Powering electric buses comes with special challenge: Which batteries do you buy?
As King County Metro expands its fleet of electric buses with a goal of becoming carbon neutral by 2040 with a zero-emissions fleet, the agency must make important choices about battery size and composition. It’s a puzzle many big transit agencies are working on.
25-year-old Erica Eggleton, a student working on her Ph.D. in chemical engineering at the University of Washington, has developed a model to help transit authorities anywhere in the world make good choices. The tool, called Route Dynamics, is available on Github.
Eggleton admits she’s a bit of a transit fanatic, which she says is because she lived in Europe when she was in middle and high school.
“I loved riding the train and the bus in Germany -- it gave me so much independence. And then I came back to the U.S. in college and didn't have that anymore,” she says.
She lived first in Bozeman, Montana, where she says she mostly had to rely on a personal vehicle to get around. She then moved to Seattle for her doctorate and was excited to be able to take the bus to get where she needs to go. She wants to use her engineering skills to help address the climate crisis. And her passion is creating tools to improve transit.
"Helping bring that to more communities around the U.S. and making it equitable and sustainable for any city,” she says.
Chemical engineering professor Dan Schwartz says King County Metro approached the Clean Energy Institute, which he directs, looking for help choosing batteries.
“Metro wants to buy buses. They just did 40. And they have to decide how big of a battery should we buy?"
He says it’s a question any electric-vehicle owner has to answer: What are the best materials and systems to generate the kind of power they need?
“So, if they buy a 456 kilowatt-hour battery, which routes can that serve? How big of a bus battery, because the price matters.”
He assigned Eggleton to the case. She found that most public transit agencies maintain public data on their bus fleets, such as elevation gain, ridership, acceleration and deceleration along the routes.
“Imagine going up a hill, and if you're doing that on a bike, that is a lot harder for you, right? It's also a lot harder for a bus,” Eggleton says. “Instances like that, that are more stressful, can lead to degradation."
The open-source software tool she designed is so far being used only by King County Metro. But with more and more transit agencies switching to electric fleets because of the need to reduce emissions that cause climate change, the idea is to make it work for transit agencies anywhere in the world.
Schwartz says they’ve also had interest from Portland’s bus system, TriMet.