Noise and Vibration Impact Assessment MBTA Green Line Extension Project

Transcription

1 Noise and Vibration Impact Assessment MBTA Green Line Extension Project Presentation to Green Line Extension Advisory Group St. Clements High School Medford, MA December 1, 2008 Jason Ross, P.E. Harris Miller Miller & Hanson Inc.

2 Potential Noise Impact Summary Potential noise impact WITHOUT mitigation would occur generally at: Locations within 100 feet east of the existing commuter rail tracks where the commuter tracks would be relocated closer to receptors Tracks may move up to 13 feet closer to homes Noise would generally increase 1 to 3 decibels Locations within 50 feet of the proposed green line tracks, west of the alignment Noise would generally increase 1 to 2 decibels Locations without any existing train noise Noise would generally increase 2 to 13 decibels Locations near tight-radius curves due to potential for wheel squeal

3 Noise Mitigation Summary Noise Barriers Noise would be reduced 7 to 14 decibels Future noise levels would be substantially lower than existing noise levels 6 to 12 feet in height 14,750 feet in length Estimated cost is $3.5 million Sound Insulation At locations where noise barriers are not feasible or effective North Point Properties -- Visiting Nurses Association Glass Factory Condominiums -- Tufts Science and Technology Center Hampton Inn Hotel -- Tufts Art Studio Brickbottom Lofts -- Tufts Bacon Hall Apartment complex on Pearl St -- Walnut Street Center Rail Lubrication Curve at Somerville Avenue and Prospect Street

4 Noise Impact Assessment and Mitigation Details Orchard Street Existing Noise Level: 71 (Ldn) Future Noise Level Without Mitigation: 74 (Ldn) Potential Increase: 3 decibel (due to relocated commuter tracks) 10-foot Noise Barrier Mitigation: 11 dba reduction Future Noise Level With Mitigation: 63 (Ldn)

5 Noise Impact Assessment and Mitigation Details Tufts University Science and Technology Center and Outside the Lines Art Studio Existing Noise Level: 77 (Leq) Future Noise Level Without Mitigation: 80 (Leq) Potential Increase: 3 decibel (due to relocated commuter tracks) Sound Insulation Mitigation: Increase noise reduction of windows by 5 decibels or more Future Noise Level With Mitigation: Goal is to keep maximum interior noise levels from transit sources below 65 dba

6 Noise Impact Assessment and Mitigation Details Alston St Existing Noise Level: 74 (Ldn) Future Noise Level Without Mitigation: 79 (Ldn) Potential Increase: 5 decibel (25 feet from proposed Green Line) 7-foot Noise Barrier Mitigation: 17 dba reduction Future Noise Level With Mitigation: 62 (Ldn)

7 Noise Impact Assessment and Mitigation Details Somerville Ave and Prospect Street (near curve) Existing Noise Level: 66 (Ldn) Future Noise Level Without Mitigation: 75 (Ldn) Potential Increase: 9 decibel (due to potential wheel squeal) Rail Lubrication Mitigation: Reduce noise by 7 decibels Future Noise Level With Mitigation: 68 (Ldn)

8 Potential Vibration Impact Summary Potential vibration impact WITHOUT mitigation would occur generally at: Locations within 60 feet east of the existing commuter rail tracks where the commuter tracks would be relocated closer to receptors Locations within 40 feet west of the proposed green line tracks

9 Vibration Mitigation Summary Track Treatments Ballast mats or resilient rail fasteners effective in reducing vibration 10 VdB 19,700 track-feet of track treatments Estimated cost is $3.5 million (ballast mats) / $5.9 million (resilient fasteners) All Green Line and commuter tracks located on a boat section a 3-foot thick concrete slab - may also provide additional vibration reduction Relocation or Specially-Engineered Special Trackwork Turnouts and crossovers cause local increases in vibration of up to 10 VdB 12 turnouts and crossovers contribute to potential vibration impact Crossovers may be relocated away from sensitive receptors Flange-bearing or moveable-point frogs can be used to minimize potential vibration impact

10 Vibration Impact Assessment and Mitigation Details Piggot Road Existing Commuter Level: 67 VdB Future Commuter Level: 65 VdB Future Green Line Level: 82 VdB (includes contribution from crossovers) Mitigation: Green Line track treatments and relocation or use of moveable-point frog crossovers

11 Vibration Impact Assessment and Mitigation Details Brookings St Existing Commuter Level: 69 VdB Future Commuter Level: 75 VdB Future Green Line Level: 60 VdB Mitigation: Commuter line track treatments

12 Vibration Impact Assessment and Mitigation Details Nashua St, Hinckley St Existing Commuter Level: 81 VdB Future Commuter Level: 95 VdB (includes contribution from crossovers) Future Green Line Level: 58 VdB Mitigation: Commuter line track treatments and relocation or moveablepoint frog crossovers

13 Vibration Impact Assessment and Mitigation Details Brickbottom Lofts Future Green Line Level: 77 VdB Mitigation: Green Line track treatments No vibration impact near Lechmere Station, Somerville Ave or Prospect St