Cap the Cross-Bronx? Modeling the Air Quality Impacts of the Proposed Highway Cap

Abstract

Highways pose several environmental, health, and social concerns. The air and noise pollution from vehicles pose a health risk to those living near highways, often disproportionately affecting marginalized communities. One solution to mitigate these negative externalities is highway capping—constructing lids above highways for conversion into deck parks. A highway capping project was recently proposed for the Cross-Bronx Expressway, but little research has been done on its environmental impact, as it is still in the ideation phase. Thus, this thesis uses a differential analysis to assess how the proposed Cross-Bronx Expressway cap would impact air quality in the surrounding area. Using a Gaussian equation model and verifying results through AERMOD, the Environmental Protection Agency’s regulatory atmospheric dispersion model, pollutant concentrations were calculated in areas adjacent to the proposed cap for the no-build and build scenarios. The study found that air quality marginally improves in areas directly adjacent to the cap, but worsens in areas close to the cap exits, particularly the east exit. While the cap keeps PM2.5 and CO concentrations within the National Ambient Air Quality Standards (NAAQS), it exacerbates existing high NOx concentrations near the cap exits. These findings reveal that there is high variation in how community members will be impacted, depending on their proximity to the cap exits.