TABLE OF CONTENTS
SECTION

PAGE

1.

INTRODUCTION ..............................................................................................................1
1.1 Study Background ........................................................................................... 1
1.2 Build Alternative .............................................................................................. 2
1.2.1 Build Alternative, 2-Lane Option ........................................................... 6
1.2.2 Build Alternative, 4-Lane Option ........................................................... 6
1.2.3 Unresolved Issues ................................................................................ 6
1.3 Overview of Noise and Vibration Assessment Approach .............................. 12
1.4 Noise and Vibration Sources Associated with LRT Systems......................... 13
1.5 Summary of Noise and Vibration Impact Analysis ......................................... 15

2.

AFFECTED ENVIRONMENT........................................................................................ 17
2.1 Existing Conditions – Noise........................................................................... 17
2.2 Existing Conditions – Vibration...................................................................... 20
2.2.1 Vibration Propagation Test Procedure................................................ 21
2.2.2 Vibration Propagation Test Sites ........................................................ 22
2.2.3 Results of Vibration Propagation Tests .............................................. 27

3.

REGULATORY FRAMEWORK .................................................................................... 32
3.1 State and Local Noise and Vibration Limits ................................................... 32
3.2 FTA Noise Impact Criteria ............................................................................. 32
3.3 City of Mesa Limits on Construction Noise .................................................... 36
3.4 FTA Vibration Impact Criteria ........................................................................ 36

4.

NOISE AND VIBRATION METHODOLOGY ................................................................ 41
4.1 Noise and Vibration Assessment Approach .................................................. 41
4.2 Noise Prediction Models................................................................................ 42
4.2.1 Prediction Model, Noise from Light Rail Vehicle Operations .............. 42
4.2.2 Prediction model, Noise from Audible Warnings ................................ 44
4.2.3 Prediction Model, Ancillary Equipment ............................................... 45
4.3 Vibration Prediction Model ............................................................................ 45

5.

NOISE AND VIBRATION IMPACT ASSESSMENT ..................................................... 51
5.1 LRT Related Noise ........................................................................................ 51
5.1.1 Operational Noise ............................................................................... 51
5.1.2 Audible Warnings at Grade Crossings................................................ 54
5.1.3 Ancillary Equipment ............................................................................ 58
5.2 Operational Vibration .................................................................................... 59
5.3 Construction Noise and Vibration .................................................................. 67
5.3.1 Construction Noise ............................................................................. 67
5.3.2 Construction Vibration ........................................................................ 68

6.

MITIGATION OPTIONS ................................................................................................ 70

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6.1
6.2
6.3
6.4
6.5
6.6
7.

Train Noise .................................................................................................... 70
Audible Warnings .......................................................................................... 70
Transit Power Substations ............................................................................ 70
Train Vibration ............................................................................................... 70
Construction Noise ........................................................................................ 73
Construction Vibration ................................................................................... 74

REFERENCES .............................................................................................................. 76

APPENDIX A: FUNDAMENTALS OF NOISE AND VIBRATION ........................................ A-1
A.1 Noise Fundamentals .................................................................................... A-1
A.2 Vibration Fundamentals ............................................................................... A-3
APPENDIX B: VIBRATION MEASUREMENT RESULTS ................................................... B-1
B.3 Detailed Results from Vibration Propagation Tests ...................................... B-1
B.4 Comparison of Predicted Vibration Spectra ................................................. B-6
APPENDIX C: FORCE DENSITY MEASUREMENTS ........................................................C-1
C.5 Transfer Mobility Measurements ................................................................. C-1
C.6 METRO Train Vibration Measurements ...................................................... C-3
C.7 Force Density Calculations.......................................................................... C-4
APPENDIX D: METRO LRV NOISE MEASUREMENT RESULTS ....................................D-1
D.8 LRV Noise Measurements: METRO Revenue Service ............................... D-1
D.9 LRV Noise Measurements: Test Train ........................................................ D-4
APPENDIX E: CLUSTER LOCATIONS ............................................................................... E-1
APPENDIX F: DRAFT NOISE MEASUREMENT REPORT FOR CENTRAL MESA LRT
EXTENSION .......................................................................................................................... F-1

LIST OF FIGURES
Figure 1: Central Mesa Study Area ................................................................................. 1
Figure 2: Locally Preferred Alternative ............................................................................ 3
Figure 3: Build Alternative, Sycamore To Country CLub Drive........................................ 7
Figure 4: Build Alternative, 2-Lane Option Country Club Drive to Hobson ...................... 9
Figure 5: Build ALternative, 4-Lane Option Country Club Drive To Hobson .................. 11
Figure 6: Aerial view of Existing Noise Test Sites ......................................................... 19
Figure 7: Schematic of Vibration Propagation Test ....................................................... 22
Figure 8: Locations of Vibration Propagation Test Sites................................................ 24
Figure 9: Site V1, East Valley Institute ot Technology ................................................... 25
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Figure 10: Site V2, Epernay Apartment Complex .......................................................... 25
Figure 11: Site V3, Downtown Mesa ............................................................................. 26
Figure 12: Site V4, Mesa Arts Center ............................................................................ 26
Figure 13: Measured LSTM and Coherence, Site V1 .................................................... 28
Figure 14: Measured LSTM and Coherence, Site V2 .................................................... 29
Figure 15: Measured LSTM and Coherence, Site V3 .................................................... 30
Figure 16: Measured LSTM and Coherence, Site V4 .................................................... 31
Figure 17: FTA Noise Impact Criteria ............................................................................ 34
Figure 18: FTA Criteria for Detailed Vibration Analysis ................................................. 39
Figure 19: LRT Sound Levels vs Distance from Track Centerline ................................. 43
Figure 20: METRO LRT Force Density at 15 and 25 mph............................................. 47
Figure 21: Predicted LRV Vibration Spectrum at 33 mph .............................................. 47
Figure 22: Predicted LRV Vibration Spectrum at 29 mph .............................................. 48
Figure 23: Predicted LRV Vibration Spectrum at 22 mph .............................................. 48
Figure 24: Predicted Overall Vibration versus Distance ................................................ 49
Figure 25: Ikeda Theater Measurement Position .......................................................... 63
Figure 26: Measurement Position, Box Office Lobby .................................................... 63
Figure 27: Measured LSTM and Coherence at The Mesa Arts Center ......................... 64
Figure 28: Predicted Vibration at The Mesa Arts center ................................................ 65
Figure 29: FTA Criteria and Predicted Vibration for EVIT Health Sciences Building ..... 67
Figure 30: Performance of Different Vibration Mitigation Measures ............................. 72
Figure A-1: Typical Outdoor and Indoor Noise Levels ................................................. A-3
Figure A-2: Typical Vibration Levels ............................................................................ A-5
Figure B-1: Vibration Propagation Site V1................................................................... B-1
Figure B-2: Vibration Propagation Site V2................................................................... B-2
Figure B-3: Vibration Propagation Site V3................................................................... B-2
Figure B-4: Vibration Propagation Site V4 in Front of Mesa Center ............................ B-3
Figure B-5: Comparison of Predicted Vibration at 33 mph for all Four measurement
Sites ....................................................................................................... B-6
Figure B-6: Comparison of Predicted Vibration at 29 mph for all Four measurement
Sites ....................................................................................................... B-7
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Figure B-7: Comparison of Predicted Vibration at 22 mph for all Four measurement
Sites ....................................................................................................... B-8
Figure C-1: Aerial View of FDL Measurement Location .............................................. C-1
Figure C-2: Impact Testing, Eastbound Track ............................................................. C-2
Figure C-3: LSTM and Coherence for FDL Test ......................................................... C-2
Figure C-4: Test Train Passby for FDL Measurement ................................................. C-3
Figure C-5: Measured Test Train Vibration ................................................................. C-4
Figure C-6: Force Density level of METRO Starter Line, 5 to 30 mph ......................... C-6
Figure C-7: Force Density level of METRO Starter Line, 35 and 40 mph .................... C-7
Figure C-8: METRO LRV Force Density levels versus Speed .................................... C-7
Figure D-1: Aerial View of Microphone Locations for LRT Noise Measurements ........ D-1
Figure D-2: Measured Revenue Train Passby Noise, 50 ft ......................................... D-2
Figure D-3: Measured Revenue Train Passby Noise, 100 ft ....................................... D-3
Figure D-4: Measured Average Revenue Train Noise................................................. D-4
Figure E-1: Clusters sheet 1 ........................................................................................ E-2
Figure E-2: Clusters sheet 2 ........................................................................................ E-3
Figure E-3: Clusters sheet 3 ........................................................................................ E-4
Figure E-4: Clusters Sheet 4, 2-Lane Alternative ........................................................ E-5
Figure E-5: Clusters Sheet 5, 2-Lane Alternative ........................................................ E-6
Figure E-6: Clusters Sheet 4, 4-Lane Alternative ........................................................ E-7
Figure E-7: Clusters sheet 5, 4-Lane Alternative ......................................................... E-8
Figure F-1: Summary of Hourly Leq of Long Term Noise Measurements .................... F-1

LIST OF TABLES
Table 1: LRT Operation Plans ......................................................................................... 3
Table 2: Stations, transit Centers, and Park-and-Rides .................................................. 5
Table 3: Summary of Operational Noise Impact and Mitigation .................................... 16
Table 4: Summary of Vibration Impact and Mitigation ................................................... 16
Table 5: Summary of Existing Noise Measurements ..................................................... 20
Table 6: FTA Land Use Categories and Noise metrics ................................................. 33
Table 7: FTA Noise Impact Criteria ............................................................................... 35
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Table 8: FTA Impact Thresholds for Groundborne Vibration General Impact Assessment
................................................................................................................. 37
Table 9: Interpretation of Vibration Criteria for Detailed Analysis .................................. 40
Table 10: Groundborne Noise and Vibration Impact Criteria for Special Buildings ....... 40
Table 11: Summary of Noise Impact Assessment For Category 2 ................................ 53
Table 12: Summary of Noise Impact Assessment for Category 3 ................................. 54
Table 13: Summary of Noise Impact Assessment for Category 1 ................................. 54
Table 14: LRT Bell Noise Impacts at Category 2 Receivers.......................................... 56
Table 15: LRT Bell Noise Impacts at Category 3 Receivers.......................................... 57
Table 16: LRT Bell Noise Impacts at Category 1 Receivers.......................................... 57
Table 17: Predicted TPSS Noise ................................................................................... 59
Table 18: Summary of Vibration Impact Assessment for Category 2 ............................ 61
Table 19: SUmmary of Vibration Impact Assessment for Category 3 ........................... 62
Table 20: Predicted Groundborne Noise and Vibration, Mesa Arts Center ................... 65
Table 21: Construction Noise Guidelines ...................................................................... 68
Table 22: Predicted Construction Noise ........................................................................ 68
Table 23: Construction Vibration Limits ......................................................................... 69
Table 24: Summary of Vibration Mitigation.................................................................... 73
Table B-1: Line Source Transfer Mobility Coefficients, Site V1 ................................... B-4
Table B-2: Line Source Transfer Mobility Coefficients, Site V2 ................................... B-4
Table B-3: Line Source Transfer Mobility Coefficients, Site V3 ................................... B-5
Table B-4: Line Source Transfer Mobility Coefficients, Site V4 ................................... B-5
Table D-1: Summary of Noise Measurements of All Test Train Passbys .................... D-5
Table D-2: Average Test Train Noise .......................................................................... D-5
Table F-1: Results of Measured Hourly Leq at Long-term Noise Measurement Sites .. F-2

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1.

INTRODUCTION

This noise and vibration technical report is prepared to support the Environmental
Assessment (EA) for high capacity transit improvements being considered in the study
area for the Central Mesa Light Rail Transit (LRT) Extension. This chapter begins with a
short background of the study and a description of the alternatives being considered in
the EA.
1.1

STUDY BACKGROUND

The Central Mesa Extension study area is bounded on the west by the Light Rail Starter
Line’s eastern terminus at Sycamore/Main Street; University Drive to the north; Power
Road to the east; and the Superstition Freeway (U.S. 60) on the south (Figure 1).
FIGURE 1: CENTRAL MESA STUDY AREA

Source: METRO (2009).

A two-tiered alternatives development process was implemented to evaluate the Central
Mesa Study Area conceptual alternatives. The first phase (Tier 1) included a conceptual
level evaluation that analyzed the advantages and disadvantages of the initial list of
potential alternatives to address the transportation needs of the study area (see
separate Tier 1 Evaluation of Alternatives Report, October 2007, for more information).
The initial alternatives considered both LRT and bus rapid transit (BRT) modes.
All alternatives began at the eastern terminus of the recently opened LRT Starter Line
Station at Sycamore/Main Street and extended east to the Superstition Springs Center
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area via Main Street (with 1st Street and 1st Avenue suboptions downtown) and Power
Road. Fixed guideway (via LRT or BRT) generally extended east to about Horne
(between Mesa and Stapley Drives) with BRT offering limited stop express service
further east in existing travel lanes (similar to Valley Metro Link) to Superstition Springs
Center. LRT consisted of a dedicated fixed guideway with two tracks (one track in each
direction) that ran mostly in the middle of the existing street system. BRT also had a
dedicated fixed guideway for a portion of the project as previously mentioned. The initial
alternatives were subject to a “fatal flaw’ screening at the Tier 1 phase; the most
feasible alternatives were identified and retained for further analysis, and the
alternatives deemed unresponsive to Tier 1 evaluation criteria were eliminated from
continued study.
The alternatives that remained after the Tier 1 analysis and public, agency, and other
stakeholder input were then subjected to a more detailed evaluation (Tier 2). The Tier 2
evaluation continued to consider both LRT and BRT build alternatives. The criteria
developed to analyze all of the build alternatives in Tier 2 began to quantify ridership
potential, capital and operating and maintenance costs, land use and economic
development impacts, traffic issues, environmental factors, conceptual engineering, and
public preferences. See the complete Tier 2 Evaluation of Alternatives Report,
December 2008, which defines the Tier 2 alternatives considered and details the results
of the evaluation.
Based on the results of the Tier 2 evaluation, public meetings, and agency and other
stakeholder input, the recommended build alternative is to advance LRT as the
preferred technology and Main Street as the preferred alignment. The locally preferred
alternative (LPA) includes a light rail extension on Main Street east to an interim end-ofthe-line near Mesa Drive as Phase 1. See the complete Recommended Alternative
Report, Draft June 2009 for discussion of the rationale for selection of the LPA. The
Phase 1 project is scheduled to begin operations in 2016 and is the major focus of the
EA being prepared pursuant to the National Environmental Policy Act (NEPA). The NoBuild Alternative will also continue to be considered as specified by NEPA. The Phase 1
project connects logical termini and has independent utility meaning that the project is a
reasonable expenditure even if no additional transportation improvements are made in
the area.
1.2

BUILD ALTERNATIVE

The LRT Main Street Alternative was selected as the recommended LPA for more
detailed analysis in the EA. This LPA recommendation was approved by the City of
Mesa City Council (May 2009) and the METRO Board of Directors (June 2009). The
LPA has two design options for Main Street in the area east of Country Club Drive: 1) 2
Lanes; and 2) 4 Lanes. The design options are described at the end of this discussion.
Whether to implement the Build Alternative, 2-Lane Option or the Build Alternative, 4Lane Option will be decided after completion of a series of public workshops, the Draft
EA, and receipt of input during the Draft EA public comment period.
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The Build Alternative, or LPA, is shown in Figure 2. The Build Alternative includes a
double-track LRT guideway that would operate along the middle of Main Street from just
east of Sycamore to just east of Mesa Drive, a distance of 3.1 miles. LRT is electrically
powered and receives its power from overhead power lines within the street right-ofway. LRT operations would include a traffic signal priority system (predictive priority), to
allow for faster travel times. The light rail vehicles will be the same as the ones currently
being used for the LRT Starter Line. Major operating plan features are listed in Table 1.
TABLE 1: LRT OPERATION PLANS
Headways
Number of Vehicles

Line-haul Capacity
Hours of Operation

All day except late evening:
10 minutes
Late evening:
20 minutes
6 – Central Mesa LRT Extension
50 – LRT Starter Line and Northwest LRT
56 – Total fleet
2,700 passengers per peak hour per direction
(Based on 3 vehicles per train and 150 passengers/vehicle)
Daily = ~20 hours

FIGURE 2: LOCALLY PREFERRED ALTERNATIVE

This alternative is an extension of the LRT Starter Line that opened in December 2008
and would provide a seamless connection (no transfer required) from the current
eastern terminus of the LRT Starter Line at Sycamore and continues east to just east of
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Mesa Drive. Tail tracks would continue east of the station platform to a point
approximately 425 feet east of Hobson.
East of Center Street to Superstition Springs Center (near Power Road/US 60), the
existing Valley Metro LINK BRT would connect to LRT and operate in mixed traffic as it
does today as a skip-stop express service. As a result of the Build Alternative, Valley
Metro LINK BRT service would be discontinued along Main Street between Sycamore
and Center Street to eliminate service duplication, and its operational frequency in the
off-peak will increase from 30 to 15 minutes. However, service during peak periods will
remain the same as today (15 minutes). Other than that, no other changes to the LINK
operations or facilities will be necessary for the Phase 1 LRT extension being evaluated
in the EA. LRT stations/LINK BRT stops, bus interface locations, and park-and-ride
locations are identified in Table 2. A new bus interface location would be constructed
by the City of Mesa as part of a separate project in the downtown area. A new parkand-ride facility would be built near the end-of-line LRT station at Mesa Drive. The
facility would encompass two sites at the Main Street/Lesueur intersection: 1)
northwest quadrant; and 2) southwest quadrant.
Also recommended as funding becomes available is a future (Phase 2) extension of
LRT to Gilbert Road. This extension would provide enhanced regional transit
connections and opportunity for a larger regional park-and-ride facility. At this time,
Phase 2 is not identified in the MAG Regional Transportation Plan (RTP) and is not
evaluated in the EA. However, the Phase 2 recommendation has been forwarded to
MAG and has been identified as an “illustrative project” for inclusion in the RTP. Should
the Phase 2 project move forward, it will be subject to NEPA compliance.
Construction of the Build Alternative would include installation of trackwork, an
overhead contact system (OCS) for the distribution of electricity to LRT vehicles,
traction power substations, and signaling and communication systems. The LRT
transitway would consist of tracks formed of continuously welded rails. The rails would
be embedded track supported on a concrete slab.
The OCS would consist of steel or concrete poles installed along the operating right-ofway to support the electrical power line. Poles would be about 25 feet tall and typically
installed at intervals from 90 to 170 feet. The OCS would be designed to be compatible
with visual and aesthetic characteristics of the corridor. The poles would generally be
located in the center of the two tracks, wherever possible. In some locations, catenary
poles may be located on the side of the LRT trackway with the overhead electrical line
suspended over the LRT tracks.
Electricity for LRT operations would be supplied to the OCS from traction power
substations (TPSS) located along the proposed LRT alignment. These electrical
substations would be enclosed structures approximately 20-by-40 feet (30-by-60 feet
including the grounding mat around the substation) located proximally to the LRT
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alignment. One TPSS would be required for roughly each mile of track. Specific
locations will be determined as design is further refined.
TABLE 2: STATIONS, TRANSIT CENTERS, AND PARK-AND-RIDES
Station/Stop
LRT Facilities (Stations)
Sycamore/Main St.
(LRT Starter Line End-of-Line
Station)
Alma School/Main St.

Type of
Station

Park-andRide

Bus
Interface

Yes

Yes

Regional

Location/
Platform Configuration

East of intersection
Center platform
Facility not attributable to LRT extension
Community
No
No
West of intersection
Center platform
Country Club/Main St.
Regional
No
No
East of intersection
Center platform
Centennial/Main St.
Community
No
Yes
West of intersection
Center platform
Bus Facility is a separate project and is
not attributable to LRT extension
Mesa/Main St.
Community
Yes
No
Station—East of intersection
Station—Center platform
Park-and-Ride—2 sites (northwest and
southwest quadrants of Lesueur/Main
intersection)
Valley Metro Link BRT Facilities (Existing Stops—Facilities not attributable to LRT extension)
1
Stapley/Main St.
Neighborhood
No
No
East of intersection
Gilbert/Main St.1
Neighborhood
No
No
West/east of intersection
Lindsay/Main St.1
Neighborhood
No
No
East of intersection
Val Vista/Main St.1
Neighborhood
No
No
West/east of intersection
Greenfield/Main St.1
Neighborhood
No
No
West/east of intersection
Higley/Main St.1
Neighborhood
No
No
East of intersection
Recker/Main St.1
Neighborhood
No
No
West/east of intersection
Power/Main St.1
Community
No
No
West of intersection
Broadway/Power1
Community
No
No
North of intersection
Regional
Yes
Yes
North of intersection
U.S. 60/Power (Superstition
1
Springs Center)
1Station locations as part of existing Valley Metro LINK BRT project. Station locations and amenities would remain.
Source: METRO (2009).

LRT vehicles for the Central Mesa Extension would be maintained and serviced at the
existing LRT Starter Line Operations and Maintenance Center (OMC), located south of
Washington Street between State Route (SR) 143 and Loop 202. The OMC will have
sufficient capacity to service LRT vehicles allocated to the Central Mesa LRT Extension,
and no additional facility will be required.
The existing traffic lane capacity along Main Street would be maintained between
Sycamore and Country Club Drive. Typical cross sections are presented in Figure 3.
For the segment east of Country Club Drive to the LRT eastern terminus near Mesa
Drive, two design options are being considered:
x

Build Alternative, 2-Lane Option

x

Build Alternative, 4-Lane Option

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These design options are further described below.
1.2.1 Build Alternative, 2-Lane Option
Main Street’s traffic lane capacity would be reduced from two lanes in each direction to
one lane in each direction from Country Club Drive to Hobson. Acquisition of additional
right-of-way along the alignment would be minimal to accommodate the fixed guideway
as a result of the reduction of travel lanes. Typical cross sections at various locations
along the Build Alternative, 2-Lane Option are shown in Figure 4. The station, park-andride, and bus interface facility locations shown in Table 2 apply to the 2-Lane Option.
1.2.2 Build Alternative, 4-Lane Option
Main Street’s traffic lane capacity would be maintained from Country Club Drive to
Hobson. Acquisition of additional right-of-way would be required to accommodate the
fixed guideway as a result of maintaining the existing numbers of lanes. Typical cross
sections at various locations along the Build Alternative, 4-Lane Option are shown in
Figure 5. All of the station, park-and-ride, and bus interface facility locations are as
illustrated in Table 2.
1.2.3 Unresolved Issues
Several issues remain to be decided and will be further considered as the EA proceeds
and community outreach continues. In addition to the previously discussed optional
traffic design configurations downtown, decisions will need to be made about the
following:
x On-street parking
x Bicycle facilities
x TPSS location
x OCS
x Left turn requirements
x Pedestrian access points
x Park-and-ride sizing, layout and capacity
x Station design
x Urban design/public art
x Refinement of utilities and location
x Construction staging

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FIGURE 3: BUILD ALTERNATIVE, SYCAMORE TO COUNTRY CLUB DRIVE

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FIGURE 3: BUILD ALTERNATIVE, SYCAMORE TO COUNTRY CLUB DRIVE
(continued)

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FIGURE 4: BUILD ALTERNATIVE, 2-LANE OPTION COUNTRY CLUB DRIVE TO
HOBSON

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FIGURE 4: BUILD ALTERNATIVE, 2-LANE OPTION COUNTRY CLUB DRIVE TO
HOBSON (continued)

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FIGURE 5: BUILD ALTERNATIVE, 4-LANE OPTION COUNTRY CLUB DRIVE TO
HOBSON

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1.3

OVERVIEW OF NOISE AND VIBRATION ASSESSMENT APPROACH

The noise and vibration impact assessment has followed the guidelines provided in the
Federal Transit Administration (FTA) manual Transit Noise and Vibration Impact
Assessment (Ref. 1). This section summarizes the approach used. Additional
information on the assessment may be found in Chapter 4, Noise and Vibration
Methodology. The general approach is:
x

Identify potential sources of noise and vibration.

x

Determine existing noise and vibration conditions through measurements at
representative locations. The vibration measurements include testing to
determine how efficiently vibration would be transmitted from the tracks, through
the ground, and into building foundations.

x

Group all potentially affected sensitive receptors into clusters. The LRT tracks
would be approximately the same distance from the sensitive buildings in each
cluster and the clusters are small enough that train speeds and other operating
parameters are the same for all land uses in the cluster. The locations of the
clusters and buildings included in each cluster are shown in Appendix E.

x

Develop prediction models for each source.

x

Determine impact thresholds at each cluster.

x

Use prediction models to estimate future noise and vibration levels at each
cluster.

x

Compare the predicted noise and vibration levels to the impact thresholds.
Where predicted levels exceed the applicable impact thresholds, evaluate
mitigation options.

Note that historic properties have been identified along the alignment. There is one
building listed on the National Register of Historic Places (NRHP), the Landmark
Restaurant at the southwest corner of Main Street and Extension. There also is one
historic district, the Temple Historic District, that is listed and is composed of numerous
houses and the Mormon Temple which are not individually listed but are contributing
properties to the significance of the district. In addition, there are 34 “recommended as
eligible” historic buildings and objects (signs) identified within the project corridor. Most
of the other individually eligible buildings are commercial in nature as well as two
houses and one hotel. The eligible signs are associated with commercial uses. The
historic structures do not appear to be unusually sensitive to vibration. In all cases, the
predicted levels of light rail vehicle (LRV) vibration are well below the thresholds used to
protect the most sensitive and fragile structures from damage. Potential for noise and
vibration from light rail operations to be annoying to occupants of historic structures has
been based on the appropriate noise and vibration impact criteria for the current use of
the building. The noise and vibration analysis indicates no impacts on any listed or
potentially eligible historic properties.
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There is some potential for damage to historic structures during construction of the Build
Alternative. As discussed in Section 6 (Mitigation), the potential for damage can be
minimized through a preconstruction survey of the historic structures to identify preexisting conditions and determine if any special measures are warranted to minimize
the potential for damage to these structures. The survey can be limited to the first row
along Main Street and potentially fragile historic resources located within approximately
200 ft of Main Street.
1.4

NOISE AND VIBRATION SOURCES ASSOCIATED WITH LRT SYSTEMS

Following is a summary of the most significant noise and vibration sources associated
with operating light rail systems. Additional information may be found in Chapter 4,
Noise and Vibration Methodology.
x

Light Rail Vehicle Operations: This is the normal noise from the operation of
LRVs and includes noise from steel wheels rolling on steel rails (wheel/rail noise)
and from propulsion motors, air conditioning, and other auxiliary equipment on
the vehicles. As expected, the wheel/rail noise increases with speed. At speeds
greater than 20 mph, the wheel/rail noise usually dominates noise from the
vehicle auxiliary equipment. Train operations also create groundborne vibration
that may be intrusive to occupants of buildings when the tracks are relatively
close to buildings. In all cases, the vibration generated by light rail operations is
expected to be well below what would be required to cause even minor cosmetic
damage to the building.

x

Traffic Noise: Because LRT would share the right-of-way with vehicular traffic
on Main Street, the proposed project would result in changes in traffic patterns
and volumes on Main Street and intersecting major arterials such as Alma
School Road and Country Club Road. In all cases, the forecasted change in
traffic volume on Main Street and its intersections is insufficient to cause more
than a 1 dB change in sound levels. Although there are a few proposed property
acquisitions for additional right-of-way along the alignment for the Build
Alternatives, the acquisitions would not alter the existing acoustic shielding for
any noise sensitive receivers. Therefore, a detailed assessment of impacts from
traffic noise has not been performed as part of this study.

x

Audible Warnings: Train movements at all intersections will be controlled by
transit-priority signals that are synchronized with Main Street traffic lights. There
will be no at-grade crossings where gates are required. The Valley Metro Rail
LRVs have two audible warning sounds, a horn and a bell. The horn is used at
the operator’s discretion as a warning to pedestrians and motorists when there is
a potential safety issue. The horns on the current LRT Starter Line LRVs are set
to generate a minimum sound level of 102 dBA at 100 feet (ft) in front of the
LRVs. The bells are set to generate a minimum sound level of 80 dBA at 50 ft in
front of the LRVs and are set to operate simultaneously at both ends of the lead
vehicle and the rear of the trailing vehicle. Because horns would only be used for

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emergencies, they would be an insignificant noise source and a detailed
assessment of horn noise has not been performed as part of this study. With
regard to bells, train operators will ring the bell twice before accelerating from any
stop and when approaching a crowded station. A reasonable assumption is that
approximately half of the trains would sound the bell at stoplights. All trains would
sound the bell when entering and exiting stations. The potential impacts of the
combined noise from the bells and trains are included in the noise assessment.
x

Station Public Address System: Public Address (PA) systems will be installed
at the stations to announce when trains are arriving at the stations and to provide
other information to patrons. These systems will have automatic volume controls
that are designed so the announcements will be only a few decibels above
ambient noise levels. With proper design of the public address systems and the
automatic volume control, the noise from the PA system should not generate any
adverse impacts in communities near the stations.

x

Special Trackwork: The Central Mesa LRT Extension Project will be
constructed of continuously welded track, which means that the “clickety-clack”
noise associated with older rail systems is eliminated. The one exception is at
special trackwork for turnouts and crossovers where two rails must cross. A
fixture referred to as a “frog” is used where rails must cross. The wheel impacts
at the gaps in the rails of a standard frog cause noise levels near special
trackwork to increase by approximately 6 dB and groundborne vibration near
special trackwork to increase by approximately 10 dB. Noise and vibration from
special trackwork is covered in this study.

x

Wheel Squeal: Wheel squeal may be generated when steel-wheel transit
vehicles traverse tight radius curves. It is very difficult to predict when and where
wheel squeal will occur. A general guideline is that there is potential for wheel
squeal at any curve with a radius that is less than 600 ft. For the Central Mesa
LRT Extension no wheel squeal is anticipated because there are no sharp curves
and the entire alignment is on tangent (straight) track along Main Street.

x

Ancillary Equipment: Transit power substations (TPSS) are the only ancillary
equipment associated with the proposed project with potential for creating noise
impact. The ventilation fans provided at each substation are the dominant noise
source of most TPSS units. There would be three TPSS units distributed along
the proposed project. At present, seven potential sites have been identified for
the three TPSS units. Several of the potential sites are adjacent to residential
land uses. Noise impacts from TPSS units at all the potential sites are covered in
this study. The locations of the TPSS units will be finalized at later stages of the
project and all noise producing equipment will be reviewed during the design
process to ensure that it will be placed in an appropriate location where noise
impacts will be minimized.

x

Construction Noise and Vibration: All the sources discussed above are
associated with operation of the proposed project. Similar to any other major

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infrastructure project, construction would require use of heavy equipment that
generates relatively high noise and vibration levels.

1.5

SUMMARY OF NOISE AND VIBRATION IMPACT ANALYSIS

This section is an overview summary of the noise and vibration impact assessment for
the Central Mesa LRT Extension project. The results of the noise analysis presented in
Table 3 show that:
x

Predicted noise from LRT operations does not exceed the applicable FTA noise
impact threshold at any sensitive receiver.

x

Noise from audible warnings is not predicted to exceed the applicable impact
threshold at any sensitive receiver.

x

Seven optional locations for TPSS are currently under consideration for siting of
a total of three TPSSs that will be needed to power the LRVs along the
alignment. One of the potential TPSS locations could result in noise impacts at
sensitive receivers. However, all of the potential impacts from TPSS noise can be
mitigated through straightforward measures such as locating the unit so that the
ventilation fans face away from the closest residences.

The vibration results summarized in Table 4 show that:
x

Groundborne vibration from train operations is predicted to exceed the FTA
impact threshold at several second floor units of three motels and at two mobile
home parks and a trailer park.

x

All groundborne vibration impacts at the motels can be mitigated by stiffening the
floors of the affected second floor units. Other options for mitigating the vibration
impacts are discussed in Chapter 6.

x

All groundborne vibration at the mobile home parks and trailer park can be
mitigated by making sure that the spaces within 60 ft of the near track centerline
are used by RVs or travel trailers that are on pneumatic tires and not by semipermanently located mobile homes supported by temporary footings.

x

Although no groundborne noise and vibration impacts are predicted at the Ikeda
Theater of the Mesa Arts Center, a more detailed evaluation should be
performed during the Final EA or the Preliminary Engineering phase to confirm
these conclusions.

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TABLE 3: SUMMARY OF OPERATIONAL NOISE IMPACT AND MITIGATION
Noise Source

FTA Category for
Sensitive Land Uses

LRT Operations

Audible Warnings

Category 1
Category 2
Category 3
Category 1
Category 2
Category 3

Exceeds FTA
# of
Impact Level Impacted
Units
No
0
No
0
No
0
No
0
No
0
No
0

Mitigation

No
No
No
No
No
No

Notes:
This table summarizes the conclusions of the noise analysis. For details of the noise analysis refer Table 11
through Table 16.

TABLE 4: SUMMARY OF VIBRATION IMPACT AND MITIGATION
Location

Sensitive Receivers
Exceeding FTA Vibration
Impact Thresholda
West of Alma School Road American Executive Inn
Motel Rawls
Between Alma School
Mobile Home Park
Road and Extension Road
Apache West Mobile Village
East of Extension Road

Mesa Royale Trailer Park
Motel 6

No. of
Mitigation Option
Impacted
Unitsb
1c
Stiffen the floors of the affected unit
3c
Stiffen the floors of the affected units
1
Shift the affected mobile home to
60 feet from the near track centerline
1
Shift the affected mobile home to
60 feet from the near track centerline
1
Shift the affected mobile home to
60 feet from the near track centerline
2c
Stiffen the floors of the affected units

Notes:
a. Sensitive receivers with predicted vibration exceeding the FTA Detailed Impact Criteria.
b. Number of impact units is an estimate of the dwelling units where predicted vibration levels without mitigation
exceed the impact threshold.
c. All the predicted vibration impact is at second floor motel rooms.

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2.

AFFECTED ENVIRONMENT

2.1

EXISTING CONDITIONS – NOISE

The existing ambient noise levels along the project corridor were documented through a
series of noise measurements performed at a number of representative sensitive
receptors.
A logarithmic scale, known as the decibel scale (dB), is used to quantify sound intensity
and compress the scale to a more convenient range. To better approximate the
sensitivity of human hearing, the A-weighted decibel scale has been developed and
abbreviated as “dBA”. Some key metrics of sound are presented here and more details
of sound fundamentals are presented in Appendix A.
Equivalent Sound Level (Leq): The equivalent sound level (Leq) is the most common
means of characterizing community noise. Leq represents a constant sound that, over a
specified period of time, has the same sound energy as the time-varying sound. Leq is
used by FTA to evaluate noise impacts at institutional land uses, such as schools,
churches, and libraries, from proposed transit projects.
Day-Night Sound Level (Ldn): Ldn is basically a 24-hour Leq with an adjustment to
reflect the greater sensitivity of most people to nighttime noise. The adjustment is a
10 dB penalty for all sound that occurs between the hours of 10:00 PM to 7:00 AM. The
effect of the penalty is that, when calculating Ldn, any event that occurs during the
nighttime is equivalent to ten occurrences of the same event during the daytime. Ldn is
the most common measure of total community noise over a 24-hour period and is used
by FTA to evaluate residential noise impacts from proposed transit projects.
LXX: This is the percent of time a sound level is exceeded during the measurement
period. For example, the L99 is the sound level exceeded 99 percent of the
measurement period. For a 1-hour period, L99 is the sound level exceeded for all
except 36 seconds of the hour. L1 represents typical maximum sound levels, L33 is
approximately equal to Leq when free-flowing traffic is the dominant noise source, L50
is the median sound level, and L99 is close to the minimum sound level.
Maximum Sound Level (Lmax): Lmax is the maximum sound level that occurs during
an event such as a train passing. For this analysis Lmax is defined as the maximum
sound level using the slow setting on a standard sound level meter.
Sound Exposure Level (SEL): SEL is a measure of the acoustic energy of an event
such as a train passing. In essence, the acoustic energy of the event is compressed into
a 1-second period. SEL increases as the sound level of the event increases and as the
duration of the event increases. It is often used as an intermediate value in calculating
overall metrics such as Leq and Ldn.
The primary existing noise source along the proposed alignment is vehicular traffic on
Main Street. Noise sensitive receptors along the project corridor include single- and
multi-family residences, motels, hotels, trailer parks, mobile home parks and a number
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of institutional land uses that are used primarily during daytime hours. Institutional land
uses include buildings on the East Valley Institute of Technology (EVIT) campus, the
Landmark Restaurant, the City Hall, a childbirth education class, Tri-City Community
Center, the Pioneer Park and the Mormon Temple. The only special land use where
quiet is an essential element in its intended purpose is the Ikeda Theater (concert hall)
of the Mesa Arts Center.
The noise monitoring to characterize existing noise levels was performed by HDR. The
memorandum prepared by HDR presenting the details of the noise measurements is
attached as Appendix F to this report. The noise measurements consisted of three 24hour noise measurements and six 15-minute noise measurements. An additional 24hour measurement was performed at one site (LT4) in September 2010 to verify the
earlier measurements. The general locations for the measurements are shown in
Figure 6.
In Figure 6, sites LT1, LT2, LT3, and LT4 represent the 24-hour measurements. Sites
M1 through M6 represent the 15-minute tests along the future alignment. These
measurement locations were selected to verify the noise predictions for the Central
Mesa LRT Extension. The measurement results for all locations are summarized in
Table 5. The highest measured Ldn was 71.5 dBA at site LT1, which was located near
the intersection of Main Street and Longmore. The measured Ldn at Site LT3 was
similar at 70.1 dBA. Site LT3 was located at the east end of the project corridor near the
Mormon Temple. The measured Ldn at Site LT2, which was located near the middle of
the corridor was 65.3 dBA. The measured Ldn at LT4, which was located at the Mesa
Arts Center, was 60.6 dBA and was consistent with earlier measurements in the project
area. The noise level at LT4 was significantly lower than the other three sites because
of the larger setback distance of the measurement location from Main Street. For more
explanation of the noise terms used in this chapter, refer to Appendix A, Fundamentals
of Noise and Vibration.
The existing noise levels are an important factor in the noise impact assessment
because the noise impact thresholds are based on the existing noise levels. As
discussed in Appendix A, the higher the levels of existing noise, the more noise that can
be added by the project before the impact threshold is exceeded. For the noise impact
analysis, the measured ambient noise levels were assumed to be representative of
sensitive land uses as follows:
x

LT1: all sensitive land uses between EVIT and Alma School Road

x

LT2 all sensitive land uses from Alma School Road to Mesa Drive

x

LT3: all sensitive land uses east of Mesa Drive.

Thus, LT2 was applied for majority of the Central Mesa LRT Extension project corridor.
In addition to having the lowest Ldn, LT2 has the lowest daytime Leq compared to all
measurement sites between Alma School Road and Mesa Drive. As discussed above,
assuming a lower existing noise level results in lower noise impact thresholds, which is
a conservative approach that ensures no impacts are overlooked.
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FIGUR
RE 6: AERIIAL VIEW OF
O EXISTIN
NG NOISE TEST SITES

Source: HD
DR Inc., Phoen
nix (2009), (Ref. Appendix F)..
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TABLE 5: SUMMARY OF EXISTING NOISE MEASUREMENTS
Site

Location

Type of
Land
Use

Dur.1

Start
Time,
hh:mm

LT1
LT2
LT3

1600 W Main St
617 W Main St
456 E Main St

24-hour
24-hour
24-hour

LT4

Mesa Arts
Center
1504 W Main St
1310 W Main St
951 W Main St
944 W Main St
630 W Main St
250 W Main St
2301 W Main St

SFR4
SFR
Pioneer
Park
Theater
Motel
Motel
Motel
MFR5
Motel
Motel
Vacant
Parcel
Vacant
Parcel

M1
M2
M3
M4
M5
M6
M76
M86

NEC Apache
Blvd & Smith Rd
(Tempe)

Leq(Day),
dBA3

Leq(Night),
dBA3

Ldn,
dBA3

----

Dist. from
Center of
Main St.,
ft2
80
80
65

69.1
62.9
67.6

63.8
57.7
62.5

71.5
65.3
70.1

24-hour

--

145

58.7

52.7

60.6

15-min.
15-min.
15-min.
15-min.
15-min.
15-min.
1-hour

09:31 AM
09:57 AM
10:21 AM
10:46 AM
11:12 AM
11:42 AM
09:17 AM

50
55
95
67
50
135
55

66.5
66.0
64.4
63.6
69.0
61.1
66.3

--------

--------

1-hour

10:34 AM

50

64.0

--

--

Source: HDR Inc., Phoenix (2009).
1
Duration of measurement. 24-hour measurements are considered long-term (LT) and the 15-minute measurements
are considered short-term for this project.
2
The distance of the microphone from the centerline of Main Street. The total width of Main Street (including lanes in
both directions) was approximately 80 ft at all sites.
3
Daytime is the hours between 7 AM and 10 PM. Nighttime is the hours between 10 PM and 7 AM. For LT sites
Leq(day) represents the average of noise measured during the 15 daytime hours. Leq(night) represents the average
of noise measured during the 9 nighttime hours. Ldn is the 24-hour noise level which takes the Leq day and night
noise levels and adds a 10 dB penalty to noise events occurring during the 9 nighttime hours to recognize the
increased disturbance caused by high noise levels occurring during nighttime sleeping hours.
4
SFR = Single-Family Residence
5
MFR = Multi-Family Residence
6
Sites M7 and M8 are located along the LRT Starter Line and are not in the Central Mesa LRT Extension corridor.

2.2

EXISTING CONDITIONS – VIBRATION

Existing vibration sources in the proposed project alignment primarily consist of
vehicular traffic and intermittent construction activities. Vehicular traffic was the only
permanent vibration source observed along the project corridor. When vehicular traffic
does cause perceptible vibration, the source can usually be traced to potholes, wide
expansion joints, or other “bumps” in the roadway surface. Therefore, the FTA
assessment procedures for vibration from rail transit projects do not require
measurements of existing vibration levels.
Localized geologic conditions such as such soil stiffness, soil layering, and depth to bed
rock, have a strong effect on groundborne vibration. Unfortunately, it is difficult to obtain
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information on subsurface conditions in sufficient detail that computer models can be
used to accurately predict ground vibration. As a result, most detailed predictions of
ground vibration are largely based on empirical methods that involve measuring
vibration propagation in the soil. FTA defines three levels of vibration assessment (Ref.
1):
1. Screening: Generalized distances of potential impacts are used to quickly
determine whether there is any potential for an impact.
2. General Assessment: FTA provides a general curve of vibration level vs.
distance that is used to estimate the vibration levels. The curve was developed
by plotting measured vibration levels from a number of different rail transit
systems against distance from the tracks and drawing a line through the top
range of the data. The curve is intended to give a conservative (high) estimate of
potential vibration impacts. Adjustments are made to the general curve to
account for factors such as speed and special trackwork.
3. Detailed Assessment: A Detailed Vibration assessment consists of using stateof-the-art tools to characterize how localized soil conditions will affect the levels
of groundborne vibration. The FTA guidance manual recommends using a
vibration propagation test to measure how vibration will be transmitted from the
light rail tracks through the ground and into the foundations of nearby buildings
(Ref. 1). The procedure is illustrated in Figure 7. It basically consists of using a
dropped weight as a vibration source and determining the transfer function
relationship between the force generated by the dropped weight and the resulting
vibration pulse. As shown in Figure 7, the impacts are done in a line located as
close to the planned track centerline as possible and accelerometers are located
at several distances from the impact line. In addition, accelerometers can be
located inside nearby buildings to provide information on the complete
propagation path from the track centerline to occupied spaces of the building.
2.2.1 Vibration Propagation Test Procedure
The vibration predictions for Mesa LRT Extension are based on the Detailed
Assessment approach recommended in the FTA manual (Ref. 1). Vibration propagation
tests were performed at four locations using a line of 11 impact positions (referred to in
Figure 7 as the “line of impacts”). The relationship between the exciting force and the
resulting vibration levels is referred to as the “transfer mobility”, which indicates how
easily vibration travels through the earth.
The measured transfer mobility functions for each accelerometer are combined using
numerical integration to derive an equivalent line-source transfer mobility (LSTM). The
relationship between the LSTM and the groundborne vibration created by a LRV is
assumed to be:
Lv = FDL + LSTM

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where:
w
Lv
F
FDL
LSTM

= Train vibrration veloccity measured at the grround surfa
ace
= Force den
nsity functio
on that characterizes the
t vibration forces
generated
d by the tra
ain and tracck
= Measured
d line sourcce transfer mobility
m
(all quanttities are in decibels asssuming a consistent
c
s of
set
decibel re
eference va
alues)

The FDL
L used for this projectt was deve
eloped from
m measurem
ments on th
he existing LRT
Starter Line. The results of the METR
RO LRT measuremen
m
nts and the derived FDL
functions for embe
edded trackk are summ
marized in Appendix C.
C The prrediction cu
urves
developed from th
he propaga
ation testin
ng are pre
esented in Section 4.3
4 and de
etails
presente
ed in Appe
endix B. Additional
A
in
nformation about the fundamenttals of vibra
ation
may be found in Ap
ppendix A.
FIGURE
E 7: SCHEM
MATIC OF VIBRATIO
ON PROPAGATION TEST

2.2.2 Vibration
V
Prropagation Test Sites
The four sites for the vibratio
on propaga
ation tests were selected to rep
present the
e soil
condition
ns of the vibration
v
se
ensitive recceptors alon
ng the Cen
ntral Mesa LRT Exten
nsion
project corridor.
c
Details on th
he measurrement site
es and the measurem
ment resultss are
presente
ed in Appe
endix B. Th
he general locations of the four test sitess are show
wn in
Figure 8 and descrribed below
w:
Site V1 – East Va
alley Institute of Tec
chnology (EVIT) (Figu
ure 9): Thiss measurem
ment
site wass located att the southw
west corner of Main Street
S
and Longmore.
L
Measurem
ments
were takken in the west-most parking lo
ot of EVIT. The Health
h Sciencess building iss set
back 40
00 ft from th
he propose
ed alignmen
nt and is th
he closest building
b
on the campu
us to
Main Street. The impact liine was along
a
the shoulder of Main Street
S
and the
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accelerometers were placed at distances of 25, 50, 75, 100, 150, and 200 ft from the
impact line towards the Health Sciences building.
Site V2 – Epernay Apartment Homes (Figure 10): This site was located east of Alma
School Road. The vibration measurements were performed in the parking lot of the
Epernay Apartments at 944 West Main Street. The impact line was along the north
shoulder of Main Street at the western edge of the apartment property. Accelerometers
were placed at 25, 50, 75, 100, 150, and 200 ft from the impact line.
Site V3 – Downtown Mesa (Figure 11): This measurement site was located in
Downtown Mesa on the north side of Main Street in an alley between Robson and
McDonald. The impact line was along the north shoulder of Main Street and the
accelerometers were placed in an alley between buildings immediately to the north of
Main Street. The alley is mid way between Robson and Macdonald, and open only to
pedestrians. Accelerometers were placed at 25, 50, 75, 100, 150, and 175 ft from the
impact line.
Site V4 – Mesa Arts Center (Figure 12): This measurement was performed in the
courtyard area in front of the Arts Center. The Ikeda Theater is the closest performance
space at the Arts Center to the proposed alignment of the Central Mesa LRT Extension.
The Ikeda Theater is set back from Main Street by approximately 150 ft. The impact line
was along the south shoulder of Main Street, in front of the Arts Center. The
transducers were placed at 25, 50, 100, and 138 ft from the impact line. The transducer
at 138 ft was located at the setback distance of the Arts Center building structure from
Main Street. Two transducers were placed inside the Arts Center, one in the lobby of
the box office area and another on the floor of the Ikeda Theater auditorium.

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FIGURE 8: LOCATIONS OF VIBRATION PROPAGATION TEST SITES

Source: ATS Consulting, 2009
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FIGURE 9:
9 SITE V1, EAST VA
ALLEY INST
TITUTE OT
T TECHNOLOGY

FIGU
URE 10: SIT
TE V2, EPE
ERNAY AP
PARTMENT
T COMPLEX

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FIGURE 11: SITE V3, DOWNTOWN MESA

FIGURE 12: SITE V4, MESA ARTS CENTER

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2.2.3 Results of Vibration Propagation Tests
The measured LSTM and coherence for sites V1 through V4 are shown in Figure 13
through Figure 16. Additional details of the test results are given in Appendix B. The
use of these results to develop vibration prediction curves is discussed in Section 4.3. A
few key observations from inspection of the propagation test results are:
x

The transfer mobility spectra and vibration attenuation with distance are very
similar for sites V2 through V4 at distances beyond 25 ft from the impact line.

x

The measured transfer mobility at V1 (Figure 13) is consistently lower than at the
other three sites except at 25 ft. There is a strong peak between 40 and 80 Hz at
the 25 ft position. Because none of the other test results have a similar peak, it is
likely that this peak was caused by an unusual condition at the 25 ft position such
as underground utility tunnel of some sort. The peak is unlikely to represent the
general ground characteristics in the project corridor.

x

The LSTM spectra are relatively flat between 20 and 100 Hz. The coherence
over this frequency range exceeds 0.5 except at the more distant measurement
positions. Coherence is a measure of the “quality” of the transfer mobility data. A
coherence close to one indicates a very strong relationship between the exciting
force and the resulting ground vibration, and a coherence close to zero indicates
a weak relationship between the two. A low coherence is usually an indication
that the background vibration at the accelerometer position exceeds the vibration
generated by the dropped weight. A coherence greater than 0.5 indicates a
reasonably good correlation between the vibration source and the receiver.

x

As discussed in Section 4.3, because the LSTM at Site V1 was substantially
lower than at the other three sites except for the anomalous result at 25 ft, the
Site V1 data was not used for the vibration impact predictions. This is a
conservative approach that avoids underestimating vibration impacts.

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FIGURE 13: MEASURED LSTM AND COHERENCE, SITE V1

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FIGURE 14: MEASURED LSTM AND COHERENCE, SITE V2

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FIGURE 15: MEASURED LSTM AND COHERENCE, SITE V3

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FIGURE 16: MEASURED LSTM AND COHERENCE, SITE V4

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3.

REGULATORY FRAMEWORK

3.1

STATE AND LOCAL NOISE AND VIBRATION LIMITS

There are no state statutes related to noise criteria that apply to the operation of the
proposed project. The FTA Noise and Vibration guidelines have been used for this
evaluation. The FTA guidelines, analysis methods and criteria reflect the best available
research on the topic. The City of Mesa has ordinances that place limits on construction
noise and would apply to construction of the proposed project.
3.2

FTA NOISE IMPACT CRITERIA

The noise impact criteria to be used on federally financed transit projects are defined in
the FTA Guidance Manual (Ref. 1). The FTA criteria are based on the best available
research on community response to noise. This research shows that characterizing the
overall noise environment using measures of noise “exposure” provides the best
correlation with human annoyance.
Table 6 lists the three land-use categories that FTA uses and the applicable noise
metric for each category. For Category 2 land uses, noise exposure is measured using
Ldn while for Category 1 and Category 3 land uses, noise exposure is measured using
Leq. It is noteworthy that Category 2 land uses (residential) include residences, motels,
hotels and any other place where people normally sleep. Appendix A includes a
background for these noise descriptors. The basic concept of the FTA noise impact
criteria is that more project noise is allowed in areas where existing noise is higher, but
that the decibel increase in total noise exposure (the decibel sum of existing noise and
project noise) decreases.
FTA defines two levels of noise impact: moderate and severe. In accordance with the
FTA Guidance Manual, noise mitigation to eliminate noise impacts must be investigated
for both degrees of impact. The Manual also states that for severe impacts “…there is a
presumption by FTA that mitigation will be incorporated in the project unless there are
truly extenuating circumstances which prevent it.” In considering mitigation for severe
impacts in this study, the goal has been to reduce noise levels to below the moderate
impact threshold.
FTA allows more discretion for mitigation of moderate impacts, based on consideration
of factors that include cost, number of sensitive receptors affected, community views,
the amount that the predicted levels exceed the impact threshold, and the sensitivity of
the affected receptors. The FTA noise impact criteria are given in tabular format in
Table 7 with the thresholds rounded off to the nearest decibel. The criteria are shown
graphically in Figure 17 for the three different categories of land use along with an
example of how the criteria are applied. The top two graphs are for nonresidential land
uses where Leq(h) is used as the noise exposure metric, and the bottom left graph is for
residential land uses where Ldn is used as the noise exposure metric. As seen in
Figure 17, the impact threshold is a sliding scale and the impact threshold typically
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increases with an increase in existing noise exposure. The existing noise is shown on
the horizontal axis, and the amount of new noise that can be created by the project is on
the vertical axis. The lower curve (blue) defines the threshold for Moderate Impact and
the upper curve (red) defines the threshold for Severe Impact.
TABLE 6: FTA LAND USE CATEGORIES AND NOISE METRICS
Land Use
Category
1

Noise Metric
(dBA)
Outdoor Leq(h) (1)

2

Outdoor Ldn

3

Outdoor Leq(h) (1)

Description of Land Use Category
Tracts of land where quiet is an essential element of their intended
purpose. This category includes lands set aside for serenity and
quiet and such land uses as outdoor amphitheaters and concert
pavilions, as well as National Historic Landmarks with significant
outdoor use. Also included are recording studios and concert halls.
Residences and buildings where people normally sleep. This
category includes homes, hospitals and hotels where a nighttime
sensitivity to noise is assumed to be of utmost importance.
Institutional land uses with primarily daytime and evening use. This
category includes schools, libraries, 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 can also be
considered to be in this category. Certain historical sites and parks
are also included.

Source: FTA 2006.
Notes:
(1) Leq for the noisiest hour of transit related activity during hours of noise sensitivity.

The concept of a sliding scale for noise impact is difficult to grasp and may be clarified
by the example illustrated in the bottom right graph in Figure 17. Assume that the
existing noise has been measured to be 60 dBA Ldn. This is the total noise from all
existing noise sources over a 24-hour period: traffic, aircraft, lawn mowers, children
playing, birds chirping, etc. Starting at 60 dBA on the horizontal axis, follow the vertical
line up to where it intersects the moderate and severe impact curves. Then refer to the
left axis to read off the impact thresholds. As shown in the example, an existing noise of
60 dBA Ldn gives thresholds of 57.8 dBA Ldn for moderate impact and 63.4 dBA Ldn
for severe impact. Note that the values are given in tenths of a decibel to avoid
confusion from rounding off; in reality it is not possible to perceive a tenth of a decibel
change in sound level.
The thresholds of 57.8 dBA and 63.4 dBA are for the project noise, which is defined as
the new noise that is generated by operation of the transit project. If the predicted
project noise is greater than 57.8 dBA Ldn, then there is moderate impact and noise
mitigation must be considered. If the predicted project noise exceeds 63.4 dBA Ldn,
then there is severe impact and, as discussed above, noise mitigation must be included
in the project unless there are compelling reasons why mitigation is unfeasible.

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FIGURE 17: FTA NOISE IMPACT CRITERIA

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TABLE 7: FTA NOISE IMPACT CRITERIA
Existing Noise Exposure
Leq or Ldn
<43
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
>77

Project Noise Exposure Impact Thresholds, Ldn or Leq (dBA)
Category 1 or 2 Sites
Category 3 Sites
Moderate Impact Severe Impact Moderate Impact Severe Impact
Ambient+10
Ambient+15
Ambient+15
Ambient+20
52
58
57
63
52
58
57
63
52
58
57
63
53
59
58
64
53
59
58
64
53
59
58
64
54
59
59
64
54
59
59
64
54
60
59
65
55
60
60
65
54
60
60
65
55
61
60
66
56
61
61
66
56
62
61
67
57
62
62
67
57
62
62
67
58
63
63
68
58
63
63
68
59
64
64
69
59
64
64
69
60
65
65
70
61
65
66
70
61
66
66
71
62
67
67
72
63
67
68
72
63
68
68
73
64
69
69
74
65
69
70
74
65
70
71
75
66
71
71
76
66
71
71
76
66
72
71
77
66
73
71
78
66
74
71
79
66
74
71
79
66
75
71
80

Source: FTA, May 2006 (Ref. 1)
Note: Ldn is used for land uses where nighttime sensitivity is a factor; maximum 1-hour Leq is used for land use
involving only daytime activities.

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3.3

CITY OF MESA LIMITS ON CONSTRUCTION NOISE

The noise ordinance of the City of Mesa restricts the hours of operation for construction,
demolition or excavation equipment within a residential zone or any property within a
radius of 500 ft of a residential zone. The limits on construction noise in the ordinance
are:

3.4

x

Allowed construction hours during weekdays of the months of May, June, July,
August, and September: 5 AM to 6 PM.

x

Allowed construction hours during weekdays of the remaining months of the
year: 6 AM to 6 PM.

x

Operation of construction equipment operation is prohibited on Sundays and
legal holidays of all 12 months of the year.

x

Restricted permits for regular or emergency construction during prohibited hours
may be obtained from the Building Safety Director of the City of Mesa. The
Building Safety Director will determine if public health and safety will be impaired
from construction during the prohibited hours before issuing a permit.
FTA VIBRATION IMPACT CRITERIA

As discussed in Appendix A, the potential adverse effects of rail transit groundborne
vibration include perceptible building vibration, rattle noises, reradiated noise
(groundborne noise), and cosmetic or structural damage to buildings. The vibration
caused by light rail operations is well below what is considered necessary to damage
buildings. Therefore, the criteria for building vibration caused by transit operations are
only concerned with potential annoyance of building occupants. One potential concern
is historic buildings and other cultural resources that may be fragile and particularly
susceptible to damage from ground motions. Several historic buildings and other
resources have been identified along the alignment. However, none of the structures
appear to be unusually fragile. Therefore, the vibration assessment of these structures
is based on the current use of the building. The potential for construction vibration to
damage structures during construction is covered in Section 5.4 (Construction
vibration).
The FTA vibration impact criteria are based on the maximum indoor vibration level as a
train passes. There are no impact criteria for outdoor spaces such as parks. The FTA
Guidance Manual (Ref. 1) provides two sets of criteria: one based on the overall
vibration velocity level for use in General Vibration Impact Assessments and one based
on the maximum vibration level in any 1/3 octave band (the band maximum level) for
use with a Detailed Vibration Assessment, which was used for this project.
Table 8 shows the FTA General Assessment criteria for groundborne vibration from rail
transit systems. As with the FTA noise criteria, there are three categories of sensitive
land uses. However, the category definitions are different for noise and for vibration.
The primary difference is in Category 1. For a noise assessment, Category 1 applies to
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land uses “…where quiet is an essential element of their intended purpose.” For a
vibration assessment, Category 1 applies to “Buildings where vibration would interfere
with interior operations,” which primarily applies to spaces that house sensitive research
and laboratory equipment such as scanning electron microscopes. The Health Sciences
building in the East Valley Institute of Technology (EVIT) campus is the only building in
the project corridor that potentially qualifies for FTA Category 1 land use.
TABLE 8: FTA IMPACT THRESHOLDS FOR GROUNDBORNE VIBRATION
GENERAL IMPACT ASSESSMENT
Land Use Category

Ground Borne Vibration
(VdB re 1 micro inch/sec)
Frequent
Occasional
Infrequent
Events
Events
Events

Category 1. Buildings where vibration would
interfere with interior operations. Typically
land uses include vibration-sensitive research
and manufacturing, hospitals with vibrationsensitive equipment, and university research
operations.
Category 2. Residences and buildings where
people normally sleep.
Category 3. Institutional land uses with
primarily daytime use.

65 VdB

65 VdB

65 VdB

72 VdB

75 VdB

80 VdB

75 VdB

78 VdB

83 VdB

Source: Federal Transit Administration 2006.
Notes:
a. Frequent events defined as more than 70 vibration events per day.
b. Occasional events is defined as between 30 and 70 events per day.
c. Infrequent events is defined as less than 30 events per day.
d. Vibration sensitive equipment is not sensitive to groundborne noise.

Unlike the FTA noise criteria, the vibration criteria do not incorporate any factor to
account for the number of trains per day with one exception. The exception is that for
“occasional service,” the FTA impact thresholds are 3 VdB higher than for “frequent
service” and for “infrequent service,” the FTA impact thresholds are 8 VdB higher than
for frequent service. FTA defines occasional service to be between 30 and 70 trains per
day and infrequent service to be less than 30 trains per day. The frequent criteria are
applicable to the Central Mesa LRT Extension project as there would be more than 70
trains per day.
The FTA vibration thresholds do not specifically account for existing vibration. Although
Main Street has substantial volumes of vehicular traffic including buses and trucks, it is
relatively rare that rubber-tired vehicles will generate perceptible ground vibration unless
there are irregularities in the roadway surface such as potholes or wide expansion
joints. As such, it is expected that current conditions along the proposed project corridor
do not include more than isolated cases where traffic generated groundborne vibration
is perceptible.
The refined criteria for use with Detailed Vibration Assessments are shown in Figure 18.
For the Detailed Assessment, the predicted vibration levels in terms of the 1/3 octave
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band spectra are compared to the curves shown in Figure 18 to determine whether
there is impact and the frequency range over which vibration mitigation is required.
Impact occurs when any spectral values exceed the applicable curve. The FTA
interpretation of how each of the curves shown in Figure 18 should be applied is given
in Table 9. The VC-A through VC-E curves are used to specify acceptable vibration
limits for sensitive equipment such as electron microscopes. The VC-A through VC-E
curves are used to evaluate potential impacts to spaces used for vibration-sensitive
equipment. Which curve to use depends on the sensitivity of the specific equipment that
would be affected. With the exception of a few particularly sensitive pieces of equipment
such as Transmission Electron Microscopes (TEM) or Atomic Force Microscopes
(AFM), the VC-C curve is adequate to meet avoid interfering with the operation of most
sensitive equipment.
The use of the Detailed Vibration Assessment criteria is illustrated by the example
vibration spectrum (the blue dashed line) shown in the lower right graph in Figure 18.
The maximum level of the spectrum exceeds the “Residential (Night)” curve in the 50
and 63 Hz 1/3 octave bands and all of the 1/3 octave band levels are below the
“Residential (Day)” curve. For this example, impact would be predicted for residential
land uses and vibration mitigation would need to be evaluated. Typical sensitive
equipment and their appropriate VC-curves are listed in Table 9.
The approach used for this project is that the General Assessment criteria of Table 8
were used to identify potential vibration impacts. Then the Detailed Assessment criteria
were applied to determine whether vibration mitigation would be warranted.
There are some buildings, such as concert halls, recording studios and theaters, which
can be very sensitive to vibration but do not fit into any of the three categories listed in
Table 8 or associated with the curves in Figure 18. Due to the sensitivity of these
buildings, they usually warrant special attention during the environmental evaluation of a
transit project. Table 10 gives the FTA criteria for acceptable levels of groundborne
vibration and groundborne noise for various categories of special buildings.
The only building along the project corridor where special building criteria have been
applied is the Mesa Arts Center. The criteria for concert halls listed in Table 10 have
been used to evaluate potential vibration impacts to the auditorium spaces of the Mesa
Arts Center.

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FIGURE 18: FTA CRITERIA FOR DETAILED VIBRATION ANALYSIS

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TABLE 9: INTERPRETATION OF VIBRATION CRITERIA FOR DETAILED
ANALYSIS
Criterion Curve Max Lv1
Description of Uses
(VdB)
Workshop
90
Distinctly feelable vibration. Appropriate to workshops and nonsensitive areas.
Office
84
Feelable vibration. Appropriate to offices and non-sensitive
areas.
Residential Day
78
Barely feelable vibration. Adequate for computer equipment and
low-power optical microscopes (up to 20X).
Residential Night,
72
Vibration not feelable, but groundborne noise may be audible
Operating Rooms
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), 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
capability.
VC-E
42
The most demanding criterion for extremely vibration-sensitive
equipment.
Source, FTA 2006 (Ref. 1)
Notes:
1
Maximum allowed vibration velocity in any 1/3 octave band over the range of 8 to 80 Hz.

TABLE 10: GROUNDBORNE NOISE AND VIBRATION IMPACT CRITERIA FOR
SPECIAL BUILDINGS
Location

Groundborne Vibration Impact Levels Groundborne Noise Impact
(VdB re 1 micro-inch/sec)
Levels
(dB re 20 micro Pascals)
GBV, VdB
GBN, dBA
GBV, VdB
GBN, dBA
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
Source: FTA 2006 (Ref. 1).
GBV = Groundborne vibration, GBN = Groundborne noise.

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4.

NOISE AND VIBRATION METHODOLOGY

4.1

NOISE AND VIBRATION ASSESSMENT APPROACH

The analysis of potential noise and vibration impacts associated with the proposed
project follow the FTA guidelines outlined in the FTA Guidance Manual for a Detailed
Noise Assessment and a Detailed Vibration Assessment. The basic steps in the
assessment are:
1. Identify sensitive receptors. Noise- and vibration-sensitive land uses along the
corridor were identified first using aerial photography. Field visits were then
conducted to confirm land uses and gather additional relevant information, such
as the presence of second stories, sound walls, or intervening structures.
Sensitive receivers were then grouped together in clusters based on their
location relative to the tracks and operational factors such as train speed that
affect noise and vibration levels. The predictions for each cluster were based on
the distance from the proposed project to the closest sensitive receptor. The
clusters used for the assessment are shown in Appendix E.
2. Determine existing conditions. As discussed in Section 2.0 and Appendix F,
measurements of existing noise levels were taken along the project corridor at
three sites for 24-hours and eight sites for 15-minutes each. The measurements
were used to estimate the existing Ldn and daytime Leq at all of the sensitive
receptor clusters. Because the only significant source of existing vibration in the
corridor is vehicular traffic and because traffic rarely causes perceptible vibration,
FTA procedures do not require measuring existing vibration levels. However,
local geologic conditions will have a strong effect on the vibration levels. The
manner in which ground vibration will be transmitted from the tracks to nearby
buildings was documented through four vibration propagation tests. The results
of the vibration testing are summarized in Section 2 and in Appendix B.
3. Develop prediction models. The noise predictions models are based on formulas
provided in the FTA Guidance Manual (Ref. 1), equipment specifications, and
noise measurements of the existing LRT Starter Line. The predictions of train
noise are based on the forecast future number of daily trains and the distribution
of these trains throughout the day (early morning, daytime, and nighttime), the
distance from the tracks, the train speed, the presence of walls, berms, or other
structures that could reduce noise levels, and other site specific conditions.
Similarly, models were developed to predict noise from TPSS units and the train
bells. The vibration prediction models were based on measurements of train
vibration on the starter line and the vibration propagation test results.
4. Estimate future noise and vibration levels at the representative receivers. The
predictions were compared to the applicable FTA impact thresholds to identify
potential noise and vibration impacts. See Section 5.0 for a discussion of the
predicted noise and vibration levels.
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5. Evaluate mitigation options. Mitigation options were evaluated for all locations
where the predicted noise or vibration levels exceed the FTA impact thresholds.
4.2

NOISE PREDICTION MODELS

Different models are used to predict noise from operations and TPSS units.
4.2.1 Prediction Model, Noise from Light Rail Vehicle Operations
Measurement of the noise generated by METRO vehicles operating on the LRT Starter
Line is the basis for predictions of the LRV noise for the Central Mesa LRT Extension
project. Details of the noise measurements are presented in Appendix D. The reference
levels used for this analysis are:
x

Maximum sound level (Lmax), two car train operating at 35 mph on embedded
track at a distance of 50 ft: 77 dBA

x

Train speed: 25 mph

x

Train length: 2 cars for all trains. Three-car trainswould be used occasionally for
special events or other periods of high demand. Most 3-car trains would be
operated during daytime and evening hours (7 AM to 10 PM), which would have
a minimal effect on the noise predictions. Therefore, a 2-car consist has been
used as the normal train configuration for all noise modeling.

These values were used with formulas included in the FTA Guidance Manual (Ref. 1) to
predict the noise levels at each cluster of sensitive receptors. The principal formulas
are:
Relationship between Lmax and SEL:

SEL
where:
speed =
length =
y=
=

ª speed
º
2D  sin 2D »  3.3
Lmax  10 u log «
¬ length
¼

Velocity in mph
Length of train in feet (e.g. 2 car LRT = 190 ft)
Distance from receiver to track centerline
tan-1(length/2y)

Change in sound level with speed:

·
'SEL 20 log§¨ speed2
¸
speed
1¹
©
where:
speed1 =
speed2 =
SEL =

Initial speed
New speed
Change in SEL for speed change from speed1 to speed2

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Calculation
C
n of Ldn an
nd hourly Leq
L from SEL:
L DNN SEL  10
0 u log NTra
ain DAY  10 u NTrain
L EQ ( Hou
ur )

NIIGHT

 49 .4

SEL  10 u log NT
Train HOUR  35.6

where:
w
N
NTrain
o trains during daytim
me hours
DAY = Number of
N
NTrain
o trains during nighttim
me hours
NIGHT = Number of
N
NTrain
o trains during one ho
our
HOUR = Number of
The asssumed ope
erating schedule is 10
0 minute service
s
durring daytim
me and eve
ening
hours (5
5 AM to 8 PM)
P
and 20
0 minute se
ervice durin
ng late nigh
ht hours (affter 8 PM). This
schedule
e gives a total
t
of 102
2 trains in each direcction per da
ay, 84 during the dayytime
hours (7
7 AM to 10 PM) and 18
8 during the
e nighttime hours (10 PM
P to 7 AM
M).
Figure 19 shows the
t
predictted LRV sound
s
leve
el vs. dista
ance from the near track
t
centerlin
ne in terms of Ldn and
d the maxim
mum sound level durin
ng the passing of a two
o-car
train at 35
3 mph. A separation distance of
o 14 ft betw
ween the ne
ear and far track was used
to generrate the currve in Figurre 19.
There are a few locations alo
ong the projject corrido
or where exxisting strucctures woulld be
d or altered
d due to wid
dening of the roadwayy for the prroposed pro
oject. Howe
ever,
acquired
removing or altering these strructures wo
ould not sub
bstantially alter
a
the acoustic shielding
of any sensitive rec
ceiver in the
e corridor.
FIGU
URE 19: LR
RT SOUND LEVELS VS
V DISTANCE FROM TRACK CENTERLIN
NE
(2
2-car trains operating on
o embedd
ded track att 35 mph)

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esa LRT Extens
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4.2.2 Prediction model, Noise from Audible Warnings
The bells are installed on the light rail vehicles trains at the both ends of the vehicles
and are activated at the front and rear of the lead vehicle and the rear of the trailing
vehicle. The noise from bells is modeled based on sound level that the bells are set to
on the LRT Starter Line and the assumption that the bells are point sound sources. The
bell reference sound level is assumed to be a maximum sound level (Lmax) of 80 dBA
at a distance of 50 ft from the bell. Although the bells are mounted on the trains, the
bells are modeled as a point sound source because it is expected that in normal use
they will be sounded in two short intervals only 1) when entering and exiting stations
and 2) at stoplights when the train starts after stopping for the signals. A reasonable
assumption is that approximately half of the trains would sound the bell at signaled
intersections since the bells would only be sounded when the signal requires the train to
stop at an intersection. The bell noise model also assumes that the bells will be
sounded by all trains when entering and exiting stations.
The principal formulas used for this analysis are:
Relationship between Lmax and SEL:
SEL Lmax  10 u log>T @
where:
T=
duration of the maximum bell noise
Calculation of Ldn and hourly Leq from SEL:
L DN SEL  10 u log NTrain DAY  10 u NTrain NIGHT  49 .4
L EQ ( Hour )

SEL  10 u log NTrain HOUR  35.6

where:
NTrainDAY = Number of trains during daytime hours
NTrainNIGHT = Number of trains during nighttime hours
NTrainHOUR = Number of trains during one hour
Calculation of bell noise at individual receiver:

Lp

·¸
Lpref  20 u log§¨ D
Dref
©
¹

where:
D = Distance to receiver from the centerline of the tracks
Dref = Reference distance from the bells (50 ft)
Lp = Level of bell noise at receiver
Lpref = Bell noise level at reference distance (50 dBA)

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4.2.3 Prediction Model, Ancillary Equipment
The only ancillary equipment expected to have the potential of causing noise impacts
are the Transit power substations (TPSS) units. The primary noise sources on TPSS
units are the transformer hum and noise from cooling systems. On most modern TPSS
units the transformer hum is minimal so only the ventilation and cooling system has
potential to cause noise impacts.
A recent noise measurement of a TPSS unit used in a residential area along the Los
Angeles Metro Gold Line showed that the ventilation fan generated a sound level of 51
dBA at a distance of 40 ft from the fan. This is equivalent to an Leq of 49 dBA at a
distance of 50 ft (the measurement was not done at 50 ft because of obstructions),
which is equivalent to an Ldn of 54 dBA at 50 ft. The measured noise level is consistent
with the limit of 50 dBA at 50 ft from any side of the TPSS that has been included in the
purchase specifications for TPSS units on several recently completed light rail systems.
It has been assumed that similar units will be used on the Central Mesa LRT extension.
The following formula has been use to estimate TPSS noise for this project:

Lp

·¸
Lpref  20 u log§¨ D
Dref
©
¹

where:
D = Distance to receiver from the TPSS unit cooling fan
Dref = Reference distance from the TPSS unit cooling fan (50 ft)
Lp = Level of TPSS noise at receiver
Lpref = TPSS sound level at reference distance (50 dBA)
4.3

VIBRATION PREDICTION MODEL

The predictions of groundborne vibration for this study follow the Detailed Vibration
Assessment procedure of the FTA Guidance Manual (Ref. 1). This is an entirely
empirical method based on testing of the vibration propagation characteristics of the soil
in the project corridor and measurements of the vibration characteristics of a similar light
rail vehicle. As discussed in Section 2.0, vibration propagation tests were performed at
four locations in the proposed corridor for the Central Mesa LRT Extension Project. The
quantity derived from the propagation tests is referred to as the Line Source Transfer
Mobility (LSTM). The results of propagation tests are presented in Section 2.2 and
Appendix B.
The basic relationship used for the vibration predictions is:
Lv = FDL + LSTM
where:
Lv =
Train vibration velocity measured at the ground surface
LSTM =
Measured line source transfer mobility
FDL =
Force density function that characterizes the vibration forces
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generated by the train and track
(All quantities are expressed in decibels using a consistent set of decibel
reference values)
FDL is derived by measuring Lv and LSTM at a site where there are train operations.
For this project, the FDL of the METRO Starter Line was measured in the driving alley
of 5552 East Washington Street, Phoenix. The results of the FDL measurements at this
site are shown in Figure 20 for train speeds of 15 and 25 mph. Details of the FDL test
and results at more speeds are given in Appendix C. Figure 20 shows that the FDL
peaks at 80 Hz for the 25 mph curve and there is no significant low frequency FDL
component. It is noteworthy that at speeds higher than 25 mph, there is a potential for
higher low frequency FDL components as shown in Appendix C.
As discussed in Section 2.2, three of the four propagation tests in the project corridor
resulted in very similar LSTM curves. The LSTM curves from the other site (Site V1)
were lower except for an anomalous result at the 25 ft position. The approach used for
the vibration predictions was to combine the results from sites V2, V3 and V4 to
calculate average LSTM curves. The LSTM curves used for the predictions are shown
in Appendix B.
Figure 21 through
Figure 23 shows the 1/3 octave band spectra of the predicted vibration at distances of
25, 50 and 100 ft from the track centerline for train speeds of 33, 29 and 22 mph. Also
shown in Figure 21 are the Detailed Assessment impact curves for residential land
uses. The attenuation of the overall vibration level with distance is shown in Figure 24.
Figure 21 through Figure 24 do not include the adjustments for speed, special trackwork
and potential amplification by floor resonances that were used in the actual predictions.
However, the figures do provide an indication for the degree of vibration impact to
expect. Specifically, Figure 21 through Figure 24 show that:
x

The predicted overall vibration level is below the FTA General Assessment
impact threshold for Category 2 (residential) land uses at distances greater than
55 ft from the near track centerline (see Figure 24).

x

The predicted overall vibration level is below the FTA General Assessment
impact threshold at distances for Category 3 (institutional) land uses greater than
40 ft from the near track centerline (see Figure 24).

x

The predicted vibration levels are below the Detailed Assessment impact
threshold for Category 2 (residential land uses) at distances greater than 25 ft
from the near track centerline (Figure 21). Note that the FTA criteria for
groundborne vibration consider all spaces where people normally sleep as
equivalent. That is, hotels, motels, apartment buildings, and single family
residences are all considered Category 2 land uses and have the same impact
thresholds for groundborne vibration.

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FIGURE 20: METRO LRT FORCE DENSITY AT 15 AND 25 MPH

FIGURE 21: PREDICTED LRV VIBRATION SPECTRUM AT 33 MPH
(Curves do not include adjustments for floor amplification or a safety factor)

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FIGURE 22: PREDICTED LRV VIBRATION SPECTRUM AT 29 MPH
(Curves do not include adjustments for floor amplification or a safety factor)

FIGURE 23: PREDICTED LRV VIBRATION SPECTRUM AT 22 MPH
(Curves do not include adjustments for floor amplification or a safety factor)

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FIGURE 24: PREDICTED OVERALL VIBRATION VERSUS DISTANCE
(The horizontal lines are the FTA General Assessment impact thresholds
for Category 2 and Category 3 land uses. The curves do not include
adjustments for floor amplification or a safety factor)

The curves in Figure 21 through Figure 24 were used for the base vibration predictions
and then the following adjustments were applied to estimate vibration levels at occupied
spaces of buildings:
x

Speed Adjustment: Because the force density tests were performed at a number
of different speeds, speed was accounted for by using the appropriate FDL.

x

Special Trackwork: The additional vibration at special trackwork was accounted
for by adding 10 VdB to the predicted vibration levels when a crossover frog
would be located less than 100 ft from a sensitive receptor.

x

Coupling Loss, Floor Amplification, Safety Factor: A 3 to 5 decibel safety factor
was added to the predicted vibration levels to account for the combined effects of
coupling loss at the soil/foundation interface and amplification by the building
structure and to provide a small “safety” factor to the predictions. Two things
happen as vibration is transmitted from the ground, into the building foundation,
and through the building into occupied spaces. First, the interaction at the
foundation/soil interface tends to reduce the vibration amplitudes transmitted into
the building foundation. Second, when the vibration reaches occupied spaces of

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the building, various resonances in the building components may amplify the
vibration. Both of these effects can be substantial and are difficult to predict.
Experience is that the average combined effect is close to zero for wood frame
residential structures, although for some buildings with flexible floors the indoor
vibration may be as much as 10 decibels higher than the outdoor vibration. For
larger buildings with more massive foundations, the net effect is more likely to be
a 5 to 10 decibel reduction in the vibration levels.
The safety factors for the sensitive receivers along the Central Mesa LRT
Extension varied depending on the type of vibration analysis and the type of
building structure. For the initial General Assessment (GA) of vibration impacts, a
safety factor of 5 decibel was added to the predicted levels. This ensures that the
preliminary estimate of vibration impacts is conservative (on the high side). For
the Detailed Assessment that refines the preliminary impact estimates, the safety
factors used were:
ƒ

Indoor spaces of motels with single floor: 3 decibels. This is equivalent to
assuming that the indoor vibration is essentially the same as the outdoor
vibration. Because majority of the single floor buildings in the project corridor
use the equivalent of a slab-on-grade construction, this is appropriate for
single floor buildings and first floor units.

ƒ

Second floor units of motels: 5 decibels. Because many of the motel
structures appear to be inexpensive construction, which could mean that the
floors are relatively flexible and prone to amplification, a higher safety factor
of 5 decibel was used.

ƒ

Mobile homes: 5 decibels. Permanent mobile homes anchored to the ground
without any isolation are prone to amplification of ground vibration. Therefore,
the higher safety factor was used.

ƒ

RVs and travel trailers: 3 decibels. The vibration isolation provided by the
pneumatic tires makes these units less prone to amplify vibration. Therefore,
the lower safety factor was used.

This basically represents a “safety factor” to ensure that in the majority of cases
the predicted vibration levels will be higher than what will occur after the
proposed project is operational.

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5.

NOISE AND VIBRATION IMPACT ASSESSMENT

5.1

LRT RELATED NOISE

5.1.1 Operational Noise
The noise sensitive land uses for FTA Categories 1, 2 and 3 along the Central Mesa
LRT Extension project have been grouped into clusters. The clusters group similar land
uses that are about the same distance from the tracks and are small enough that train
speeds and other operational parameters are the same for all land uses in the cluster.
The locations of the clusters and buildings included in each cluster are shown in
Appendix E. The noise predictions are based on the sensitive land use that is closest to
the Central Mesa LRT Extension project.
Table 11 presents the predictions of noise from LRT operations for Category 2 land
uses and Table 12 presents the predictions for Category 3 land uses. Category 2 land
uses include residential, motels, hotels, and mobile home parks and Category 3 land
use include schools, places of worship, child care facilities, and parks that are not
sensitive to noise during nighttime hours. The concert hall auditorium (Ikeda Theater) in
the Mesa Arts Center is the only land use in the corridor identified as Category 1 (highly
sensitive). The predicted noise impact for the Category 1 land use is shown in Table 13.
The columns in the tables provide the following information:
x

Cluster: Cluster number.

x

Desc: Describes the type of land use.

x

Closest Cross Street: Identifies the cross street to Main Street that is closest to
the cluster.

x

Near Track Dist: Distance in feet from the near track to the closest noise
sensitive building in the cluster.

x

Train Speed: Maximum expected train speed on the track closest to the cluster.
The speeds were based on the projected speed profile. The actual train speeds
would often be lower near stations and signal stops.

x

Existing: Existing noise level (Ldn) at each cluster. The measured Ldns
summarized in Table 5 (see Section 2) were used as the base level. These levels
were adjusted based on the distance of the cluster from Main Street and the
distance of the measurement from Main Street. This procedure is appropriate
because the dominant noise source at all of the long-term measurement sites
was traffic on Main Street. The adjustment factor was estimated as
10×log(Dist(measurement)/Dist(cluster)).

x

Project: Predicted future Ldn from train noise. Its noteworthy that because bells
during normal operations are associated with slow speeds of trains, bell noise will

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be the dominate noise source near stops and stations. Therefore sensitive
receivers near stoplights and stations were evaluated for bell noise impacts.
x

Impact Threshold: The FTA impact thresholds for moderate and severe impact
based on the existing noise levels.

x

Number of Impacts: The number of dwelling units where the predicted levels of
LRT noise exceed the Moderate (Mod) and Severe impact thresholds.

Category 3 land uses adjacent to the project corridor include:
x

Buildings on the EVIT campus near Longmore.

x

Childbirth education classes in Downtown Mesa west of Robson and north of the
tracks.

x

The City Hall in downtown Mesa.

x

The Tri-City Community Service Center located at the southeast corner of
Hibbert and Main Street.

x

Pioneer Park located north of the tracks near the eastern end of the alignment.

x

The Mormon Temple located at the eastern end of the alignment

Note that the Landmark Restaurant located at the southwest corner of Main Street and
Extension is one of the NHRP listed structures in the corridor. However, the current use
of the building as a restaurant is not considered a noise sensitive land use, therefore the
building is not included as a noise sensitive land use in the tables. The results of the
noise analysis indicate that none of the other properties listed as eligible are adversely
impacted either because they are commercial buildings not considered noise-sensitive
land uses or because the two eligible residences and one motel along the alignment
were assessed and found to not be adversely affected by project-related noise.
Following is the summary of the noise impact assessment of the proposed project:
x

No noise impacts are predicted from LRT operations at Category 2 (Residential
or other sensitive receptors with both daytime and nighttime use, e.g., hotels,
motels, dormitories) land uses as shown in Table 11.

x

No noise impacts are predicted from LRT operations at Category 3 (Institutional
with primarily daytime use) land uses as shown in Table 12.

x

No noise impacts are predicted from LRT operations at the Category 1 land use
(the Ikeda Theater) as shown in Table 13.

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TABLE 11: SUMMARY OF NOISE IMPACT ASSESSMENT FOR CATEGORY 2
Cluster Desc.a

1
SFR
2
Motel
3
Motel
4
SFR
5
Motel
6
Motel
7
SFR
8
MHP
9
SFR
10
MFR
11
TLR
12
MHP
13
Motel
13A
TLR
14
Motel
15
SFR
16
Motel
16A
TLR
16B
Motel
17
SFR
18
Motel
19
MFR
20
SFR
21
Hotel
2-Lane Option
22
Hotel
23
Hotel
24
SFR
25
SFR
26
SFR
4-Lane Option
22
Hotel
23
Hotel
24
SFR
25
SFR
26
SFR

Near
Track
Dist. b
(ft)
310
50
50
300
50
50
200
50
140
80
220
50
80
55
80
110
45
45
45
360
60
690
180
145

Closest
LRT Exist
Ldn c, (dBA)
# of Impactsf
d
e
Cross Street Speed Noise Existing Project
Impact
(mph) Site
Threshold
Mod Severe Mod Severe
Longmore
33
LT1
66
55
61
66
--Longmore
33
LT1
73
63
65
72
--Rogers
33
LT1
73
63
65
72
--Rogers
33
LT1
66
55
61
67
--Stewart
33
LT1
73
63
65
71
--Stewart
33
LT1
73
63
65
71
--Alma School
29
LT2
61
56
58
64
--Beverly
29
LT2
67
61.6
62
67
--Beverly
29
LT2
63
57
59
65
--Extension
29
LT2
65
60
62
67
--Beverly
29
LT2
61
56
58
64
--Beverly
29
LT2
67
61.6
62
67
--Beverly
29
LT2
65
60
62
67
--Extension
29
LT2
66
61
62
67
--Extension
29
LT2
65
60
62
67
--Extension
29
LT2
64
58
60
65
--Date
29
LT2
67
62
62.3
67
--Date
29
LT2
67
62
62.3
67
--Date
29
LT2
67
62
62.3
67
--Date
29
LT2
59
53
57
63
--Date
29
LT2
66
61
62
67
--Date
29
LT2
56
51
56
62
--Date
29
LT2
62
56
59
64
--Country Club
29
LT2
62
57
59
65
---

125
300
430
215
335

Country Club
Robson
Mahoney
Mesa
Udall

22
22
22
15
15

LT2
LT2
LT2
LT3
LT3

63
59
59
65
63

55
52
50
50
48

60
57
57
61
59

65
63
62
66
65

------

------

125
300
430
215
335

Country Club
Robson
Mahoney
Mesa
Udall

22
22
22
15
15

LT2
LT2
LT2
LT3
LT3

63
59
59
65
63

55
52
50
50
48

60
57
57
61
59

65
63
62
66
65

------

------

Notes:
a. Desc.=Type of land use, SFR=single-family residence, MFR=multi-family residence, TLR=trailer park, MHP=mobile
home park/village.
b. Distance to the near track is rounded off to the nearest 5 ft.
c. Ldn values are rounded off to the nearest whole number unless shown otherwise.
d. Based on the measured Ldn, existing noise level was adjusted for distance from Main Street using
10*log(distance). During noise measurements, the dominant noise source at each LT site was traffic on Main Street.
Because noise from traffic would change with distance this conservative existing Ldn estimate was used.
e. Project Ldn is the additional noise that would be created by the LRT operations.
f. Number of Impacts. This is a count of the number of SFR in the cluster plus the estimated number of residential
units in multi-family buildings, rooms in motels/hotels where people sleep and mobile homes/trailers.
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TABLE 12: SUMMARY OF NOISE IMPACT ASSESSMENT FOR CATEGORY 3
Cluster

Desc.a

1
EVIT School
2
Landmark Restaurant
2-Lane Option
3
Childbirth Edu. Class
4
City Hall
Tri-City Community
5
Service Center
6
Pioneer Park
7
Mormon Temple
4-Lane Option
3
Childbirth Edu. Class
4
City Hall
Tri-City Community
5
Service Center
6
Pioneer Park
7
Mormon Temple

Near
Track
Dist.
(ft)
320
85

LRT Exist
Leq, (dBA)
Impact
Speed Noise Existing b Project c
Impact
(mph) Site
Threshold
Mod Severe
33
LT1
63
55
65
70
None
29
LT2
62
60
64
70
None

55
75
60

22
22
22

LT2
LT2
LT3

64
63
64

59
58
59

65
64
65

71
70
70

None
None
None

105
600

15
15

LT3
LT3

68
60

53
56

68
63

73
68

None
None

55
75
60

22
22
22

LT2
LT2
LT3

64
63
64

59
58
59

65
64
65

71
70
70

None
None
None

105
600

15
15

LT3
LT3

68
60

53
56

68
63

73
68

None
None

Notes:
a. Desc.= Type of Land Use.
b. Based on measured daytime Leq at the nearest long-term (LT) site, existing noise level was adjusted for distance
from Main Road using 10*log(distance). During noise measurements, the dominant noise source at each LT site was
traffic on Main Street. Because noise from traffic would change with distance this conservative existing Ldn estimate
was used.
c. Maximum 1-hour Leq during daytime when facility is in use.

TABLE 13: SUMMARY OF NOISE IMPACT ASSESSMENT FOR CATEGORY 1
Cluster

Desc.a

2-Lane Option
-Mesa Arts Center
4-Lane Option
-Mesa Arts Center

Near
Track
Dist.
(ft)

LRT Exist
Leq, (dBA)b
Impact
Speed Noise Existing Project c
Impact
(mph) Site
Threshold
Mod Severe

120

25

LT2

60

57

58

64

None

120

25

LT2

60

57

58

64

None

Notes:
a. Desc.= Type of Land Use.
b. Maximum 1-hour Leq during daytime when facility is in use.
c. Project Leq is the additional noise that would be created by the LRT Operations.
d. The temple lawn is occasionally used for outdoor concerts.

5.1.2 Audible Warnings at Grade Crossings
Train movements at all at-grade crossings will be controlled by signal lights that are
synchronized with Main Street traffic lights. There are no gates or stationary bells for atCentral Mesa LRT Extension
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grade crossings. However, the lead vehicle of the trains would be equipped with bells
and horns that are sounded during emergencies when there is emanate danger and to
avoid accident. The horns would generate a noise level of 102 dBA at 100 ft in front of
the train and the bells would generate 80 dBA at 50 ft in front of the train. For the
analysis of bell noise, the bells are assumed to be sound simultaneously at the front and
rear of the leading vehicle and at the rear of the trailing vehicle. The noise levels are
based on the specifications of the horns and bells installed in light rail vehicles of the
LRT Starter Line.
Because horns would be used only for emergencies, they are an insignificant noise
source and the noise from horns has not been included in the noise assessment. Bells,
however will be sounded by all trains when approaching a crowded station and by
exception at stoplights. The potential impact from bell noise at sensitive receivers that
are located close to train signals and stations are assessed in this study by combining
the bell noise with the noise from the train operations. The results of the impact analysis
are shown in Table 14 through Table 16. Based on the analysis, no noise impacts from
the LRT bells are predicted at any Category 1, 2 and 3 land uses.

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TABLE 14: LRT BELL NOISE IMPACTS AT CATEGORY 2 RECEIVERS
Cluster Desc.a

2
Motel
7
SFR
8
MHP
12
MHP
13A
TLR
14
Motel
16B
Motel
21
Hotel
2-Lane Option
22
Hotel
23
Hotel
24
SFR
25
SFR
4-Lane Option
22
Hotel
23
Hotel
24
SFR
25
SFR

Near Station/ Stoplight b Exist
Ldn, (dBA)
Impact
Track
Noise Existing c Bell d Project Impact Threshold
Dist. (ft)
Site
Noise e
Mod
Severe
50 Longmore Stoplight
LT1
73
57
64
65
72
None
200 Alma School Station LT2
61
48
57
65
72
None
145 Alma School Station LT2
67
50
62 f
62
67
None
160 Alma School Station LT2
67
49
62 f
62
67
None
55 Extension Stoplight
LT2
66
50
60
62
67
None
80 Extension Stoplight
LT2
65
51
60
61
66
None
45 Date Stoplight
LT2
67
50
62 f
62
68
None
145 Country Club Station LT2
62
48
58
59
65
None
125
300
430
215

Country Club Station
Country Club Station
Country Club Station
Mesa Drive Station

LT2
LT2
LT2
LT3

63
59
59
65

52
45
42
48

57
53
51
52

60
57
57
61

65
63
63
66

None
None
None
None

125
300
430
215

Country Club Station
Country Club Station
Country Club Station
Mesa Drive Station

LT2
LT2
LT2
LT3

63
59
59
65

52
45
42
48

57
53
51
52

60
57
57
61

65
63
63
66

None
None
None
None

Notes:
a. Desc.=Type of land use, SFR=single-family residence, MFR=multi-family residence, TLR=trailer park.
b. LRT station or stoplight signal closest to the receiver.
c. Based on the measured Ldn, existing noise level was adjusted for distance from Main Road using 10*log(distance).
d. Projected Ldn from bells attached to the light rail train.
e. Projected Ldn for the combined noise from the bells and light rail train operations.
f. Predicted noise level is rounded off to the nearest integer. The actual noise level is lower than the moderate impact
threshold.

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TABLE 15: LRT BELL NOISE IMPACTS AT CATEGORY 3 RECEIVERS
Cluster

Desc.

2

Landmark
Restaurant
2-Lane Option
3
Childbirth Edu.
Center
4
City Hall
5
Tri-City
Community
Service Center
6
Pioneer Park
4-Lane Option
3
Childbirth Edu.
Center
4
City Hall
5
Tri-City
Community
Service Center
6
Pioneer Park

Near
Track
Dist. (ft)
50

55

Station/ Stop

Exist
Leq, (dBA)
Impact
Noise Existing a Bell b Project
Impact
Site
Noise c Threshold
Mod Severe
Extension Stoplight LT2
62
59
62
64
70
None

75
60

Country Club
Station
MAC Station
Hibbert Stoplight

LT2

64

62

64

65

71

None

LT2
LT3

63
64

60
59

62
62

64
65

70
70

None
None

105

Mesa Drive Station LT3

68

57

59

68

73

None

55

LT2

64

62

64

65

71

None

75
60

Country Club
Station
MAC Station
Hibbert Stoplight

LT2
LT3

63
64

60
59

62
62

64
65

70
70

None
None

105

Mesa Drive Station LT3

68

57

59

68

73

None

Notes:
a. Based on measured Leq, existing noise level was adjusted for distance from Main Road using 10*log(distance).
b. Projected Leq from bells attached to the light rail train.
c. Projected Leq for the combined noise from the bells and light rail train operations.

TABLE 16: LRT BELL NOISE IMPACTS AT CATEGORY 1 RECEIVERS
Cluster

Desc.

2-Lane Option
-Mesa Arts Center
4-Lane Option
-Mesa Arts Center

Near Station/ Stop a Exist
Leq, (dBA)
Track
Noise Existing b Bell c Project
Dist. (ft)
Site
Noise d

Impact
Impact
Threshold
Mod Severe

130

MAC Station

LT2

60

55

58 f

58

64

None

130

MAC Station

LT2

60

55

58 f

58

64

None

Notes:
a. LRT station or stoplight signal closest to the receiver.
b. Based on the measured Leq, existing noise level was adjusted for distance from Main Road using
10*log(distance). During noise measurements, the dominant noise source at each LT site was traffic on Main Street.
Because noise from traffic would change with distance this conservative existing Leq estimate was used.
c. Projected Leq from bells attached to the light rail train.
d. Projected Leq for the combined noise from the bells and light rail train operations.
f. Predicted noise level is rounded off to the nearest integer. The actual noise level is lower than the moderate impact
threshold.

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5.1.3 Ancillary Equipment
Traction power substation (TPSS) units are the only ancillary equipment associated with
the proposed project with the potential to cause noise impacts. A total of three TPSS
units are required along the 3.1-mile alignment. Although only three are required,
several locations are being considered for each of the three major locations (labeled A,
B & C in Table 17). The locations of the TPSS units are shown in the Cluster drawings
in Appendix E. There are seven proposed sites distributed along the project corridor that
have been evaluated as potential sites for the three TPSS units. Several of the selected
sites are adjacent to residential land uses. It is common to include noise limits in the
purchase specifications for TPSS units to minimize the potential for noise impacts from
TPSS noise. The specifications generally include maximum noise limits for potential
noise generators, such as the transformer hum and any cooling systems. The cooling
fans are the major noise source on many modern TPSS units and the transformer hum
is usually inaudible except very close to the TPSS unit.
It is common to have a design goal of limiting noise from TPSS units to be at least 5
decibels lower than the nighttime ambient. This is lower than the FTA noise impact
criteria, but is appropriate because controlling TPSS noise usually is straightforward and
rarely adds more than marginally to the cost. The first step in controlling TPSS noise is
to include a noise limit in the purchase specifications for TPSS units. The recommended
limit is that the maximum noise level not exceed 50 dBA at a distance of 50 feet from
any part of a TPSS unit.
Table 17 shows the predicted levels of TPSS noise at the residence nearest to each of
the sites being considered along with the measured nighttime Leq for the site. A noise
impact is indicated when the predicted TPSS nighttime Leq noise level exceeds the
existing nighttime Leq minus 5 decibels. This approach for assessing TPSS noise
impact is more stringent than the FTA impact criteria and ensures no impacts are
overlooked. As seen in Table 17, mitigation needs to be considered only for TPSS site
A-1. As discussed in Section 6, the mitigation can be as simple as arranging for the
ventilation fans to be on the side of the TPSS building that is farthest from noise
sensitive receptors.

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TABLE 17: PREDICTED TPSS NOISE
TPSS
Unit
Site

Location

Nearest
Residence

Existing Noise Level
(dBA)
Nighttime
Ldn (dBA)
Leq a
54
61
59
66
52
59
52
59
56
63
63
63
63
70

Predicted TPSS
(dBA) b
Leq
Ldn

Impact

A-1
Main & Beverly
20 ft
57
63
Yes
A-4
Main & Extension
50 ft
49
55
No
B-1
Main & Country Club
250 ft
35
41
No
B-3
Main & Country Club
115 ft
42
48
No
B-4
Main & Morris
135ft
40
47
No
C-2
Main & Leseur
360 ft
32
38
No
C-3
Main & Hobson
50 ft
49
55
No
Notes:
a
Nighttime Leq measured between the hours of 10pm to 7am.
b
PredictedTPSS noise is based on a maximum noise level of 50dBA at 50 ft from any part of the TPSS.

5.2

OPERATIONAL VIBRATION

As discussed in Section 3.4, FTA guidelines provide two criteria for assessing vibration
impacts. The first criterion is based on the overall vibration velocity level and is intended
for use with a General Assessment. The key thresholds applicable to the Central Mesa
LRT Extension are a maximum vibration level of 72 VdB for Category 2 (residential)
land uses and 75 VdB for Category 3 (institutional) land uses. The second FTA criterion
is based on the 1/3 octave band spectrum of the predicted vibration. Impacts would
occur if any 1/3 octave band level of the predicted vibration exceeds the impact
threshold. The threshold for residential land uses is 72 VdB over the frequency range of
8 to 80 Hz. This means that an impact would occur if any 1/3 octave band level between
8 and 80 Hz is predicted to exceed 72 VdB. FTA indicates that the second criterion is
intended for use with a Detailed Assessment when vibration propagation testing has
been performed and the predictions include the vibration spectrum. As discussed in
Section 2.2 (Existing Conditions), vibration propagation tests were performed at
four locations in the project corridor. Therefore, it is appropriate to apply the Detailed
Assessment criteria to more accurately identify potential vibration impacts.
After applying the General Assessment criteria for both 2- and 4-lane alternatives,
potential for vibration impact was identified at 10 residential land use clusters and at
four institutional land uses in the project corridor. The number of potential impacts was
reduced considerably after applying the Detailed Assessment criteria. Table 18 and
Table 19 present the vibration impact predictions for the Central Mesa LRT Extension
project. Table 18 shows residential land uses (residences, motels, and trailer parks)
while Table 19 shows institutional land uses (schools, churches, medical facilities, and
parks). The data presented in the tables includes:
x

Description of the property and land use. Single-family residences (SFR), and
multi-family residences (MFR), motels, hotels, mobile home parks and trailer

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parks are the most common Category 2 land uses along the Central Mesa LRT
alignment. The most common Category 3 land uses are churches and parks.
x

The predicted level of LRT vibration. These predictions are for living spaces in
the affected buildings.

x

The applicable FTA impact threshold for a General Assessment. As discussed in
Section 3.4, FTA guidelines include different vibration criteria for a General
Assessment and a Detailed Assessment. General Assessment criteria are singlenumber limits using the overall vibration velocity level, and Detailed Assessment
criteria are curves that the predicted vibration spectrum is compared to.

x

Whether the predicted vibration levels exceed the General Assessment
threshold.

x

Whether the spectrum of the predicted vibration exceeds the applicable Detailed
Assessment criterion curve.

x

Maximum spectral value. The band-maximum level of the 1/3 octave band
spectrum.

As shown in Table 18, potential for vibration impact (detailed assessment) is predicted
at six Category 2 sensitive receivers west of Country Club Drive. It includes three
motels and three mobile home parks. The impacted motels are American Executive Inn,
Motel Rawls, and Motel 6. Apache West Mobile Village and Mesa Gardens Mobile
Home Park are the affected mobile home parks, and Mesa Royale Trailer Park is the
affected trailer park. No vibration impact is predicted at Category 2 land uses east of
Country Club Drive. As shown in Table 19, vibration impact is not predicted at any
institutional land uses. No historic properties identified as listed on the NRHP or
potentially eligible for listing would be adversely impacted by groundborne noise or
vibration due to LRT operations.
In addition to the sensitive receivers listed in Table 18 and Table 19, the Health
Sciences building on EVIT campus and the Ikeda Theater at the Mesa Arts Center
(Special Building) were looked at in detail. The Health Sciences building was evaluated
as a Category 1 land use (sensitive equipment) and the Ikeda Theater has been
evaluated as a “Special Building” (see Table 10, page 40).

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TABLE 18: SUMMARY OF VIBRATION IMPACT ASSESSMENT FOR CATEGORY 2
Cluster Desc. a

1
SFR
2
Motel
3
Motel
4
SFR
5
Motel
6
Motel
7
SFR
8
MHP
9
SFR
10
MFR
11
TLR
12
MHP
13
Motel
13A
TLR
14
Motel
15
SFR
16
Motel
16A
TLR
16B
Motel
17
SFR
18
Motel
19
MFR
20
SFR
21
Hotel
2-Lane Option
22
Hotel
23
Hotel
24
SFR
25
SFR
26
SFR
4-Lane Option
22
Hotel
23
Hotel
24
SFR
25
SFR
26
SFR

Near
Closest
Speed Lv, Impact GA b
Detailed Impact? c
Track Cross Street (mph) (VdB) Thresh. Impact? 1st 2nd
# of
Dist. (ft)
(VdB)
Floor Floor Units d
310
50
50
300
50
50
200
50
140
80
220
50
80
55
80
110
45
45
45
360
60
690
180
145

Longmore
Longmore
Rogers
Rogers
Stewart
Stewart
Alma School
Beverly
Beverly
Extension
Beverly
Beverly
Beverly
Extension
Extension
Extension
Date
Date
Date
Date
Date
Date
Date
Country Club

33
33
33
33
33
33
29
29
29
29
29
29
29
29
29
29
29
29
29
29
29
29
29
29

61.5
79.5
79.5
61.8
79.5
79.5
64.3
78.0
67.8
73.3
63.4
78.0
73.3
77.0
73.3
70.2
79.0
79.0
79.0
58.5
76.2
52.1
65.4
67.5

72
72
72
72
72
72
72
72
72
72
72
72
72
72
72
72
72
72
72
72
72
72
72
72

No
Yes
Yes
No
Yes
Yes
No
Yes
No
Yes
No
Yes
Yes
Yes
Yes
No
Yes
Yes
Yes
No
Yes
No
No
No

-No
No
-No
No
-Yes
-No
-Yes
No
No
No
-No
Yes
No
-No
----

-Yese
---Yesf
------------Yesg
------

-1
---3
-1
---1
-----1
2
------

Max
Spectral
Value
(VdB)
-73.4
---73.4
-72.2
---72.2
-----73.2
73.2
------

125
300
430
215
335

Country Club
Robson
Mahoney
Mesa
Udall

22
22
22
15
15

67.7
59.6
56.2
60.1
56.1

72
72
72
72
72

No
No
No
No
No

------

------

------

------

125
300
430
215
335

Country Club
Robson
Mahoney
Mesa
Udall

22
22
22
15
15

67.7
59.6
56.2
60.1
56.1

72
72
72
72
72

No
No
No
No
No

------

------

------

------

Notes:
a. Desc.=Type of land use, SFR=single-family residence, MFR=multi-family residence, TLR=trailer park,
MHP=mobile home park.
b. GA = General Assessment
c. A safety factor of +3 dB was used for the first floor units. A higher safety factor of +5 dB was used for the
second floor units and mobile homes to account for higher floor amplification of train vibration.
d. Number of impacted units. Note that only units that are within the impact distance and where people sleep
are counted for the vibration impacts.
e. Impacts at second floor units of American Executive Inn.
f. Impacts at second floor units of Motel Rawls.
g. Impacts at second floor units of Motel 6.
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TABLE 19: SUMMARY OF VIBRATION IMPACT ASSESSMENT FOR CATEGORY 3
Cluster a

Desc.

1
EVIT School
2
Landmark Restaurant
2-Lane Option
3
Childbirth Edu. Class
4
City Hall
5
Tri-City Community
Service Center
7
Mormon Temple
4-Lane Option
3
Childbirth Edu. Class
4
City Hall
5
Tri-City Community
Service Center
7
Mormon Temple

Near Speed Lv, Impact
GA b Detailed
Max
Track (mph) (VdB) Thresh. Impact? Impact? Spectral
Dist. (ft)
(VdB)
Value
(VdB)
320
85

33
29

61.1
72.7

75
75

No
No

---

---

55
75
60

22
22
22

75.2
67.8
74.4

75
75
75

Yes
No
No

No
---

----

600

15

54.1

75

No

--

--

55
75
60

22
22
22

75.2
67.8
74.4

75
75
75

Yes
No
No

No
---

----

600

15

54.1

75

No

--

--

Notes:
a. Cluster 6 is Pioneer Park and is intentionally omitted in this table. For parks with only outdoor uses near a
transit project, FTA does not recommend an impact threshold for vibration.
b. GA = General Assessment

Mesa Arts Center: The Mesa Arts Center consists of several buildings bounded by
Main Street to the north, Center Street to the west, and Sirrine Street to the east. The
Mesa Arts Center houses the Ikeda Theater, several studios and office spaces. The
Ikeda Theater is classified as a Special Building by the FTA vibration impact criteria.
The FTA applicable vibration criteria for concert halls is 65 VdB for groundborne
vibration and 25 dBA for groundborne noise. The box office, studios and the office
spaces of the Arts Center complex are less sensitive land uses and have been
evaluated as Category 3 (institutional) land uses.
A vibration propagation test was performed at the theater (refer to site V4 in Section
2.2.2). Accelerometers were placed at the setback distance of the building facing Main
Street, within the box office lobby area of the building, and on the Ikeda Theater
auditorium floor as shown in Figure 25 and Figure 26. The measured LSTM and
coherence are presented in Figure 27. Some key points from the data shown are:
x

The coherence indicates that the valid data range extends from 20 to 100 Hz.

x

The measurement inside the box office indicates more efficient propagation than
in the main auditorium.

x

The LSTM outside the theater is approximately 5 decibels higher than inside the
buildings.

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FIGURE 25: IKE
EDA THEA
ATER MEAS
SUREMENT POSITIO
ON

FIGURE
E 26: MEAS
SUREMEN
NT POSITIO
ON, BOX OFFICE LOB
BBY

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FIGURE 27: MEASURED LSTM AND COHERENCE AT THE MESA ARTS CENTER

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FIGURE 28: PREDICTED VIBRATION AT THE MESA ARTS CENTER

TABLE 20: PREDICTED GROUNDBORNE NOISE AND VIBRATION, MESA ARTS
CENTER
Location

Building Setback (Outside)
Box Office (Lobby)
Ikeda Theater (Inside)

FTA Impact
Predicted Vibrationa
a
Thresholds
GBV, VdB GBN, dBA GBV, VdB GBN, dBA
--63
33
75
-48
-65
25
55
23

Source: FTA Criteria, as applied by ATS Consulting, 2009.
Notes
a. GBV = Groundborne vibration, GBN = Groundborne noise.

Because the predicted vibration of the Ikeda Theater is based on the actual indoor
measurement and the impact line was closer to the building than the future train tracks,
no safety factor was added to the predictions. Figure 28 shows the predicted vibration at
the interior and exterior measurement positions for the maximum train speed of 22 mph.
Table 20 shows the overall groundborne noise and vibration levels based on the
vibration spectra shown in Figure 28. The groundborne noise is the A-weighted
groundborne vibration. This approach for groundborne noise estimation is based on the
FTA recommended assumption that the groundborne noise is equal to vibration. As
shown in Table 20, the predicted groundborne noise and vibration inside the Ikeda

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Theater is below the General Vibration Assessment * thresholds at 22 mph. Although no
impacts are predicted at the Mesa Arts Center, two key factors to consider for the Ikeda
Theater are:
x

In spite of the distance and the mass of the building the transfer mobility shows
relatively efficient vibration transmission into the theater space.

x

The vibration predictions for the theater are based on measurements at one
location on the theater floor.

Because of the above two factors, although the vibration measurements and
assessment indicate that no vibration mitigation would be required for the Ikeda
Theater, a more comprehensive evaluation should be performed during the Preliminary
Engineering phase to confirm this conclusion. The more comprehensive evaluation
should include using an impact line located at the proposed centerline for the near track,
measurements at several locations inside the theater, and measurements of
background vibration and noise during a period when the theater is unoccupied.
Health Sciences Building, EVIT Campus
The Health Sciences building in the EVIT Campus is setback approximately 400 ft from
the south shoulder of Main Street. This building has lab spaces that could house
sensitive equipment and has been considered an FTA Category 1 land use for the
impact assessment. As discussed in Section 3.4, VC-curves are applicable for spaces
with sensitive equipment. The approach used for this analysis was to predict
groundborne vibration at the setback distance of the Health Sciences building based on
the average vibration spectrum for the Central Mesa LRT project shown in Figure 21
and then compare the predicted spectrum to the VC-curves. Given that there is
sensitive equipment within the building, a reasonable goal is that vibration levels should
not exceed the VC-C curve. The predictions in Figure 29 show that the predicted
vibration is below the VC-C curve and therefore no impact is predicted. It is noteworthy
that the predictions are conservative for the following reasons:

*

x

The predictions were for the setback distance of the Health Sciences building.
Because the building is a large structure it is likely that vibration would be
attenuated by 5 to 10 decibels at the location of the sensitive equipment.

x

The predictions are based on the average of vibration propagation tests at sites
V2 through V4. This vibration was significantly higher at 400 ft compared to the
measured vibration at the site V1.

Note that the FTA Guidance Manual (Ref. 1) does not include a Detailed Assessment impact threshold for
Category 1 land uses.
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FIGURE 29: FTA CRITERIA AND PREDICTED VIBRATION FOR EVIT HEALTH
SCIENCES BUILDING

5.3

CONSTRUCTION NOISE AND VIBRATION

5.3.1 Construction Noise
The use of heavy equipment during project construction has the potential to result in
significant, yet temporary, increases in local noise levels along the corridor. The Mesa
noise ordinance prohibits noise from construction during nights and Sundays, but does
not provide limits that can be used to define an impact threshold. The FTA Guidance
Manual does not include any standardized criteria for assessing potential construction
noise levels; however, FTA does provide the guidelines shown in Table 21 for
evaluating the potential community response to construction noise. The guidelines are
based on an average Leq over a typical 8-hour workday. The FTA recommended limit of
80 dBA for the daytime Leq has been used in this assessment as the threshold for
impact for residential areas.

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TABLE 21: CONSTRUCTION NOISE GUIDELINES
Noise Limit, 8hr Leq (dBA)
Land Use
Daytime
80
85
90

Residential
Commercial
Industrial

Nighttime
70
85
90

Source: FTA, 2006.

Construction noise levels depend on the number of pieces and type of equipment, their
general condition, the amount of time each piece operates per day, the presence or lack
of noise attenuating features such as walls and berms, and the location of the
construction activities relative to the sensitive receptors. The majority of these variables
are left to the discretion of the construction contractor. Therefore, it is not possible to
accurately estimate construction noise levels at this stage of the project.
The construction of light-rail track requires use of heavy earth-moving equipment,
pneumatic tools, generators, concrete pumps, and similar equipment. Table 22 shows
the equipment likely to be used during the noisiest periods of track construction, the
typical noise generated by this equipment, the usage factors, and the estimated workshift Leq. The combined work-shift Leq for the construction scenario shown in Table 22
is 84 dBA. Given that residences along the corridor are often within 50 ft of the
alignment, it is clear that there is a high probability that the contractor would exceed the
impact threshold of 80 dBA for the work-shift Leq. This analysis shows that impacts are
likely unless the contractor is required to implement noise control measures when
working in or near residences.
TABLE 22: PREDICTED CONSTRUCTION NOISE
Equipment
Earthmover (bulldozer,
front-end loader, etc.)
Mobile Crane
Dump Truck
Pneumatic Tools
Generator
Compressor
TOTAL:

82 dBA

Usage Factor (%
of time under full
load)
40%

81 dBA
76 dBA
85 dBA
78 dBA
81 dBA

20%
40%
30%
40%
40%

Sound Level @
50 ft under load

Leq (8hr work
shift)
78 dBA
74 dBA
72 dBA
80 dBA
74 dBA
77 dBA
84 dBA

5.3.2 Construction Vibration
Some activities, such as compaction, pavement breaking, and the use of heavy
earthmoving equipment), could result in perceptible levels of groundborne vibration.
However, these activities would be limited in duration and vibration levels are likely to
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be well below thresholds for minor cosmetic building damage. Typical vibration limits
are shown in Table 23. The planned construction would include a limited number of
activities expected to generate vibration that approaches the lowest limit in Table 23.
TABLE 23: CONSTRUCTION VIBRATION LIMITS
Structural Damage
Typical for construction
Extremely fragile buildings
Historic and ancient buildings

PPV
(in/sec)a
2.0
0.2
0.12

Source
Bureau of Mines Bulletin 656, 1971
FTA, 2006
German Standard DIN 4150

Notes:
a) Peak Particle Velocity

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