This guest post was authored by Christof Spieler.

It makes sense that many elected officials, advocates, and agency leadership and agency leadership are pushing for electric buses. In addition to the climate benefits, they’re quieter and don’t have any exhaust fumes. There’s also an unprecedented amount of money available through the Bipartisan Infrastructure Law/IIJA for agencies to electrify their bus fleets. Electric buses aren’t the most effective way for transit to help the climate — getting people out of cars is. Still, there’s no doubt electric buses are good.

But when I talk to people who plan, schedule, and operate transit systems they’re really worried about the push for electrification, and for good reason. I’ve heard about three big issues with converting bus fleets to battery electric buses.

The first issue is infrastructure. Battery electric buses need to charge, and a full charge takes a few hours, not a few minutes like a diesel bus. That requires lots of chargers at every bus garage. Agencies often require one for every bus; while it might be possible to swap buses out of charging spaces once they are finished charging, that requires additional staff on the overnight shift and increases safety risks. Chargers take up space between the rows of parked buses. Sometimes, installing them requires moving things at the bus garage; sometimes, it requires more land. 

If an agency wants to charge the buses during the day, it needs chargers at transit centers and end of line layovers, too. Transit centers probably weren’t designed to have the space for electrical gear and the structural capacity for overhead chargers, so retrofits can be complex. End of line locations are often on public streets, where the city might not allow a charger. Daytime electric rates are also often much higher than nighttime rates.

Every one of those chargers needs electricity. The utility feed to a bus garage wasn’t designed to charge dozens of buses at once. So going electric often requires the utility adding more power lines feeding into the facility. (Fun fact: one agency I know of ran into this on their electric bus pilot and ended up having to bring in a diesel generator to charge the electric buses for the test period.) Thus, converting to electric is a major construction project. It’s not just the fleet, it’s infrastructure.

The second issue is reliability. In theory, electric buses should require less maintenance than diesel buses, which are complicated beasts. But this is new technology. 

An electric bus is different from a diesel bus. It has a different kind of drivetrain and a set of big, heavy batteries instead of a diesel tank. That results in completely different weight distribution, which impacts the frame, too. And while we now have experience with electric cars on the road, buses are different — they have to put up with a lot of abuse and last 12 years at maybe 40,000 miles a year.

There are two types of manufacturers in this business. One is the established bus manufacturers adding electric models. They know how to build a durable bus. But they’re fitting electric into bodies designed for diesel. More fundamentally, they’re having to learn new things in a company culture built around slowly refining existing designs. The second is new manufacturers. They’re built around innovation, and they’re designing new buses from a blank sheet around electric batteries and drives. But they don’t have the experience of knowing how to design all the parts of a bus – not just the drivetrain but the rest of mechanicals, the doors, even the inside fixtures — to put up with the rigors of daily service. So both kinds of manufacturers are on a fast learning curve, and it shows. 

Experiences vary hugely, but a lot of agencies have found that electrics are often not as reliable as they expect, with more breakdowns on the road and more time in the shop. This is exacerbated by the change required within the agency. Transit mechanics know how diesel works; we have decades of experience embedded in every bus garage. Diesel has quirks, but they’re known quirks. It will take time for agencies to get that same knowledge for electricity. Right now, agencies are struggling to hire and retain mechanics; electrification can put more burden on an already stretched workforce. Diesel also comes with a built up supply chain (though of course that breaks down sometimes.) Agencies know where to get parts, the manufacturers have support networks in place, and component suppliers are generally well-established. That’s still building up for electric buses. 

So far, battery electric buses are generally not yet proving to be as reliable as diesel buses. And the most important thing every agency has to do is pull the buses out in the morning to start service.

The third issue is scheduling. Ideally, agencies would charge a bus overnight, then run it all day and charge it the next morning. Then, charging is merely an infrastructure issue — if they have enough chargers they’re fine. 

But today’s battery electric buses don’t yet have the range to handle all the duties today’s diesel buses do. For smaller agencies with a limited span of service, it often works. But big urban agencies have buses that pull out at 5:00 am and run to past midnight. A battery bus can’t do that yet. That’s never all the buses in a fleet – every agency has some runs that can be readily converted – but it is an issue for full electrification.

A seemingly obvious solution to limited range is charge during the day, when the bus is paused somewhere. That takes more infrastructure but theoretically it could solve the problem. But that takes time in the schedule. We have layovers built into bus schedules, but those are designed to let late buses recover time. The schedule might show a bus waiting at the end of the line for 15 min, but if it’s 10 min late it’ll have only 5 min. If we want to make sure we have charging time, we need to build in more time, and that either means having more buses to run the same service, or running less service with the same number of buses.

The other solution is to pull buses back into the garage when the battery runs low and pulling in another bus. That still adds to staffing requirements, though – someone needs to drive the bus back – and it requires a spare bus.

So either we have to build time into the schedule for charging, or we have to pull buses into the garage before the end of the day. In either case, we need more buses to do the same work. I’m hearing from some agencies that they need 150 or more battery electric buses to do the work of 100 diesels. Agencies have always needed spare buses; it’s typical to have an extra 20 buses in the garage (some being worked on, others in reserve for breakdowns) for every 100 buses on the road at rush hour. But an electric fleet can require even more, since some of the buses that were out for morning rush may have their batteries drained by the time afternoon rush hour comes around. That obviously increases purchase cost. It could also require building more bus garages since many agencies are already running as many buses as their current garages can fit.

In an ideal world, battery electric buses would be a one-for-one drop in replacement for diesels. They’re not. Electrification requires major infrastructure, electric buses are sometimes less reliable than the buses they replace, and running electrics can require schedule adjustments or a larger fleet. We should see improvement on all these fronts: time and money solves infrastructure, reliability gets better over time, and better technology with longer range could fix scheduling issues. There is also an alternate technology – trolleybuses powered by overhead wires – that is already operating reliably and has no schedule impacts, but it, too, requires significant infrastructure investments. 

Today, though, electrifying bus fleets requires considerable budget, and it takes concerted attention from agency staff and management. And, at the end of the day, even if it goes well, the agency is simply operating the same service it was before – not necessarily more frequent or reliable service, which is what riders care most about. Electrification is good, but there are also many other things agencies need to be focusing on. 

This is perhaps the greatest risk of mandates for fleet conversion: without additional funding, they can actually lead to less frequent and less reliable bus service, and even with additional funding they can distract agencies from improving their service. Electric is the future, and agencies should be making plans for it. But they are right to be cautious about ambitious plans for rapid fleet conversion.