Impact Assessment Methodology for the. Somerville Public Library August 4, 2008 Jason Ross, P.E. Harris Miller Miller & Hanson Inc.

Transcription

1 Noise and Vibration Impact Assessment Methodology for the MBTA Green Line Extension P j t Project Presentation to the Advisory Group Meeting Meeting Somerville Public Library August 4, 2008 Jason Ross, P.E. Harris Miller Miller & Hanson Inc.

2 Presentation Outline Background Noise and vibration basics Types of noise and vibration sensitive locations Impact criteria Noise and vibration projections Potential mitigation options Questions

3 Background Noise and vibration impact is assessed using the Federal Transit Administration (FTA) Guidance Manual 1 These guidelines specify how to measure, evaluate and predict noise and vibration levels from transit sources. These guidelines were developed by Harris Miller Miller & Hanson Inc. Transit agencies are required to follow these assessment guidelines for all Federally-funded projects. 1 Transit Noise and Vibration Impact Assessment, Final Report FTA-VA prepared p for the U.S. Federal Transit Administration by Harris Miller Miller & Hanson Inc., May 2006.

4 Noise and Vibration Basics The basic measure of noise is the A-weighted noise level measured in decibels (dba) Quiet urban areas may have ambient noise levels of 40 to 55 dba Maximum noise levels from automobiles at 50 feet and 50 mph are typically about 70 to 75 dba.

5 Noise and Vibration Basics Lmax maximum noise level Easy to understand Does not take into account duration, number of events, or time of day Ldn equivalent day-night sound level 24-hour level with a nighttime lt penalty At residences or other places where people sleep Leq hourly equivalent sound level During 1-hour period of peak transit operations At locations with daytime use (schools, libraries, museums, ms etc.) Both Ldn and Leq take into account the duration and number of Both Ldn and Leq take into account the duration and number of events, Ldn accounts for nighttime noise

6 Noise and Vibration Basics

7 Noise and Vibration Basics Ground-borne vibration Vibrations are the rapid fluctuation of building surfaces or rattling of windows. Measured in decibels, but not the same decibel as noise. Vibration is measured in terms of the velocity of moving surfaces and are labeled (VdB).

8 Noise and Vibration Basics The basic measure of vibration is the vibration velocity level in decibels (VdB) The limit at which humans can feel vibrations in buildings is about 65 VdB Vibration levels over 100 VdB are needed to cause physical damage to structures The number of events that occur determine the criteria

9 studios Noise and Vibration Basics Ground-borne noise Produced when the vibrations of the floors, ceiling and walls of a building act like a loudspeaker and radiate noise. This noise sounds like a low-frequency rumble. Generally Generally, ground-borne borne noise is only a concern if trains are in a tunnel (no airborne ib paths) or for very sensitive facilities such as concert halls or recording

10 Noise and Vibration Sensitive Locations Noise and vibration impact is assessed at: Locations where people sleep (Category 2) Residences, hospitals, motels and hotels Institutional land uses (Category 3) Schools, libraries, museums, theatres, places of worship Special buildings (Category 1) Recording studios, concert halls, auditoriums, i TV studios Only noise impact is assessed at: Outdoor land uses where quiet is important (Category 1) Outdoor amphitheatres, National Historic Landmarks, parks where quiet is essential to their use Only vibration impact is assessed at: Vibration sensitive equipment (MRIs, Electron Microscopes) Noise and vibration impact are not assessed at: Noise and vibration impact are not assessed at: Commercial or industrial land uses

11 Noise and Vibration Sensitive Locations Sensitive locations along proposed MBTA Green Line gp Extension: H Hampton Inn t Hotel Walnut Street Center (Union Square) Somerville Community Access TV Studio (Union Square) Somerville High School Somerville Public Library Visiting Nurses Associations Assisted Living Tufts University Classrooms Residences Si Science and dt Technology Center Bray Laboratories Nanotechnology Lab

12 Noise and Vibration Impact Criteria Noise and vibration impact criteria for transit projects is specified by the FTA. Noise criteria were developed from well-documented research on human response to community noise Vibration criteria are based on International Standards Organization (ISO) standards and experience with passenger transit operations Noise impact is assessed by comparing existing noise to future noise with the project. As existing noise levels increase, a smaller increase in the future noise levels is allowed. Two levels of noise impact: moderate or severe

13 Noise and Vibration Impact Criteria

14 Noise and Vibration Impact Criteria

15 Noise and Vibration Impact Criteria Land Use Category GBV Impact Levels (VdB re 1 micro-inch /sec) GBN Impact Levels (db re 20 micro Pascals) Frequent Events 1 Occasional Events 2 Infrequent Events 3 Frequent Event 1 Occasional Events 2 Infrequent Events 3 Category 1: Buildings where vibrations would interfere with interior operations. 65 VdB 4 65 VdB 4 65 VdB 4 N/A 4 N/A 4 N/A 4 Category 2: Residences and buildings where people normally sleep. 72 VdB 75 VdB 80 VdB 35 dba 38 dba 43 dba Category 3: Institutional land uses with primarily daytime use. 75 VdB 78 VdB 83 VdB 40 dba 43 dba 48 dba Notes: 1. "Frequent Events" is defined as more than 70 vibration events of the same source per day. Most rapid transit projects fall into this category. 2. Occasional Events is defined as between 30 and 70 vibration events of the same source per day. Most commuter trunk lines have this many operations. 3. "Infrequent Events" is defined as fewer than 30 vibration events of the same kind per day. This category includes most commuter rail systems 4. This criterion limit is based on levels that are acceptable for most moderately sensitive equipment such as optical microscopes. Vibration sensitive manufacturing or research will require detailed evaluation to define the acceptable vibration levels. Ensuring lower vibration levels in a building often requires special design of the HVAC systems and stiffened floors. 5. Vibration-sensitive equipment is generally not sensitive to ground-borne noise.

16 Noise and Vibration Impact Criteria

17 Noise and Vibration Projections Document existing levels Measure vehicle source levels Model noise and vibration levels Assess impact Determine locations for mitigation, if required

18 Noise and Vibration Projections Existing noise measurements at 16 sites along proposed corridor Existing vibration measurements at Tufts University (MBTA Commuter, Amtrak) Vibration propagation characteristics at 3 sites along corridor Reference noise and vibration measurements of Green Line vehicle D Branch near Beaconsfeld Station Station D Branch near Woodland Station

19 Noise and Vibration Projections Existing noise levels LT-1 39 Horace Street (Somerville) LT-2 5 Alston Street (Somerville) LT Medford Street (Somerville) LT-4 34 Richdale Street (Somerville) LT-5 86 Vernon Street (Somerville) LT-6 95 Boston Avenue (Somerville) LT-7 7/9 Winchester Place (Somerville) LT Burget Avenue (Medford) LT-9 76 Orchard Street (Medford) ST-1 Water St (Cambridge) Hampton Inn Hotel ST-2 Fitchburg St (Somerville) Brickbottom Lofts ST Somerville Avenue (Somerville) ST-4 2 Charlestown Street (Somerville) ST-5 45 Aldrich Street (Somerville) activity ST-6 81 Hinckley Street (Somerville) ST-7 Colby Street (Medford) Tufts University Source: HMMH, ST-1, ST-3 - no existing train

20 Noise and Vibration Projections MBTA green line train reference levels 2-car trains, 50 feet, 50 mph Noise (Lmax) ~ 84 dba Noise Vibration (Lmax) ~ 71 VdB MBTA commuter train reference levels 1 locomotive and 4-6 cars, 50 feet, 50 mph Noise (Lmax) ~ 95 to 100 dba Vibration (Lmax) ~ 86 VdB

21 Noise and Vibration Projections Modeling of future transit operations includes: Specific vehicle type Vehicle speeds Track design (continuous welded rail, turnouts, crossovers)

22 Noise and Vibration Projections Modeling of future transit operations includes: Over-ground sound propagation Effects of intervening objects (barriers, berms, buildings) Effects of elevated structures Along several areas the alignment is in a cut Near Lechmere station the alignment is on elevated structure Near Lechmere station the alignment is on elevated structure Vibration propagation characteristics of soil and buildings

23 Noise and Vibration Mitigation Noise mitigation options Source noise mitigation Rolling noise - maintenance (wheel truing, rail grinding) Rolling noise - skirts over trucks Wheel squeal - resilient wheels Wheel squeal - vibration dampers for wheels Wheel squeal - rail lubrication / friction modifiers Horn and crossing bells - quiet zones (horns and grade crossing bells are not expected under normal operation) Impact noise - specific location of special trackwork (crossovers, turnouts) Path noise mitigation Noise barriers (could be extensions to retaining walls) Receiver noise mitigation (rare) Sound Insulation

24 Noise and Vibration Mitigation Vibration mitigation options Maintenance Wheel truing Rail grinding Specific location of special trackwork (crossovers, turnouts) Use of continuous welded rail vs. jointed rail Trackform design Resilient rail fasteners Ballast mats Resili iliently supported ties Floating slabs

25 www hmmh com