Integrated Multimodel Evaluation of Transit Bus Emissions in Toronto, Canada

Abstract

This paper investigates transit bus emissions in the city of Toronto, Ontario, Canada, by linking the results of a microsimulation transit assignment model, MILATRAS (microsimulation learning-based approach to transit assignment), with emission factors derived from Mobile6.2C. Emissions were estimated at the level of individual buses during idling conditions at bus stops and on roadway links between stops during the morning peak period. The busiest routes were associated with the highest total emissions as a result of a combination of high ridership and lower speeds; this association confirmed the common wisdom that newer, low-emitting buses should be first allocated to these routes. The highest dwell emissions occurred at intermodal transfer stations (bus to subway and vice versa). On a passenger kilometer basis, the highest-emitting routes were not the busiest, but rather were those with the lowest ridership. In fact, the highest emissions per passenger kilometer were associated with the Airport Rocket, a route that provided service to the airport and was characterized by low ridership in the morning peak period. On average, bus trips in Toronto were about three times more fuel efficient than were private car trips and created 20 times less carbon monoxide pollution. The effects of changing fuel types and fleet age on transit bus emissions were assessed. Implications for bus operations are discussed relative to fleet allocation to minimize total emissions.