Issues with hill braking and on-board heat led the Duluth Transit Authority to pull its new fleet of electric buses from routes on the last day of November.
A hill-hold feature on the buses’ brake systems was not catching in time, and buses taking off uphill were rolling back too far from bus stops and traffic signals.
The buses are in the process of making it back to the streets, but not before passing field tests and updating driver training, said General Manager Phil Pumphrey on Wednesday. While no incidents had occurred because of the issues, pulling the buses was described as a precautionary measure.
"In the abundance of safety, I pulled the buses," Pumphrey said. "We're being very strict about making sure it's a safe product. We won't put out a bus that's unsafe."
The DTA started using the electric buses on routes Nov. 19. The buses were procured through a $6.3 million federal grant to test how electric technology would work in Duluth's cold climate and hilly environment.
The buses were manufactured by Proterra of South Carolina and customized to include a diesel auxiliary heater.
The DTA found that running the primary electric heaters were causing the buses to lose battery life and limiting the expected range of the buses. The fix: the diesel heaters will be brought online as the primary heating source, relegating the electric heat to auxiliary.
The other issue seemed more involved. Pumphrey described the “hill hold” feature on the bus as having too much play when a bus would take off after having stopped on hills either for signals or at bus stops.
"When the buses would stop on an incline going up hill and let people off we thought it needed some more to make it consistent and easier to use," Pumphrey said.
The DTA allows buses to back up 6 inches as they throttle from a stop up a hill. Pumphrey said drivers reported issues with the hill-hold feature on the bus.
"(Proterra) has made a patch - it's a software thing, not a mechanical patch," Pumphrey said. "We agreed it wasn't working. It was rolling back when (drivers) took their foot off the brake and went to the gas. The electric motor wasn't responding (quickly enough)."
The DTA encourages its riders exiting the bus to cross behind the bus. Pumphrey worried that passengers risked being struck or even other vehicles which might have pulled to a stop too close to one of the electric buses. Also, he said he was concerned about on-board riders being jostled during the take-off from a hill stop.
Pumphrey rode one of the buses during a test drive Wednesday following a software update. It yielded positive results.
“The software installation fixes the problem of rollback,” he said. “It works like it should and it’s an improvement.”
Pumphrey expected the buses would be back on routes by next week, or even by the end of the week. He reiterated his safety message, saying, "We want to do the right thing by customers and employees and have a safe vehicle out there and we'll do everything to make that happen."