A new study by researchers at Cornell University, in collaboration with Tompkins Consolidated Area Transit (TCAT), shows that electric bus energy consumption increases significantly in cold weather, particularly in areas with hilly terrain and harsh winters like Ithaca, New York.
The research stems from a pilot program TCAT launched in 2021, funded by a federal grant, to test seven electric buses across 41 different routes in Tompkins County. During the colder months, both the range and performance of the buses were found to be problematic.
To understand the cause, researchers analyzed real-world data and developed “Optimal Temperature Zone” (OTZ) models, which represent the buses’ energy consumption under ideal temperatures (16°C to 30°C). They found that when temperatures dropped to between -4°C and 0°C, the buses consumed about 48% more energy than predicted by the OTZ models. Even within a broader temperature range of -12°C to 10°C, energy consumption was still 28.6% higher.
The study identified two main culprits for this increased energy use. Half of the extra energy was consumed just to heat the batteries themselves. The bus batteries perform optimally at around 24°C, so in cold weather, they require significant power to preheat before the bus can even start.
The other major factor was the cabin heating system, especially on urban routes where frequent door openings allow cold air to enter. “For an all-electric vehicle, the battery is the only onboard energy source,” said Max Zhang, a professor at Cornell and senior author of the study. “Everything depends on it.”
The research also found that regenerative braking, which recharges the battery as the bus decelerates, is less effective in cold conditions. This is partly because the massive batteries—about eight times the size of a typical EV battery—are difficult to keep uniformly warm.
To mitigate these issues, the researchers suggest short-term solutions like parking buses indoors, charging them while the batteries are still warm, and minimizing the time doors are open at stops. On a larger scale, cities may need to rethink their public transit infrastructure, including the number of charging stations, providing heated garages, and adjusting routes and schedules.
“You need to try to optimize the scheduling of all your buses and think about the infrastructure’s capacity,” said Jintao Gu, a doctoral student and the study’s lead author. The team also noted that rural routes, with fewer stops, consumed less extra energy in cold weather than urban routes, which could help transit agencies better allocate their electric buses during winter months.