They’re symmetric and kinetic. They’re also electric. Four new electric buses are now rolling through Iowa City streets.
“Transit in Iowa City has been here since 1971, and this is the first paradigm shift in vehicle technology that there has been, so we are on nerdy levels excited about it,” said Transportation Director Darian Nagle-Gamm.
The red, orange and white buses run smoothly, and create little noise apart from the shuffling of passengers and the tires rolling across the pavement.
Electric vehicles require less energy than fossil-fuel vehicles to cover the same distance, and the price of electricity is more stable than gasoline or diesel. The city’s standard diesel buses produce around 230,000 pounds of greenhouse gas emissions per year. The ZX5 electric buses will reduce emissions by 95 percent, Nagle-Gamm said.
The electricity that powers the buses is eco-friendly, too. Around 57.3 percent of Iowa’s electricity comes from wind. MidAmerican Electric supplies power for Iowa City, and in 2020, 83.6 percent of its power came from renewable sources, mostly wind.
Beyond reducing the city’s carbon footprint, the electric buses will save the city money over its lifespan, according to Nagle-Gamm, who explained Iowa City Transit waited until the cost of electric buses matched or fell below the cost to own and operate diesel buses before purchasing them.
“Electric bus prices are starting to come down pretty significantly from what they were a few years ago,” she said. “It’s cheaper to fuel the buses, but also there’s less labor required to maintain them because you don’t have an engine, and you don’t have a transmission.”
Iowa City purchased the buses, including the charging equipment, using $3.3 million in grants from the Federal Transit Administration and the Iowa Department of Transportation, and $1.2 million from the city’s own funds. Nagle-Gamm said they will continue applying for grant funding to buy electric buses.
Currently, the city has 23 diesel buses, which will be replaced as they age out of service, but the process will take a few decades. The lifespan of a diesel bus is 12 to 20 years, and the city purchased 11 of its diesel buses between 2016 and 2018.
The city bought the ZX5 electric buses from a California-based automotive and energy storage company, Proterra. The company claims that the ZX5 has the most battery storage of any 40-foot electric bus, giving the buses the ability to travel approximately 300 miles per charge.
In cold temperatures, however, electric vehicles can lose range. To offset these losses, the city’s electric buses have an auxiliary diesel-powered heater for the cabin’s interior.
“These auxiliary heaters can help really maximize the amount of battery power that is reserved just for propelling the bus, and not for keeping it warm for passengers on board,” Nagle-Gamm said. “So during the cold weather months, we will use a bit of diesel to help, you know, heat the passenger cab, and then the rest of the year, we won’t need it.”
Iowa City Transit is currently compiling data to determine the electric buses’ range per charge. Each bus route has different energy requirements — depending on how hilly the roads are, how many stops the bus makes, how many passengers board the bus, length of the route, etc. — but Proterra estimates a 15 to 35 percent reduction during cold weather. Without the auxiliary heater, it would be a 25 to 45 percent reduction.
“The great thing about launching them in the coldest days of the year is we will be most impacted weather wise by the range right now,” Nagle-Gamm said.
Iowa City Transit selected the bus model with the most battery capacity, so it expects the electric buses to run all day on a single charge. The buses will then be charged overnight while there is no transit service.
Despite the cold, the new buses have been operating without problems, according to Nagle-Gamm. The lithium battery sits beneath the passengers’ feet, which increases the buses’ overall stability, especially in snowy and icy conditions. The battery placement also makes the buses bottom heavy, so they’re less likely to roll over during crashes and collisions.
“I think they handle better in the snow, because part of the benefit of an electric-powered vehicle is that you can deliver power to each wheel individually, and that is a huge benefit in slippery conditions,” the transportation director said. “They are a supremely comfortable ride and very smooth.”
The buses use Proterra-branded fast chargers. At the moment, Iowa City Transit is using a “temporary setup” that takes around six hours to fully charge the batteries. But the final installation in March will charge the buses within three to four hours.
In addition to traditional hydraulic brakes, which use friction between brake pads and rotors to decelerate, the ZX5 buses have a regenerative braking system. The electric motor stops supplying power when you take your foot off the throttle, causing the vehicle to slow down immediately. The kinetic energy typically lost through friction is converted back into electricity and stored in the battery.
The batteries carry warranties for the buses’ lifespan, which is set at approximately 12 years. But as the buses retire, the batteries will live on.
“Not only are they recyclable, they are actually reusable, too,” Nagle-Gamm said.
Some departments and agencies are using the batteries as back-up power. Iowa City Transit, for example, has a back-up diesel generator that provides power in emergency situations like a derecho. Nagle-Gamm said they can use these batteries to help power their facilities.
The electric buses are one goal in Iowa City’s Climate Action Plan, which calls for net-zero emissions by 2050. The city has lowered its total CO2e emissions from 1,374,712 tonnes in 2010 to 705,303 tonnes in 2020, a 48.7 percent decrease.
“It’s been multiple years in the making, so we’re really excited to finally have them out in service and piloting them in the community,” she said. “We hope the public gets as excited as we are about it.”
The electric buses will operate on the Downtown Shuttle and Oakcrest routes for now. They will move to other routes in the future, except the 10 – West Iowa City route, which has a low-clearance railroad bridge the electric buses cannot fit under.