Air Quality at Bus Stops

Congested traffic corridors in dense urban areas are key contributors to the degradation of urban air quality. While waiting at bus stops, transit patrons may be exposed to greater amounts of vehicle-based pollution, including particulate matter (PM), because of their proximity to the roadway. Current guidelines for the location and the design of bus stops do not take into account air quality or exposure considerations. This study compared the exposure of transit riders waiting at three-sided bus stop shelters that either faced the roadway traffic or faced away from the roadway traffic. Shelters were instrumented with air quality monitoring equipment, sonic anemometers, and vehicle counters. Data were collected for 2 days at three shelters during both the morning and the afternoon peak periods. Bus shelter orientation was found to significantly affect concentration of four sizes of PM: ultrafine particles, PM₁, PM_2.5, and PM₁₀. Shelters with an opening oriented toward the roadway were consistently observed to have higher concentrations inside the shelter than outside the shelter. In contrast, shelters oriented away from the roadway were observed to have lower concentrations inside the shelter than outside the shelter. The differences in PM concentration were statistically significant across all four sizes of particulate matter studied. Traffic flow was shown to have a significant relationship with all sizes of particulate concentration levels inside bus shelters. Microscale anemometer measurements were made next to bus shelters. Both wind speed and direction were shown to affect particulate concentrations differently, depending on shelter orientation.