VDOT Hampton Roads Crossing Study Supplemental Environmental Impact Statement

I-495/I-90 Interchange Improvements Project

This project involved significant realignment of the ramps in the I-495/I-90 interchange in Hopkinton, Southborough, and Westborough, Massachusetts. Its goal was to improve the flow of traffic following the removal of the toll plaza.

HMMH evaluated the potential noise and air quality impacts along the I-495 and I-95 corridors. The noise analysis study area included single- and multi-family residential and recreational noise-sensitive land use as well as a hospital adjacent to the roadways undergoing improvements. For the three Design Year Build alternatives evaluated, traffic noise levels were predicted to approach or exceed the FHWA Noise Abatement Criteria (NAC) at 17 to 36 residences, depending on the alternative. None of the other land uses would be exposed to noise impacts under any of the Build alternatives. HMMH evaluated the feasibility and reasonableness of noise barriers in each area where noise impact were predicted to occur with the Build alternatives. For two of the three Build alternatives, one noise barrier for an apartment complex was found to meet MassDOT’s criteria for both feasibility and reasonableness.

The air quality analysis consisted of evaluating carbon monoxide (CO), mobile source air toxics (MSATs), and greenhouse gas (GHG) emissions for the Build Alternative. HMMH conducted a CO hot-spot analysis for the interchange using the EPA MOVES and CAL3QHC models for compliance with the NAAQS. Using the latest FHWA guidance for MSATs, a qualitative analysis was conducted for the Build Alternative. HMMH also conducted a mesoscale analysis to calculate the potential regional air quality impact of the Project using as a measure the total daily emissions of volatile organic compounds (VOCs), oxides of nitrogen (NOx), GHG, and CO within the project area based on traffic volumes in the area and MOVES emission factors. The mesoscale assessment of GHGs was also used to address the MEPA Greenhouse Gas Emissions and Protocol.