4.5 Environmental Impacts

Transcription

1 Construction impacts are also expected to include air emissions, dust and vibration, as discussed in the DEIR/EA, and there have been no changes to these impacts since the DEIR/EA. 4.5 Environmental Impacts This section describes the potential noise and vibration impacts associated with the proposed College Avenue Station, as a terminal station, as required by the MEPA Certificate Noise Extending the Green Line would add a new noise source to the environment along the proposed corridor. While there is existing noise exposure from sources such as commuter trains and automobiles, introducing an additional noise source and relocating the commuter rail lines have the potential to increase future noise at some noise-sensitive receptors. The DEIR/EA, in the analysis of Alternative 1, evaluated noise levels along the entire route of the Green Line Extension, including noise levels associated with College Avenue Station as a terminal station. Noise impacts are the result of several elements of the Proposed Project: Commuter Rail operations on the track shifted to the east, closer to residences; Green Line operations on the new western tracks; Green Line trains idling on the tail tracks north of the College Avenue Station; and Green Line trains operating on the crossover (turnout) switch at the tail tracks. These noise sources are minor, do not cause potential impacts and are less significant than the noise generated by the commuter trains. As an example, the three residences on Burget Avenue which are closest to the proposed tail tracks, would be exposed to noise (62.1 dba) from stationary trains on the tail tracks, 72.3 dba from Green Line operations, and 74.7 dba from commuter train operations. The total future noise (cumulative noise exposure) would be 76.8 dba. This constitutes a moderate noise impact and is due primarily to commuter train operations. Other receptors on Burget Avenue would be exposed to even lower noise levels from sources associated with College Avenue as a terminal station. College Avenue Station 4-7

2 4.5.2 Vibration Potential vibration impact from the College Avenue Station was assessed using the methods described in the DEIR/EA (Section 5.8, Vibration). This analysis evaluated each vibration-sensitive receptor location taking into account the distances to the future commuter line and Green Line tracks and the presence of any special trackwork (crossovers or turnouts). A crossover on the Green Line tail tracks north of College Avenue Station is the only vibration source that is associated with College Avenue being a terminal station. There would be no vibration impact from Green Line trains near College Avenue Station. A crossover south of College Avenue Station is required regardless of whether College Avenue Station is a terminal station or an intermediate station. No changes to noise and vibration impacts or proposed mitigation have occurred at this crossover location since the DEIR/EA. Potential vibration impact prior to mitigation has been identified for residential receptors at Brookings Street due to the shifting of the commuter tracks beyond the College Avenue terminus station. Future vibration levels from the commuter trains would be 75 VdB (an increase from the existing 69 VdB). Since the commuter tracks would be shifted a similar distance closer to these receptors, whether or not College Avenue is a terminal, future vibration levels would be the same. 4.6 Mitigation Measures This section presents a summary of the proposed mitigation options identified in the DEIR/EA to address adverse environmental impacts associated with construction and operation of the proposed College Avenue Station as the terminus of the Proposed Project. Potential permanent impacts resulting from constructing the station would be mitigated to the extent feasible, as summarized in Table Traffic Mitigation Specific to College Avenue Station, two intersections require physical improvements to mitigate adverse impacts caused by project-related traffic: Boston Avenue at Winthrop Street and Boston Avenue at College Avenue. Impacts at Boston Avenue and Winthrop Street would be mitigated by restriping the Boston Avenue northbound approach (currently a single lane approach) to provide an exclusive left-turn lane and a shared through/right-turn lane. Signal timing and phasing changes would also be implemented. Approximately 12 parking spaces along Boston Avenue would be removed for this College Avenue Station 4-8

3 improvement. It is anticipated that the level of service would improve at this intersection from LOS F to LOS D during the evening peak hour as a result of this mitigation. Impacts to Boston Avenue at College Avenue would be mitigated by widening College Avenue westbound to provide an exclusive right-turn lane and a shared left-turn/through lane. Signal timing and phasing changes at this location would also be incorporated. To accommodate this improvement, the College Avenue bridge over the railroad tracks would be widened. Since the bridge is already slated for reconstruction as part of the Project, changes can be made without additional construction impacts. It is anticipated that level of service would improve at this intersection from LOS F to LOS D during the critical evening peak hour with this mitigation. As shown in Table 4-2, pedestrian mitigation is proposed at six intersections surrounding College Avenue Station. This mitigation ranges from restriping crosswalk markings and increasing pedestrian crossing times to installing pedestrian crossing signals and ADA compliant wheelchair ramps Noise Mitigation Noise mitigation is considered based on the need, feasibility, reasonableness and effectiveness of potential options. The FTA states that in considering potential noise impact, severe impacts should be mitigated if at all feasible. At the moderate impact level, more discretion should be used, and other project-specific factors should be included in considering mitigation. These factors include the predicted increase over existing noise levels, the types and number of noisesensitive land uses affected, existing outdoor-to-indoor sound reduction, and the effectiveness of mitigation options and the cost-effectiveness of mitigating the noise. However, the FTA also states that there is a stronger need for mitigation if a project is proposed in an area currently experiencing high noise levels (Ldn above 65 dba) from surface transportation sources. This is clearly the case at sensitive receptors adjacent to the College Avenue Station where existing Ldn levels range between 70 to 79 dba. In view of this guidance by the FTA, the Project would mitigate both moderate and severe noise impacts wherever feasible and wherever existing noise levels are above 65 dba. Noise impacts will also be mitigated for receptors with no significant outdoor land use if interior day-night sound levels (Ldn) are above 45 dba from project sources or singleevent maximum noise levels (Lmax) above 65 dba. To mitigate noise impact from train operations, noise control can be considered at the source, along the sound path, or at the receiver. Source noise control options, for example, may include special insulating hardware at turnout College Avenue Station 4-9

4 locations, 2 relocating special trackwork away from sensitive areas and using continuous welded rail. Noise barrier construction is the most common sound path noise control treatment, which is being considered for the track alignment, as described in the DEIR/EA. It can be very effective at reducing noise levels in the community. A noise barrier 1,000 feet long, approximately six feet in height on a retaining wall along the right-of-way would be effective in mitigating potential noise impact at receptors on Burget Avenue and Brookings Street. This noise barrier is required whether or not College Avenue is a terminal station. Future noise levels from both commuter and Green Line trains are expected to be reduced nine to 11 decibels with this barrier and future noise levels are expected to be lower than existing levels. Figure 4-6 shows the location of the proposed noise barrier Vibration Mitigation The purpose of vibration mitigation is to minimize adverse effects from a project at sensitive locations. While the consideration of noise mitigation is well-defined, there is more variability in the approach to vibration mitigation and the specific measures that may be considered. The goal for mitigating potential vibration impact from the proposed Green Line Extension Project is to reduce future vibration below the impact criteria, which is 72 VdB for Green Line trains and 75 VdB for commuter trains. At some locations, close to the existing commuter trains, future vibration levels may not be able to be reduced below the impact criterion with reasonable mitigation measures. As stated in the DEIR/EA, these locations were identified as locations with potential residual impacts, however, additional measurements will be conducted in the next phase of Project development and mitigation measures could be refined. At these locations, mitigation measures that will reduce vibration levels 5 decibels or more will be considered reasonable and effective with the intention of keeping future vibration levels at or below existing vibration levels. The effectiveness of specific vibration mitigation measures is dependent on several factors such as the component design, installation techniques, axle loads of the trains and frequencies of concern. Resilient rail fasteners, which are specially-designed fasteners between the rails and the ties, may reduce vibration by 5 to 10 VdB. Ballast mats may be effective in reducing vibration levels 10 to 15 VdB. Generally, well-designed and properly-installed ballast mats or resilient rail fasteners would be effective in reducing vibration levels up to 15 VdB for the Green Line trains and up to 10 VdB for commuter trains, keeping future vibration levels generated from commuter trains at or below existing levels and 2 A turnout is a mechanical device that enables a train to switch from one track to another. College Avenue Station 4-10

5 reducing vibration levels generated from Green Line trains below the impact criterion. Vibration mitigation generally performs better for light rail vehicles because they do not weigh as much as commuter trains. Figure 4-7 shows the vibration mitigation location near College Avenue Station. A total of 250 feet (500 track-feet) of vibration mitigation (location #17) is proposed to mitigate potential impacts at receptors on Brookings Street. This mitigation is required whether or not College Avenue is a terminal station Visual Impact Mitigation The Project would incorporate vegetation in and above fences, trees, and steep slopes on each side of the right-of-way at the College Avenue Station site to minimize the rail corridor s visibility. These would reduce the net loss of vegetation and reduce the visual impact of any tree removal on the neighborhood. The retaining wall design, including any vegetated features, would be developed in the final design for the Proposed Project. The major materials used in the College Avenue Station structure would be masonry, steel and glass. Landscaping would be designed to provide protection from the elements without obscuring visibility. Landscaping would be inviting both to the users of the stations and to the passers-by, using small trees and low shrubs, which are easily maintained. The new College Avenue Station would be visible from their street access points and from nearby bridges. The Proposed Project would require some degree of noise mitigation, as described above, such as noise barriers to protect sensitive receptors such as residences from increases in train noise. Noise barriers would reduce the visibility of the green space surrounding the right-of-way and it would also prevent any further visual impacts by obscuring the trains and rails that would otherwise be visible from residential back yards. There have been no changes to the visual impact mitigation since the DEIR/EA Summary of Mitigation Commitments This section summarizes the proposed mitigation options identified in the DEIR/EA to address adverse environmental impacts associated with construction and operation of the proposed College Avenue Station as the terminus of the Proposed Project. Potential permanent impacts resulting from constructing the station would be mitigated to the extent feasible, as summarized in Table 4-2. MassDOT would be College Avenue Station 4-11

6 responsible for ensuring that all mitigation commitments are implemented. There have been no changes to the impacts analysis or mitigation commitments since the DEIR/EA, but are summarized in Table 4-2. Temporary, short-term impacts from construction activities would be mitigated to the extent feasible. Appropriate construction mitigation measures would be incorporated into the contract documents and specifications governing the activities of contractors and subcontractors constructing elements of the Proposed Project. On-site resident engineers and inspectors would monitor all construction activities to ensure that mitigation measures are properly implemented. Construction mitigation measures for the Proposed Project are summarized in DEIR/EA Table 6-2. College Avenue Station 4-12