Road Traffic Impact on Pedestrian Exposure to Air Pollution and Noise: A Natural Experiment

Noise and air pollution pose health risks for active transportation users, yet the impact of traffic volume and roadway proximity remains underexplored. This study exploited an unusual circumstance, a natural experiment, to assess environmental changes from temporary road closures. On summer weekends, the National Capital Commission (NCC) of Canada closes a segment of Queen Elizabeth Driveway in Ottawa. To evaluate the environmental benefits of this intervention, measurements of A-weighted equivalent continuous sound levels (LAeq), particulate matter (PM2.5), and ultrafine particles were taken at 12 fixed sites along a nearby multi-use pathway across 10 sampling sessions, over six days. All measured pollutants showed statistically significant reductions during closures. A composite noise–air pollution index indicated a 60% decrease in overall exposure, highlighting the effectiveness of the car-free policy in improving environmental quality for active transportation.