When you hear “EV”, you tend to think of a car, but the term is a big umbrella. E-bikes and scooters fall under the category as well, and so do buses. Public transit is already a fairly sustainable choice. Given the large size of bus battery packs and their pre-existing efficiency for mass transportation, does switching buses to electric appreciably lower emissions? Is it worth the work and cost of adding commercial charging infrastructure?
Our first stop in answering these questions was the Joint Office of Energy and Transportation. This specialized government group supports the electrification of public transit by providing resources and technical assistance to local agencies.
They tell us that over the lifetime of a single battery electric bus, total greenhouse gas emissions are estimated at 1,192 short tons versus 2,112 short tons for a diesel equivalent. That’s a difference of over 40% and a strong argument for electric buses on climate impact alone.
The Joint Office of Energy and Transportation pointed us to the AFLEET online tool, which provides estimations for all sorts of transit emission scenarios. For example, a single all-electric transit bus operating in the District of Columbia has an estimated fuel economy of 11.2 miles per diesel gallon equivalent (MPDGE), while a diesel transit bus is estimated at 4.4 miles per gallon (MPG). Getting more than twice the mileage for the emissions is pretty dang good.
Beyond greenhouse gas emissions are local emissions. People using public transit are exposed to all sorts of particulates. The American Lung Association says we can mitigate pediatric asthma attacks and infant deaths by reducing exposure to direct transportation emissions. The adoption of zero-emission vehicles could cumulatively amount to $978 billion in public health benefits, 89,300 fewer premature deaths, 2.2 million fewer asthma attacks, and 10.7 million fewer lost workdays. These benefits would be equitable too, since lower-income people are more likely to be riding the bus.
As for charging, DC fast chargers can be centralized at bus depots where they can be well-maintained. Electric buses use chargers that are similar to those for consumer vehicles, which minimizes technological hurdles. That said, additional charging stations across service areas are required for buses to maintain consistent uptime, and bus routes need to be adjusted accordingly.
Public transit is just the first stop on electrifying buses, however. School buses move a lot more people on a daily basis. In the U.S., over 25 million kids ride the bus every day. Set schedules with big breaks in between provides predictability for school bus charging and grid demand. Bus batteries are so big that their potential contribution in vehicle-to-grid energy on this timetable is promising. Through schemes like that provided by Zum in Oakland, school buses can help power homes during peak evening hours when the grid is under the most strain. These buses can even start paying back their up-front cost through net metering, whereby schools earn credit on their electrical bills by feeding power back into the grid when it’s needed most.
As we look for success stories, it’s hard to ignore China.
“They have about half a million EV buses on the road now. That suggests we could be doing more in this space. I would not be surprised if China is 80% of the world’s electric bus fleet.” says Christopher Knittel.
Christopher Knittel is from the Center for Energy and Environmental Policy Research at MIT. He’s an economist who has spent a lot of time looking at costs, challenges, and opportunities around transit electrification. Sure enough, his take on China is accurate. The last tally in 2022 put China’s count of pure electric buses at around 455,500, which was 64.8% of the global share at the time. By comparison, the U.S. had a little over 6,000 battery electric buses in 2023.
Shenzhen is particularly noteworthy. This tech hub on the border of Hong Kong is where many of our favourite gadgets are built. Local expertise has been equally applied to electrify their entire 16,000-bus fleet, and that was seven years ago. Since then they’ve also completely electrified their taxi fleet. This shows that it can be done, but it requires a lot of government support.
Bumps in the road
Why haven’t we flipped the switch already and electrified America’s bus fleets?
For one, we have to wait on the gas-guzzlers to retire. Municipalities have spent good money on the buses they have, and with tight budgets, it makes no financial sense to retire them while they’re still functional. As of 2021, about 22% of the American bus fleet was eligible for retirement, which isn’t a bad chunk to start with.
Even once diesel buses are retired, electric alternatives still cost upwards of three times more than their fossil fuel counterparts. That’s a hard pill to swallow, even with long-term savings in fuel and maintenance costs. It would take $8.5 billion to replace the 22% of the bus fleet that was ready to go as of 2021 and another $2.0 to $3.1 billion to replace the three to four thousand buses retiring each year until 2035. On the flip side, Chicago’s transit authority estimates that they would save about $25 million in annual costs with a fully converted fleet.
Climate also impacts EV performance. Batteries get unstable when subjected to high temperature, requiring extra energy be spent on cooling. That extra energy can put a 25% dent into range, depending on conditions. One rollout in Albuquerque was stalled due to buses failing to perform under the heat, though there were other issues, and the city went on to expand their electrified fleet. Meanwhile, Indianapolis needed to install additional wireless charging stations to make up for the range shortfall caused by cold.
What’s the next stop?
When asked about how to improve U.S. adoption of electrified fleets, Knittel’s hopes lay with policy changes.
“I would love to see more federal guidance on this. We can leave it up to municipalities. We can leave it up to the states. We can leave it up to school districts. But there’s potentially a lot of economies of scale here. Unless we have market coordination across states and cities, we’re just not going to have access to the cheapest and best technologies.”
The state of New York has already enacted a mandate to shift to electric school buses, and California has similar legislation for public transit transitioning completely by 2040. New tax credits in the Inflation Reduction Act provides some federal-level incentives for commercial EVs and charging infrastructure, plus about $1.5 billion is being provided in direct electrification funding. It will take time to see the impact of this funding. It’s a good start, but there’s still a long road ahead.