The TRansportation and Air Quality (TRAQ) research group

Simulating the environmental effects of isolated and network-wide traffic calming schemes using traffic simulation and microscopic emission modelling

This study focuses on the development of a microscopic traffic and emission simulation system which aims at quantifying the effects of different types of traffic calming measures on vehicle emissions both at a link-level and at a network-level. It also investigates the effects of isolated traffic-calming measures at a corridor level and area-wide calming schemes, using a scenario analysis. Our study is set in Montreal, Canada where a traffic simulation model for a dense urban neighborhood is extended with capabilities for microscopic emission estimation.

The results indicate that on average, isolated calming measures increase carbon dioxide (CO2), carbon monoxide (CO), and nitrogen oxide (NOx) emissions by 1.50%, 0.33%, and 1.45%, respectively across the entire network. Area-wide schemes result in a percentage increase of 3.84% for CO2, 1.22% for CO, and 2.18% for NOx. Along specific corridors where traffic calming measures were simulated, increases in emissions of up to 83% were observed, replace 83% by 160%. These increases are mainly associated with a change in vehicle drive-cycles through increased accelerations and decelerations. We also account for the effect of different measures on traffic volumes and observe moderate decreases in areas that have undergone traffic calming. In spite of traffic flow reductions, total emissions do increase. Finally, we observe that speed bumps result in higher emission levels than speed humps.

We also conducted dispersion modelling along selected segments and examined NO2 concentrations resulting from varying levels of NOx emissions under the same traffic calming scenarios. The results indicate that traffic calming measures do not have as large an effect on nitrogen dioxide (NO2) concentrations as the effect observed on nitrogen oxide (NOx) emissions. Changes in emissions can result in highly disproportional changes in pollutant levels due to daily meteorological conditions, road geometry and road orientation with respect to wind direction. We observe that average NO2 levels increase between 0.1% and 10% with respect to the base-case while changes in NOx emissions vary between 5% and 160% along specific segments. Also, the effects of wind speed and direction are investigated in this study. The results show that higher wind speeds decrease NO2 concentrations on both sides of the roadway. As the wind becomes more orthogonal to the roadway, the difference in NO2 levels between the leeward and windward sides increases. Among the traffic calming measures, speed bumps produce the highest increases in NO2 levels.