, measured for the highway-vehicle passby
S
meas
, the vehicle speed, in miles per hour
D
meas
, the closest distance between the measurement position and the source, in feet
Compu
te the Source Reference Level, SELref, using Eq. F-4
.
FEDERAL TRANSIT ADMINISTRATION 230
Table F-1 Conversion to Source Reference Levels at 50 ft – Highway and Rail Sources
Measured
Source
Equation
SEL
Vehicle
passby
Eq. F-1
L
max
Rail-vehicle
passby,
locomotives
only
Eq. F-2
Rail-vehicle
passby,
cars only
Eq. F-3
Highway-
vehicle
passby
Eq. F-4
S
meas
= speed of measured vehicle(s), mph
D
meas
= closest distance between measurement position and source, ft
C
consist
= 0 for buses and automobiles
for locomotives and rail cars
where N is the number of locomotives or rail cars in the measured group
C
emission
= 0
for T < 6
for locomotives
-2 (T-5)
for T ≥ 6
s
where T is average throttle setting of measured diesel – electric locomotive(s)
for rail cars
for buses
for automobiles
E
meas
= event duration of measurement, sec
L
meas
= total length of measured group of locomotives or rail cars, ft
= arctan( rad
FEDERAL TRANSIT ADMINISTRATION 231
Example F-1 Calculate SEL
ref
– Locomotives
Computation of SEL
ref
from SEL Measurement of Fixed-guideway Source
SEL was measured for a passby of two diesel-powered locomotives with the following conditions:
SEL
meas
= 90 dBA
= 2
T
= 6
S
meas
= 55 mph
D
meas
= 65 ft
Compute the source reference level using Eq. F-1.
= 86.5 dBA
Example F-2 Calculate SEL
ref
– Rail Cars
Computation of SEL
ref
from L
max
Measurement of Fixed-Guideway Source
L
max
was measured for a passby of a 4-car consist of 70-ft long rail cars with the following conditions:
L
max
= 90 dBA
= 4
S
meas
= 70 mph
D
meas
= 65 ft
L
meas
= 280 ft
= 1.14
Compute the source reference level using Eq. F-3.
= 86.7 dBA
FEDERAL TRANSIT ADMINISTRATION 232
Example F-3 Calculate SEL
ref
– Bus
Computation of SEL
ref
from L
max
Measurement of Highway Vehicle Source
L
max
was measured for a bus with the following conditions:
L
max
= 78 dBA
D
meas
= 80 ft
S
meas
= 40 mph
Compute the source reference level using Eq. F-4
= 87.8 dBA
F.2 Stationary Sources
This section provides information on appropriate conditions for stationary source measurements,
instructions on converting measurements made under non-reference conditions to source reference
levels, and an example of this type of computation.
The following conditions are required for stationary sources, in addition to good engineering practice:
Measured source operations must be representative of project operations in all aspects
.
T
he following ratio must be 2 or less, and the distance to the closest source component mus
t
be
200 ft or less
.
If both conditions cannot simultaneously be met, separate close-by measurements of individual
components of this source must be made, for which these distance conditions can be met.
The following ratio must be 2 or less
:
The lateral length of the source area is measured perpendicular to the general line-of-sight
between source and measurement positions.
If this condition cannot be met, then make separate close-by measurements of individual
components of this source, for which this condition can be met.
No noise barriers, terrain, buildings, or dense tree zones may break the lines-of-sight betw
een
t
he source and the measurement positi
on.
When
close-by source measurements are made under non-reference conditions, use the instructions
below and the equation in Table F- 2 to convert the measured values to source reference levels.
FEDERAL TRANSIT ADMINISTRATION 233
SEL was measured for a stationary noise source
Collect the following input infor
mation:
SEL
meas
, the measured SEL for the noise source, for whatever source "event" is convenient
t
o measur
e
E
meas
, the event duration, in seconds
D
meas
, the closest distance between the measurement position and the source, in feet
Compu
te the source reference level, SELref using Eq. F-
5.
Table F-2 Conversion to Source Reference Levels at 50 ft - Stationary Sources
Measured
Source
Equation
SEL
Stationary
noise source
Eq. F- 5
S
meas
= speed of measured vehicle(s), in miles per hour
E
meas
= event duration of measurement, in seconds
D
meas
= closest distance between measurement position and source, in feet
Example F-4 Calculate SEL
ref
– Signal Crossing
Computation of SEL
ref
from SEL Measurement of Stationary Source
SEL was measured for a signal crossing with the following conditions:
SEL
meas
= 70 dBA
E
meas
= 10 sec
D
meas
= 65 ft
Compute the source reference level using Eq. F-5.
= 97.8 dBA
F.3 L
max
for Single Train Passby
This section provides procedures for the computation of L
max
for a single train passby. This procedure
can be used to characterize trains of mixed consists using L
max
. Follow the instructions below.
Collect the following input information:
SEL
ref
, from Section 4.5, specific to both the locomotive type and car type of the train
N
loco
, the number of locomotives in the train
N
cars
, the number of cars in the train
L
loco
, the total length of the train's locomotive(s), in feet (or N
loco
unit length)
L
cars
, the total length of the train's set of rail car(s), in feet (or N
cars
unit length)
S,
the train speed, in miles per
hour
D, the closest distance between the receiver of interest and the train, in feet
Use the equations in Table F-3 to compute the following:
L
max.loco
for the locomotive(s) using Eq. F-6
FEDERAL TRANSIT ADMINISTRATION 234
L
max.cars
for the rail car(s) using the Eq. F-7
L
max.total
, the larger L
max
from the locomotives(s) and rail car(s) is the L
max
for the total train
pa
ssby, see Eq. F-
8.
Table F-3 Conversion to Lmax at the Receiver, for a Single Train Passby
Source
Equation
Locomotives
Eq. F-6
Rail Cars
Eq. F-7
Total Train
Eq. F-8
L
= total length of measured group of locomotive(s) or rail car(s), ft
S
= vehicle speed, mph
= arctan , rad
D
= closest distance between receiver and source, ft
FEDERAL TRANSIT ADMINISTRATION 235
Example F-5 Calculate L
max
– Train Passby
Computation of L
max
for Train Passby
Calculate the L
max
of commuter train at receiver of interest according to the following conditions:
SEL
ref
= 92 dBA for locomotives
= 82 dBA for rail cars
= 1
= 6
S
= 43 miles per hour
D
= 125 ft
= 0.27
= 1.03
The locomotive and rail cars each have a unit length (L) of 70 ft.
Determine the total length of the locomotive and rail cars.
L
Loco
= 70 ft
L
cars
= 420 ft
Compute L
max
for the locomotive using Eq. F-6:
= 84.0 dBA
Compute L
max
for the rail cars using Eq. F-7:
= 73.5 dBA
Find the total L
max
for the train passby using Eq. F-8.
=84.0 dBA
FEDERAL TRANSIT ADMINISTRATION 236
Appendix G: Non-Standard Modeling Procedures and
Methodology
This manual provides guidance for preparing and reviewing the noise and vibration sections of
environmental documents, as well as FTA-approved methods and procedures to determine the level of
noise and vibration impact resulting from most federally-funded transit projects. Situations may arise,
however, that are not explicitly covered in this manual. Professional judgment may be used to extend
the basic methods to cover these cases, when appropriate. It is important to note that each project is
unique and must be evaluated on a case-by-case basis. This appendix provides procedures for the use of
non-standard noise and vibration modeling procedures and methodologies on public transportation
projects.
Submittal Procedure – The procedure for using non-standard modeling procedures and
methodology is as follows:
1. The transit project manager should contact the FTA Regional office to discuss the proposed
methods and/or data not described in this manual prior to use of the non-standard approach.
2. The non-standard methodology should be documented according to the guidelines below as
part of the technical report described in Section 8.2.
Examples of Methods that Require Communication and Documentation – The following
noise and vibration analysis methods and data require communication with the FTA Regional office and
documentation:
Non-standard transit noise and vibration modeling and analysis methods not described in this
manual (including non-standard adjustments, computations, and assumptions). This includes
modifications to standard FTA noise and vibration methods.
Non-standard transit noise and vibration reference data not described in this manual (including
measured data, substitution data, data at non-standard reference distances and/or speeds, new
transit noise sources, and transit noise sources operating in non-standard conditions).
Non-standard transit noise and vibration impact criteria not described in this manual, including
the maximum sound pressure level metric.
Non-standard methods of evaluating construction noise, including non-standard construction
noise impact criteria.
Other noise modeling tools besides the FTA Noise Impact Assessment Spreadsheet or Traffic
Noise Model (TNM®) for highway noise modeling, such as the development of a finite element
method model.
Any transit noise and vibration analysis that involves an impact area or noise source that is
controversial.
Documentation Guidelines – The use of non-standard noise and vibration analysis methods or data
requires the following documentation components in a technical memorandum attached to the
environmental document:
Background
Briefly describe the transit project for which non-default methods or data are needed. State the
dominant noise sources, type of analysis, and the impact criteria. Include any additional relevant
information.
FEDERAL TRANSIT ADMINISTRATION 237
Statement of Benef
it
Bri
efly describe the benefit of the non-default noise and vibration methods or data to the trans
it
pr
oject. Describe the appropriateness of the non-default methods or data, as well as why t
he
s
tandard method or data are insufficient or problematic
.
N
on-standard Data Descriptio
n
Des
cribe the non-standard noise or vibration data in detail. Include source type, manufacturer
,
reference conditions (speed, distance, and operational conditions), name of data supplier, and a
date
associated with data development/measurement. For measured noise or vibration
data,
provide corresponding data documentation (such as a data measurement or a development
r
eport). For substitution data, a comparison between the non-standard data and correspond
ing
standard data should be provided. Furthermore, if outside sources recommend the use of the
non
-standard data (such as a technical society, a standards organization, or a vehic
le
manufa
cturer), references for those recommendations should be included
.
N
on-standard Methods Descriptio
n
Des
cribe the non-standard noise or vibration analysis method in detail. This should include
a
det
ailed description and derivation of the method (including data used in the development of t
he
met
hod), a description of the usage of the method, and a comparison between the non-standar
d
met
hod and the corresponding standard method in the context of the transit analysis. If t
he
met
hod has been validated against measurement data, a description of that validation analys
is
s
hould be provided. If the method is derived from another source (such as a differ
ent
t
ransportation noise or vibration method), provide corresponding documentation for tha
t
source. A description of how the method is conservative (for example, estimating the worst-
case scenario) or some discussion on the probability of exceeding the predicted level should
be
provided. Furthermore, if outside sources recommend the use of the non-standard method
(
such as a technical society or standards organization), references for those recommendat
ions
s
hould be included
.
N
on-standard Tools Descriptio
n
Des
cribe in detail any non-standard noise or vibration models that have not been explic
itly
r
ecommended in this manual. This should include a detailed description of the tool (includi
ng
data
used, the computations implemented in the tool, any modifications or adjustments to t
he
tool or the corresponding data, and the usage of the tool), a description of the validation of the
t
ool (including reference documentation and validation analyses), and a comparison between t
he
non-standard tool and the equivalent standard tool in the context of the transit analysis.
Q
uantitative comparisons, such as the standard deviation of the non-standard tool and a
n
estimate of the least mean square of differences between the standard and non-standard tools,
s
hould be provided and explained. A description of how the method is conservative (f
or
exa
mple, estimating the worst-case scenario) or some discussion on the probability of exc
eeding
t
he predicted level should be provided. If outside sources recommend the use of the non-
standard tool (such as a technical society or standards organization), references for th
ose
r
ecommendations should be inc
luded.
FEDERAL TRANSIT ADMINISTRATION 238
ENDNOTES
1
Regulations for Implementing the Procedural Provisions of the National Environmental Policy Act, Council on
Environmental Quality, 40 CFR parts 1500-1508, 1978.
2
National Environmental Policy Act of 1969, United States Congress, 42 U.S.C §4331, 1969.
3
U.S. Department of Transportation, Federal Transit Administration and Federal Highway Administration,
"Environmental Impact and Related Procedures," Final Rule, 52 Federal Register 32646-32669, January 2014 (23
CFR part 771).
4
U.S. Department of Transportation, Federal Transit Administration and Federal Highway Administration,
"Planning Assistance and Standards." Final Rule, 58 Federal Register 58064, June 2014 (23 CFR part 450).
5
U.S. Environmental Protection Agency, "Information on Levels of Environmental Noise Requisite to Protect
Public Health and Welfare with an Adequate Margin of Safety," Report No. 550/9-74-004, Washington DC,
March 1974.
6
Federal Interagency Committee on Urban Noise, "Guidelines for Considering Noise in Land Use Planning and
Control," Environmental Protection Agency, the Department of Transportation, the Department of Housing
and Urban Development, the Department of Defense, and the Veterans Administration, Washington DC, June
1980.
7
U.S. Department of Housing and Urban Development, "Environmental Criteria and Standards of the
Department of Housing and Urban Development,” Final Rule, 44 Federal Register 40861, Washington DC, 12
July 1979 (24 CFR part 51).
8
American National Standards Institute, "Compatible Land Use With Respect to Noise," Standard S3.23-1980,
New York NY, May 1980.
9
American National Standards Institute, “Quantities and Procedures for Description and Measurement of
Environmental Sound,” ANSI S12.9-1998/Part 5, New York. NY, January 1998.
10
T. J. Schultz, "Noise Rating Criteria for Elevated Rapid Transit Structures," U.S. Department of Transportation,
Report No. UMTA-MA-06-0099-79-3, Washington DC, May 1979.
11
T. J. Schultz, "Synthesis of Social Surveys on Noise Annoyance," Journal of the Acoustical Society of America, Vol.
63, No. 8, August 1978.
12
S. Fidell, D.S. Barber, T.J. Schultz, "Updating a Dosage-Effect Relationship for the Prevalence of Annoyance
D
ue to General Transportation Noise," Journal of the Acoustical Society of America, Vol. 89, No. 1, January 1991
.
13
S. Fidel, “The Schultz Curve 25-years Later: A Research Perspective,” Journal of the Acoustical Society of
Am
erica, Vol. 114, No. 6, Pt. 1, December 2003
.
14
“High-Speed Ground Transportation Noise and Vibration Impact Assessment”, DOT/FRA/ORD-12/15, U.S.
Department of Transportation Federal Railroad Administration, 2012.
15
National Historic Preservation Act, Section 106; P.L. 89-665, 15 October 1966.
16
The Department of Transportation Act of 1966, Section 4(f); P.L. 89-670, 15 October 1966.
17
U.S. Department of Transportation, Federal Transit Administration and Federal Highway Administration,
"Protection of Historic Properties." Final Rule, 65 Federal Register 77725, July 2013 (36 CFR 800).
FEDERAL TRANSIT ADMINISTRATION 239
18
“Eligibility and Justification Requirements for Noise Insulation Projects,” Program Guidance Letter 12-09,
November 2012. https://www.faa.gov/airports/aip/guidance_letters/historical_guidance_letters/media/aip-pgl-
2012-09-noise-insulation.pdf.
19
U.S. Department of Housing and Urban Development, “Environmental Criteria and Standards”, Vol. 12, July
1979; amended by 49 Federal Register 880, 6 January 1984 (24CFR part 51).
20
U.S. Department of Transportation, Federal Aviation Administration, “Federal Aviation Regulations Part 150:
Airport Noise Compatibility Planning,” January 1981.
21
U.S. Department of Transportation, Federal Railroad Administration, “Use of Locomotive Horns at Public
Highway-Rail Grade Crossings.” Final Rule, 70 Federal Register 21844, October 2013 (49 CFR 222).
22
U.S. Department of Transportation, Federal Highway Administration, “FHWA Traffic Noise Model User’s
Guide,” Report No. FHWA-PD-96-009, Washington, DC, January 1998. Also, “FHWA Traffic Noise Model
User’s Guide (Version 2.5 Addendum),” April 2004.
23
J.C. Ross, C.E. Hanson, R.V. Hartz, “Houston Southeast Corridor Environmental Impact Statement BRT Noise
a
nd Vibration Assessment,” technical memorandum prepared by Harris Miller Miller & Hanson fo
r
Me
tropolitan Transit Authority of Harris County Houston, Texas, September 20, 2005
.
24
U.S. Environmental Protection Agency, “Population Distribution of the United States as a Function of Outdoor
Noise Level,” Report No. 550/9-74-009, June 1974.
25
T. M. Johnson, "The Importance of Vehicle Throttle Setting Information for Rail Transit Noise Impact
A
ssessments," Proc. Inter-Noise 2012, New York, NY, August 2012
.
26
U.S. Department of Transportation, Federal Highway Administration, “FHWA Highway Traffic Noise
Prediction Model,” FHWA-RD-77-108, December 1978.
27
American National Standards Institute, “American National Standard Quantities and Procedures for
Description and Measurement of Environmental Sound, Part 4: Noise Assessment and Prediction of Long-term
Community Response,” ANSI 12.9-1996, New York, 1996.
28
C. Harris, “Handbook of Acoustical Measurements and Noise Control.”
29
International Organization for Standardization “Acoustics -- Attenuation of sound during propagation
ou
tdoors -- Part 2: General method of calculation.” ISO 9613-
2.
30
American Society for Testing and Materials, “Standard Guide for Measurement of Outdoor A-weighted Sound
L
evels,” E 1014-84, Philadelphia, 1984
.
31
American National Standards Institute, “Method for the Measurement of Sound Pressure Levels,” ANSI S1.
13
-1971(R1976), New York, 1971
.
32
U.S. Department of Transportation, Federal Highway Administration, “Measurement of Highway-Related
Noise,” FHWA-PD-96-046, May 1996.
33
J.T. Nelson, “Wheel/Rail Noise Control Manual,” Transportation Cooperative Research Report No. 23,
Transportation Research Board, Washington, DC, 1997.
34
“Challenges in Maintaining Quiet Streetcar and Light Rail Systems,” Session No. 409, Transportation Research
Board Annual Meeting, Washington DC, January 2014.
FEDERAL TRANSIT ADMINISTRATION 240
35
U.S. Department of Transportation, Federal Railroad Administration, “Use of Locomotive Horns at Highway-
Rail Grade Crossing,” Final Rule, 70 Federal Register 21844, April 27, 2005 (49 CFR 222).
36
“Interim Final Rule for the Use of Locomotive Horns at Highway-Rail Grade Crossings,” Federal Railroad
Administration, Final Environmental Impact Statement, December 2003.
37
T.A. Busch, R.E. Nugent, “A Reduced-Scale Railway Noise Barrier’s Insertion Loss and Absorption
Coefficients: Comparison of Field Measurements and Predictions,” Journal of Sound and Vibration, 749-759,
October 2003.
38
U.S. Department of Transportation, Federal Highway Administration, “Highway Noise Barrier Design
Package,” August 2000.
39
“High-Speed Ground Transportation Noise and Vibration Impact Assessment,” DOT/FRA/ORD-12/15, U.S.
Department of Transportation Federal Railroad Administration, 2012.
40
American National Standards Institute, “Guide to Evaluation of Human Exposure to Vibration in Buildings,”
ANSI S3.29-1983 (ASA 48-1983).
41
International Organization for Standardization, “Evaluation of Human Exposure to Whole-Body Vibration, Part
2: Continuous and Shock-Induced Vibrations in Buildings (1-80Hz),” ISO-2631-2, 1989.
42
International Organization for Standardization, “Mechanical Vibration and Shock: Evaluation of Human
Exposure to Whole Body Vibration: Part 2 – Vibration in Buildings (1 to 80 Hz),” ISO-2631-2, 2003.
43
J. T. Nelson, H. J. Saurenman, "State-of-the-Art Review: Prediction and Control of Ground-borne Noise and
Vibration from Rail Transit Trains," U.S. Department of Transportation, Urban Mass Transportation
Administration, Report No. UMTA-MA-06-0049-83-4, DOT-TSC-UMTA-83-3, December 1983.
44
Y. Tokita, "Vibration Pollution Problems in Japan," Inter-Noise 75, Sendai, Japan, 1975. (pp. 465-472)
45
J. A. Zapfe, H. Saurenman, S. Fidell, “Ground-Borne Noise and Vibration in Buildings Caused by Rail Transit,”
Transportation Research Board, Final Report for TCRP Project D-12, December 2009.
46
J.T. Nelson, H.J. Saurenman, G.P. Wilson, “Handbook of Urban Rail Noise and Vibration Control,” prepared
under contract to U.S./DOT Transportation Systems Center, Report No. UMTA-MA-06-0099-82-2, February
1982.
47
International Organization for Standardization, “Mechanical Vibration – Ground-borne Noise and Vibration
Arising from Rail Systems,” ISO/FDIS 14837-1:2005.
48
Institute of Environmental Sciences and Technology, “Considerations in Clean Room Design,” RR-CC012. 3,
2015.
49
U.S. Department of Transportation, Volpe National Transportation Systems Center, “Vibration
Characteristics of the Transrapid TR08 Maglev System,” Report No. DOT-VNTSC-FRA-02-06, March 2002.
50
S. McKenna, “A Study of Build Amplification from Ground-Borne Vibration,” Noise-Con 2011, Portland,
O
regon, July 25-27, 2011
.
51
American National Standards Institute, “Acoustical Terminology,” ANSI S1.1-1994.
52
J.T. Nelson, H.J. Saurenman, "A Prediction Procedure for Rail Transportation Ground-Borne Noise and
Vibration," Transportation Research Record, 1143, August 1988.
FEDERAL TRANSIT ADMINISTRATION 241
53
J. T. Nelson, "Tri-Met Track Vibration Isolation Tests," Final Report for Portland Tri-Met, October 1998.
54
J.T. Nelson, H.J. Saurenman, "Ground-Borne Vibration Tests with MARTA C-Car," report prepared for
Metropolitan Atlanta Rapid Transit Authority, November 16, 1981.
55
H.J. Saurenman, "Preliminary Results of Ground-Borne Vibration Tests with BRRT/Miami Vehicle," technical
memorandum prepared for US DOT/Transportation Systems Center, contract DOT-TSC-1796, 8
February1983.
56
H.J. Saurenman, "Ground-borne Vibration Tests with NFTA Prototype Vehicle at the Transportation Test
Center," technical memorandum prepared for Transportation Test Center, Project No. P-83-C-01078, 3
August 1983.
57
H.J. Saurenman, "Noise and Vibration Tests with Portland Tri-Met Prototype Vehicle at the Transportation
Test Center," technical memorandum prepared for Transportation Test Center, Project No. P-83-C-02649,
26 March 1984.
58
R.A. Carman, D.L. Watry, “Measured Vibration Reduction Performance of Ballast Mat Installation for Light Rail
Vehicles on Embedded Track,” APTA, 1997 Rapid Transit Conference of the APTA, V. 3-Way & Structures
and Construction (1997-8).
59
D.A. Towers, “Evaluation of the Ground-Borne Vibration Reduction Properties of Tire Derived Aggregate
I
nstalled on the Denver RTD Light Rail System,” Harris Miller Miller and Hanson Inc., 2012
.
60
F. E. Richert, J. R. Hall, Vibrations of Soils and Foundations, Prentice-Hall, Inc., Englewood
Cliffs, NJ, 1970.
61
U.S. Environmental Protection Agency, "Noise from Construction Equipment and Operations, Building
Equipment and Home Appliances," NTID300.1, 31 December 1971.
62
Society of Automotive Engineers, "Exterior Sound Level Measurement Procedure for Powered
Mobile Construction Equipment," SAE Recommended Practice J88a, 1976.
63
Society of Automotive Engineers, "Sound Levels for Engine Powered Equipment," SAE Standard J952b, 1976.
64
U.S. Department of Transportation, Federal Highway Administration, “FHWA Roadway Construction Noise
Model User’s Guide,” FHWA-HEP-05-054, January 2006. Available at
http://www.fhwa.dot.gov/environment/noise/construction_noise/rcnm/.
65
E. Thalheimer, “Construction noise control program and mitigation strategy at the Central Artery/Tunnel
P
roject,” Noise Control Eng. J. 48(5), September–October 2000, 157-165)
.
66
U.S. Department of Transportation, Federal Highway Administration. “Highway Construction
Noise Handbook,” FHWA-HEP-06-015, August 2006.
67
D.J. Martin, "Ground Vibrations from Impact Pile Driving during Road Construction," Supplementary Report
5
44, United Kingdom Department of the Environment, Department of Transport, Transport and Ro
ad
Rese
arch Laboratory,
1980.
68
J.F. Wiss, "Vibrations during Construction Operations," Journal of Construction Division, Proc.
American Society of Civil Engineers, 100, No. CO3, 239-246, September 1974.
69
J.F. Wiss, "Damage Effects of Pile Driving Vibrations," Highway Research Record, No. 155, Highway Research
Board, 1967.
FEDERAL TRANSIT ADMINISTRATION 242
70
D.A. Towers, "Ground-borne Vibration from Slurry Wall Trench Excavation for the Central Artery/Tunnel
P
roject Using Hydromill Technology," Proc. InterNoise 95, Newport Beach, CA, July 19
95.
71
Swiss Consultants for Road Construction Association, "Effects of Vibration on Construction," VSS-SN640-312a,
Zurich, Switzerland, April 1992.
72
American Public Transportation Association, Public Transportation Factbook, 55th Edition, March 2004.
73
American National Standards Institute, “Preferred Frequencies, Frequency Levels and Band Numbers for
Acoustical Measurements,” ANSI S1.6-1984 (R2006).
74
U.S. Environmental Protection Agency, “Information on Levels of Environmental Noise Requisite to Protect
Public Health and Welfare with an Adequate Margin of Safety,” EPA Report No. 550/9-74-004, March 1974.
75
National Academy of Sciences, “Guidelines for Preparing Environmental Impact Statements on Noise,” Report
from Committee on Bioacoustics and Biomechanics (CHABA) Working Group 69, February 1977.
76
American Public Transit Association, “Noise and Vibration,” 1981 Guidelines for Design of Rapid Transit
Facilities, Section 2.7, 1981.
77
T.J. Schultz, “Synthesis of Social Surveys on Noise Annoyance,” Journal of the Acoustical Society of America, Vol.
64, No. 2, August 1978, 377-405.
FEDERAL TRANSIT ADMINISTRATION 243
FEDERAL TRANSIT ADMINISTRATION a
FEDERAL TRANSIT ADMINISTRATION 128
U.S. Department of Transportation
Federal Transit Administration
East Building
1200 New Jersey Avenue, SE
Washington, DC 20590
http://www.fta.dot.gov/research
U.S. Department of Transportation
Federal Transit Administration
East Building
1200 New Jersey Avenue, SE
Washington, DC 20590
https://www.transit.dot.gov/about/research-innovation
