table of contents...central mesa lrt extension page ii november 2010 draft environmental assessment...

Central Mesa LRT Extension Page ii November 2010 Draft Environmental Assessment Noise and Vibration Technical Report

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�

Central Mesa LRT Extension Page iii November 2010 Draft Environmental Assessment Noise and Vibration Technical Report

6.1� Train Noise .................................................................................................... 70�6.2� Audible Warnings .......................................................................................... 70�6.3� Transit Power Substations ............................................................................ 70�6.4� Train Vibration ............................................................................................... 70�6.5� Construction Noise ........................................................................................ 73�6.6� Construction Vibration ................................................................................... 74�

7.� 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�

Central Mesa LRT Extension Page iv November 2010 Draft Environmental Assessment Noise and Vibration Technical Report

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 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 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-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�


Central Mesa LRT Extension Page v November 2010 Draft Environmental Assessment Noise and Vibration Technical Report


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-4: Clusters Sheet 4, 2-Lane Alternative ........................................................ E-5�



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�

Central Mesa LRT Extension Page vi November 2010 Draft Environmental Assessment Noise and Vibration Technical Report

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 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 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�

Central Mesa LRT Extension Page 1 November 2010 Draft Environmental Assessment Noise and Vibration Technical Report

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


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-of-the-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 No-Build 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, 4-Lane 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.


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-of-way. 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 All day except late evening:

Late evening: 10 minutes 20 minutes

Number of Vehicles 6 – Central Mesa LRT Extension 50 – LRT Starter Line and Northwest LRT 56 – Total fleet

Line-haul Capacity 2,700 passengers per peak hour per direction (Based on 3 vehicles per train and 150 passengers/vehicle)

Hours of Operation 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


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 park-and-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-of-way 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


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 Type of

StationPark-and-

RideBus

Interface Location/

Platform Configuration LRT Facilities (Stations) Sycamore/Main St. (LRT Starter Line End-of-Line Station)

Regional Yes Yes East of intersection Center platform Facility not attributable to LRT extension

Alma School/Main St. 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) Stapley/Main St.1 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 U.S. 60/Power (Superstition Springs Center) 1

Regional Yes Yes North of intersection

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:

� Build Alternative, 2-Lane Option

� Build Alternative, 4-Lane Option


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-and-ride, 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: � On-street parking � Bicycle facilities � TPSS location � OCS � Left turn requirements � Pedestrian access points � Park-and-ride sizing, layout and capacity � Station design � Urban design/public art � Refinement of utilities and location � Construction staging


FIGURE 3: BUILD ALTERNATIVE, SYCAMORE TO COUNTRY CLUB DRIVE


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


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


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


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


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:

� Identify potential sources of noise and vibration.

� 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.

� 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.

� Develop prediction models for each source.

� Determine impact thresholds at each cluster.

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

� 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.


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 pre-existing 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.

� 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.

� 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.

� 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


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.

� 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.

� 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.

� 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.

� 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.

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


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:

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

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

� 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:

� 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.

� 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.

� 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 semi-permanently located mobile homes supported by temporary footings.

� 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.


TABLE 3: SUMMARY OF OPERATIONAL NOISE IMPACT AND MITIGATION

Noise Source FTA Category for Sensitive Land Uses

Exceeds FTA Impact Level

# of Impacted

Units

Mitigation

LRT Operations Category 1 No 0 No Category 2 No 0 No Category 3 No 0 No

Audible Warnings Category 1 No 0 No Category 2 No 0 No Category 3 No 0 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

No. of Impacted

Unitsb

Mitigation Option

West of Alma School Road American Executive Inn 1c Stiffen the floors of the affected unit Motel Rawls 3c Stiffen the floors of the affected units

Between Alma School Road and Extension Road

Mobile Home Park 1 Shift the affected mobile home to 60 feet from the near track centerline

Apache West Mobile Village 1 Shift the affected mobile home to 60 feet from the near track centerline

East of Extension Road Mesa Royale Trailer Park 1 Shift the affected mobile home to 60 feet from the near track centerline

Motel 6 2c Stiffen the floors of the affected unitsNotes: 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.


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


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 24-hour noise measurements and six 15-minute noise measurements. An additional 24-hour 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:

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

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

� 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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TABLE 5: SUMMARY OF EXISTING NOISE MEASUREMENTS

Site Location Type of LandUse

Dur.1 StartTime,

hh:mm

Dist. from Center of Main St.,

ft2

Leq(Day), dBA3

Leq(Night),dBA3

Ldn,dBA3

LT1 1600 W Main St SFR4 24-hour -- 80 69.1 63.8 71.5 LT2 617 W Main St SFR 24-hour -- 80 62.9 57.7 65.3 LT3 456 E Main St Pioneer

Park 24-hour -- 65 67.6 62.5 70.1

LT4 Mesa Arts Center

Theater 24-hour -- 145 58.7 52.7 60.6

M1 1504 W Main St Motel 15-min. 09:31 AM 50 66.5 -- -- M2 1310 W Main St Motel 15-min. 09:57 AM 55 66.0 -- -- M3 951 W Main St Motel 15-min. 10:21 AM 95 64.4 -- -- M4 944 W Main St MFR5 15-min. 10:46 AM 67 63.6 -- -- M5 630 W Main St Motel 15-min. 11:12 AM 50 69.0 -- -- M6 250 W Main St Motel 15-min. 11:42 AM 135 61.1 -- -- M76 2301 W Main St Vacant

Parcel 1-hour 09:17 AM 55 66.3 -- --

M86 NEC Apache Blvd & Smith Rd (Tempe)

Vacant Parcel

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


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 state-of-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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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.


FIGURE 8: LOCATIONS OF VIBRATION PROPAGATION TEST SITES

Source: ATS Consulting, 2009



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FIGURE 11: SITE V3, DOWNTOWN MESA

FIGURE 12: SITE V4, MESA ARTS CENTER


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:

� 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.

� 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.

� 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.

� 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.


FIGURE 13: MEASURED LSTM AND COHERENCE, SITE V1


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


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

Noise Metric (dBA)

Description of Land Use Category

1 Outdoor Leq(h) (1) 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.

2 Outdoor Ldn 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.

3 Outdoor Leq(h) (1) 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.


FIGURE 17: FTA NOISE IMPACT CRITERIA


TABLE 7: FTA NOISE IMPACT CRITERIA

Existing Noise Exposure Leq or Ldn

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<43 Ambient+10 Ambient+15 Ambient+15 Ambient+20 43 52 58 57 63 44 52 58 57 63 45 52 58 57 63 46 53 59 58 64 47 53 59 58 64 48 53 59 58 64 49 54 59 59 64 50 54 59 59 64 51 54 60 59 65 52 55 60 60 65 53 54 60 60 65 54 55 61 60 66 55 56 61 61 66 56 56 62 61 67 57 57 62 62 67 58 57 62 62 67 59 58 63 63 68 60 58 63 63 68 61 59 64 64 69 62 59 64 64 69 63 60 65 65 70 64 61 65 66 70 65 61 66 66 71 66 62 67 67 72 67 63 67 68 72 68 63 68 68 73 69 64 69 69 74 70 65 69 70 74 71 65 70 71 75 72 66 71 71 76 73 66 71 71 76 74 66 72 71 77 75 66 73 71 78 76 66 74 71 79 77 66 74 71 79

>77 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.


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:

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

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

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

� 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.

3.4 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


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 Events

Occasional Events

InfrequentEvents

Category 1. Buildings where vibration would interfere with interior operations. Typically land uses include vibration-sensitive research and manufacturing, hospitals with vibration-sensitive equipment, and university research operations.

65 VdB 65 VdB 65 VdB

Category 2. Residences and buildings where people normally sleep. 72 VdB 75 VdB 80 VdB

Category 3. Institutional land uses with primarily daytime use. 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


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.


FIGURE 18: FTA CRITERIA FOR DETAILED VIBRATION ANALYSIS


TABLE 9: INTERPRETATION OF VIBRATION CRITERIA FOR DETAILED ANALYSIS

Criterion Curve Max Lv1

(VdB) Description of Uses

Workshop 90 Distinctly feelable vibration. Appropriate to workshops and non-sensitive 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, Operating Rooms

72 Vibration not feelable, but groundborne noise may be audible inside quiet rooms. Suitable for medium-power optical microscopes (100X) and other equipment of low sensitivity.

VC-A 66 Adequate for medium- to high-power optical microscopes (400X), microbalances, optical balances, and similar specialized equipment.

VC-B 60 Adequate for high-power optical microscopes (1000X), 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(VdB re 1 micro-inch/sec)

Groundborne Noise Impact 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.


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.


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:

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

� Train speed: 25 mph

� 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:

� �� 3.32sin2log10max ��

�

��

lengthspeedLSEL

where: speed = Velocity in mph length = Length of train in feet (e.g. 2 car LRT = 190 ft) y = Distance from receiver to track centerline �= tan-1(length/2y) Change in sound level with speed:

��

��

1

2log20 speedspeedSEL

where: speed1 = Initial speed speed2 = New speed �SEL = Change in SEL for speed change from speed1 to speed2


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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: � �TLSEL log10max ��

where: T = duration of the maximum bell noise Calculation of Ldn and hourly Leq from SEL:

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:

��

�� DrefDLpLp ref log20

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)

� � 4.4910log10 �� NIGHTDAYDN NTrainNTrainSELL

� � 6.35log10)( �� HOUREQ NTrainSELHourL


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:

��

�� DrefDLpLp ref log20

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


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:

� 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).

� 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).

� 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.


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)


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:

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

� 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.

� 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


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: � 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.

� 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.

� 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.

� 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.


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:

� Cluster: Cluster number.

� Desc: Describes the type of land use.

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

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

� 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.

� 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)).

� 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


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

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

� 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:

� Buildings on the EVIT campus near Longmore.

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

� The City Hall in downtown Mesa.

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

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

� 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:

� 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.

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

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


TABLE 11: SUMMARY OF NOISE IMPACT ASSESSMENT FOR CATEGORY 2

Cluster Desc.a NearTrackDist. b

(ft)

Closest Cross Street

LRT Speed(mph)

ExistNoiseSite

Ldn c, (dBA) # of Impactsf

Existing d Project e ImpactThreshold

Mod Severe Mod Severe1 SFR 310 Longmore 33 LT1 66 55 61 66 -- -- 2 Motel 50 Longmore 33 LT1 73 63 65 72 -- -- 3 Motel 50 Rogers 33 LT1 73 63 65 72 -- -- 4 SFR 300 Rogers 33 LT1 66 55 61 67 -- -- 5 Motel 50 Stewart 33 LT1 73 63 65 71 -- -- 6 Motel 50 Stewart 33 LT1 73 63 65 71 -- -- 7 SFR 200 Alma School 29 LT2 61 56 58 64 -- -- 8 MHP 50 Beverly 29 LT2 67 61.6 62 67 -- -- 9 SFR 140 Beverly 29 LT2 63 57 59 65 -- -- 10 MFR 80 Extension 29 LT2 65 60 62 67 -- -- 11 TLR 220 Beverly 29 LT2 61 56 58 64 -- -- 12 MHP 50 Beverly 29 LT2 67 61.6 62 67 -- -- 13 Motel 80 Beverly 29 LT2 65 60 62 67 -- --

13A TLR 55 Extension 29 LT2 66 61 62 67 -- -- 14 Motel 80 Extension 29 LT2 65 60 62 67 -- -- 15 SFR 110 Extension 29 LT2 64 58 60 65 -- -- 16 Motel 45 Date 29 LT2 67 62 62.3 67 -- --

16A TLR 45 Date 29 LT2 67 62 62.3 67 -- -- 16B Motel 45 Date 29 LT2 67 62 62.3 67 -- -- 17 SFR 360 Date 29 LT2 59 53 57 63 -- -- 18 Motel 60 Date 29 LT2 66 61 62 67 -- -- 19 MFR 690 Date 29 LT2 56 51 56 62 -- -- 20 SFR 180 Date 29 LT2 62 56 59 64 -- -- 21 Hotel 145 Country Club 29 LT2 62 57 59 65 -- --

2-Lane Option 22 Hotel 125 Country Club 22 LT2 63 55 60 65 -- -- 23 Hotel 300 Robson 22 LT2 59 52 57 63 -- -- 24 SFR 430 Mahoney 22 LT2 59 50 57 62 -- -- 25 SFR 215 Mesa 15 LT3 65 50 61 66 -- -- 26 SFR 335 Udall 15 LT3 63 48 59 65 -- --

4-Lane Option 22 Hotel 125 Country Club 22 LT2 63 55 60 65 -- -- 23 Hotel 300 Robson 22 LT2 59 52 57 63 -- -- 24 SFR 430 Mahoney 22 LT2 59 50 57 62 -- -- 25 SFR 215 Mesa 15 LT3 65 50 61 66 -- -- 26 SFR 335 Udall 15 LT3 63 48 59 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.



Cluster Desc.a NearTrackDist.(ft)

LRT Speed(mph)

ExistNoiseSite

Leq, (dBA) ImpactExisting b Project c Impact

Threshold Mod Severe

1 EVIT School 320 33 LT1 63 55 65 70 None 2 Landmark Restaurant 85 29 LT2 62 60 64 70 None

2-Lane Option 3 Childbirth Edu. Class 55 22 LT2 64 59 65 71 None 4 City Hall 75 22 LT2 63 58 64 70 None

5 Tri-City Community Service Center

60 22 LT3 64 59 65 70 None

6 Pioneer Park 105 15 LT3 68 53 68 73 None 7 Mormon Temple 600 15 LT3 60 56 63 68 None

4-Lane Option 3 Childbirth Edu. Class 55 22 LT2 64 59 65 71 None 4 City Hall 75 22 LT2 63 58 64 70 None

5 Tri-City Community Service Center

60 22 LT3 64 59 65 70 None

6 Pioneer Park 105 15 LT3 68 53 68 73 None 7 Mormon Temple 600 15 LT3 60 56 63 68 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.


Cluster Desc.a NearTrackDist.(ft)

LRTSpeed(mph)

ExistNoiseSite

Leq, (dBA)b ImpactExisting Project c Impact


2-Lane Option -- Mesa Arts Center 120 25 LT2 60 57 58 64 None

4-Lane Option -- Mesa Arts Center 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 at-


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.


TABLE 14: LRT BELL NOISE IMPACTS AT CATEGORY 2 RECEIVERS

Cluster Desc.a NearTrack

Dist. (ft)

Station/ Stoplight b ExistNoiseSite

Ldn, (dBA) ImpactExisting c Bell d Project

Noise eImpact Threshold

Mod Severe2 Motel 50 Longmore Stoplight LT1 73 57 64 65 72 None7 SFR 200 Alma School Station LT2 61 48 57 65 72 None8 MHP 145 Alma School Station LT2 67 50 62 f 62 67 None12 MHP 160 Alma School Station LT2 67 49 62 f 62 67 None

13A TLR 55 Extension Stoplight LT2 66 50 60 62 67 None14 Motel 80 Extension Stoplight LT2 65 51 60 61 66 None

16B Motel 45 Date Stoplight LT2 67 50 62 f 62 68 None21 Hotel 145 Country Club Station LT2 62 48 58 59 65 None

2-Lane Option 22 Hotel 125 Country Club Station LT2 63 52 57 60 65 None23 Hotel 300 Country Club Station LT2 59 45 53 57 63 None24 SFR 430 Country Club Station LT2 59 42 51 57 63 None25 SFR 215 Mesa Drive Station LT3 65 48 52 61 66 None

4-Lane Option 22 Hotel 125 Country Club Station LT2 63 52 57 60 65 None23 Hotel 300 Country Club Station LT2 59 45 53 57 63 None24 SFR 430 Country Club Station LT2 59 42 51 57 63 None25 SFR 215 Mesa Drive Station LT3 65 48 52 61 66 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.



Cluster Desc. NearTrack

Dist. (ft)

Station/ Stop ExistNoiseSite

Leq, (dBA) ImpactExisting a Bell b Project

Noise cImpact


2 Landmark Restaurant

50 Extension Stoplight LT2 62 59 62 64 70 None

2-Lane Option 3 Childbirth Edu.

Center 55 Country Club

Station LT2 64 62 64 65 71 None

4 City Hall 75 MAC Station LT2 63 60 62 64 70 None5 Tri-City

Community Service Center

60 Hibbert Stoplight LT3 64 59 62 65 70 None

6 Pioneer Park 105 Mesa Drive Station LT3 68 57 59 68 73 None4-Lane Option

3 Childbirth Edu. Center

55 Country Club Station

LT2 64 62 64 65 71 None

4 City Hall 75 MAC Station LT2 63 60 62 64 70 None5 Tri-City

Community Service Center

60 Hibbert Stoplight LT3 64 59 62 65 70 None

6 Pioneer Park 105 Mesa Drive Station LT3 68 57 59 68 73 NoneNotes: 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.


Cluster Desc. NearTrack

Dist. (ft)

Station/ Stop a ExistNoiseSite

Leq, (dBA) ImpactExisting b Bell c Project

Noise dImpact


2-Lane Option -- Mesa Arts Center 130 MAC Station LT2 60 55 58 f 58 64 None

4-Lane Option -- Mesa Arts Center 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.


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.


TABLE 17: PREDICTED TPSS NOISE

TPSSUnitSite

Location Nearest Residence

Existing Noise Level (dBA)

Predicted TPSS (dBA) b

Impact

NighttimeLeq a

Ldn (dBA) Leq Ldn

A-1 Main & Beverly 20 ft 54 61 57 63 Yes A-4 Main & Extension 50 ft 59 66 49 55 No B-1 Main & Country Club 250 ft 52 59 35 41 No B-3 Main & Country Club 115 ft 52 59 42 48 No B-4 Main & Morris 135ft 56 63 40 47 No C-2 Main & Leseur 360 ft 63 63 32 38 No C-3 Main & Hobson 50 ft 63 70 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:

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


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.

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

� 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 single-number limits using the overall vibration velocity level, and Detailed Assessment criteria are curves that the predicted vibration spectrum is compared to.

� Whether the predicted vibration levels exceed the General Assessment threshold.

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

� 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).


TABLE 18: SUMMARY OF VIBRATION IMPACT ASSESSMENT FOR CATEGORY 2

Cluster Desc. a NearTrack

Dist. (ft)

Closest Cross Street

Speed(mph)

Lv, (VdB)

ImpactThresh.(VdB)

GA b

Impact?Detailed Impact? c Max

Spectral Value(VdB)

1stFloor

2ndFloor

# of Units d

1 SFR 310 Longmore 33 61.5 72 No -- -- -- -- 2 Motel 50 Longmore 33 79.5 72 Yes No Yese 1 73.4 3 Motel 50 Rogers 33 79.5 72 Yes No -- -- -- 4 SFR 300 Rogers 33 61.8 72 No -- -- -- -- 5 Motel 50 Stewart 33 79.5 72 Yes No -- -- -- 6 Motel 50 Stewart 33 79.5 72 Yes No Yesf 3 73.4 7 SFR 200 Alma School 29 64.3 72 No -- -- -- -- 8 MHP 50 Beverly 29 78.0 72 Yes Yes -- 1 72.2 9 SFR 140 Beverly 29 67.8 72 No -- -- -- -- 10 MFR 80 Extension 29 73.3 72 Yes No -- -- -- 11 TLR 220 Beverly 29 63.4 72 No -- -- -- -- 12 MHP 50 Beverly 29 78.0 72 Yes Yes -- 1 72.2 13 Motel 80 Beverly 29 73.3 72 Yes No -- -- --

13A TLR 55 Extension 29 77.0 72 Yes No -- -- -- 14 Motel 80 Extension 29 73.3 72 Yes No -- -- -- 15 SFR 110 Extension 29 70.2 72 No -- -- -- -- 16 Motel 45 Date 29 79.0 72 Yes No -- -- --

16A TLR 45 Date 29 79.0 72 Yes Yes -- 1 73.2 16B Motel 45 Date 29 79.0 72 Yes No Yesg 2 73.2 17 SFR 360 Date 29 58.5 72 No -- -- -- -- 18 Motel 60 Date 29 76.2 72 Yes No -- -- -- 19 MFR 690 Date 29 52.1 72 No -- -- -- -- 20 SFR 180 Date 29 65.4 72 No -- -- -- -- 21 Hotel 145 Country Club 29 67.5 72 No -- -- -- --

2-Lane Option 22 Hotel 125 Country Club 22 67.7 72 No -- -- -- -- 23 Hotel 300 Robson 22 59.6 72 No -- -- -- -- 24 SFR 430 Mahoney 22 56.2 72 No -- -- -- -- 25 SFR 215 Mesa 15 60.1 72 No -- -- -- -- 26 SFR 335 Udall 15 56.1 72 No -- -- -- --

4-Lane Option 22 Hotel 125 Country Club 22 67.7 72 No -- -- -- -- 23 Hotel 300 Robson 22 59.6 72 No -- -- -- -- 24 SFR 430 Mahoney 22 56.2 72 No -- -- -- -- 25 SFR 215 Mesa 15 60.1 72 No -- -- -- -- 26 SFR 335 Udall 15 56.1 72 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.


TABLE 19: SUMMARY OF VIBRATION IMPACT ASSESSMENT FOR CATEGORY 3

Cluster a Desc. NearTrack

Dist. (ft)

Speed(mph)

Lv, (VdB)

ImpactThresh.(VdB)

GA b

Impact?DetailedImpact?

MaxSpectral

Value(VdB)

1 EVIT School 320 33 61.1 75 No -- -- 2 Landmark Restaurant 85 29 72.7 75 No -- --

2-Lane Option 3 Childbirth Edu. Class 55 22 75.2 75 Yes No -- 4 City Hall 75 22 67.8 75 No -- -- 5 Tri-City Community

Service Center 60 22 74.4 75 No -- --

7 Mormon Temple 600 15 54.1 75 No -- -- 4-Lane Option

3 Childbirth Edu. Class 55 22 75.2 75 Yes No -- 4 City Hall 75 22 67.8 75 No -- -- 5 Tri-City Community

Service Center 60 22 74.4 75 No -- --

7 Mormon Temple 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:

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

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

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



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


FIGURE 28: PREDICTED VIBRATION AT THE MESA ARTS CENTER

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

Location FTA Impact Thresholdsa

Predicted Vibrationa

GBV, VdB GBN, dBA GBV, VdB GBN, dBA Building Setback (Outside) -- -- 63 33 Box Office (Lobby) 75 -- 48 -- Ikeda Theater (Inside) 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


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:

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

� 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:

� 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.

� 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.


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.


TABLE 21: CONSTRUCTION NOISE GUIDELINES

Land Use Noise Limit, 8hr Leq (dBA)

Daytime Nighttime Residential 80 70 Commercial 85 85

Industrial 90 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 work-shift 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 Sound Level @ 50 ft under load

Usage Factor (% of time under full

load)Leq (8hr work

shift)

Earthmover (bulldozer, front-end loader, etc.)

82 dBA 40% 78 dBA

Mobile Crane 81 dBA 20% 74 dBA Dump Truck 76 dBA 40% 72 dBA Pneumatic Tools 85 dBA 30% 80 dBA Generator 78 dBA 40% 74 dBA Compressor 81 dBA 40% 77 dBA

TOTAL: 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


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 PPV(in/sec)a Source

Typical for construction 2.0 Bureau of Mines Bulletin 656, 1971 Extremely fragile buildings 0.2 FTA, 2006 Historic and ancient buildings 0.12 German Standard DIN 4150

Notes: a) Peak Particle Velocity

table of contents...central mesa lrt extension page ii november 2010 draft environmental assessment...

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