The Société de transport de Montréal (STM), the city's urban transit authority, plans to make its network completely electric by 2040 by adding 140 electric buses to its fleet annually to meet this target. It's an ambitious goal, made more challenging by the extreme swings in the city's weather every year.
The city's cold winters make serious demands on battery electric buses (BEBs). Keeping temperatures comfortable for passengers, accounting for stop-and-go city traffic and managing icy roads are important factors the agency must consider when forecasting its energy consumption as it transitions away from gas-powered vehicles.
A new Concordia-led study provides empirical evidence on how cold weather affects BEB performance while offering data-driven insights into how Montreal and other cities can keep the buses running efficiently year-round.
The research, published in Transportation Research Part D, is based on more than 66,000 data points supplied by the STM from 40 electric buses operating across 56 routes in Montreal. The real-world operational data allowed the team to assess how factors like temperature, traffic and driving patterns influence energy use, regenerative braking and operating costs.
"Most studies on electric buses have focused on temperate regions, but cold weather introduces unique challenges," says primary author Xuelin Tian, who completed her PhD at Concordia this year. Tian is now a postdoctoral fellow at Université Laval in Quebec City.
"We already had a relationship with the STM. Thanks to our previous research, we were able to partner with them for an in-depth analysis of their operational data."
Xuelin Tian: "Most studies on electric buses have focused on temperate regions, but cold weather introduces unique challenges."Lower costs despite winter demands
Unsurprisingly, the study found energy consumption was highest during the winter months, while efficiency was highest during the summer. Energy use peaked at 1.7 kilowatt hours per kilometre (kWh/km) in winter. That figure was roughly 26 per cent higher than in summer, when smoother traffic flow and lower heating and other energy demands helped reduce consumption to 1.4 kWh/km. Spring and autumn fell in between these seasonal extremes.
The researchers also studied regenerative braking, the system that captures energy during deceleration and feeds it back into the battery. Montreal's BEBs recovered an average 45.8 per cent of their braking energy - a figure that rises to more than 50 per cent in the summer.
They performed worst in February, when only 32 per cent of braking energy was recovered. This outcome was due to lowered battery efficiency and icy roads, which forced drivers to rely on traditional friction brakes. Regenerative brakes worked best when the buses were moving at moderate speeds, between 30 to 50 kilometres per hour.
Overall, however, the researchers found that electric buses are far more economical than diesel or hybrid vehicles. Operating costs for electric buses averaged 40 to 60 per cent lower than their diesel counterparts, potentially saving the agency up to $3,500 a day for comparable routes.
"These results can provide improvements in operation planning by optimizing charging strategies, adjusting route lengths and balancing fleet usage," Tian says.
"Aside from helping the STM improve efficiency for their service, our study provides the kind of evidence-based results that can inform future pilot programs in other cities."
Study co-authors include Chunjiang An, associate professor of Building, Civil and Environmental Engineering; PhD candidate Shuyan Wan; Zhikun Chen, PhD 24; He Peng, PhD 25; Mingyu Zhai at Villanova University; and Bobin Wang at Université Laval.
This research was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Fonds de recherche du Québec - Nature et technologies (FRQNT).
