In the world of electric vehicles, range anxiety has long been the great bugaboo.

For all its benefits—from zero emissions to no worries about gas prices—zipping around on battery power still raises the specter of running out of juice distressingly far from a charging station.

But now, a California company says it has made a major breakthrough—an electric bus that can travel up to 350 miles on a single charge. In fact, on a test track, that vehicle was able to go 600 miles on one charge, says Matt Horton, senior vice president of sales for Proterra, the firm that designed and built the range-busting bus.

So, is this the death knell for loud, smelly diesel buses spewing smoke around city streets?

A battery as big as a mattress

Not yet…but things seem to be moving in that direction.

Right now, only about 5 percent of public buses in the U.S. are battery-powered. But Horton says the percentage is rising quickly and should hit 10 percent soon. Proterra’s CEO, Ryan Popple, has gone so far to suggest that by 2030, every public bus in America could be electric.

Proterra’s accomplishment will likely accelerate the transition. Existing Proterra buses can cover about 150 miles on one charge, not quite enough in some cities to make it through a long day of turning and stopping and starting. “There were few electric buses out there that could make it through the typical 18-hour day that a lot of diesel buses do,” says Horton. “Now we have one that can do that easily.”

It takes about three and a half hours to fully charge one of the buses overnight.

The key for Proterra was not trying to repurpose a standard steel bus with an oversized battery. Instead, the company built a new model from scratch, using a carbon fiber frame that results in a vehicle that’s several thousand pounds lighter than a diesel bus. It’s also equipped with a battery pack—about the size of a twin bed mattress—that’s mounted low under the bus, far away from passengers.

Proterra’s new model also takes advantage of what’s known as regenerative braking. When an electric or hybrid vehicle slows down, the motor runs in the opposite direction, and the mechanical energy of the car’s movement is converted into electrical energy that’s then used to charge the batteries. That not only allows a vehicle to extend its range, but it also reduces wear on its brakes because the driver doesn’t have to apply as much pressure to stop it.

Picking up speed

Probably the biggest challenge facing Proterra is that electric buses still cost considerably more than traditional diesel models and hybrids. A new Proterra bus lists at just under $800,000, almost 50 percent higher than a diesel vehicle and about 25 percent more than a hybrid. That can mean sticker shock for local transit operations that have based their budgets on spending at diesel levels.

So Proterra has gotten creative in helping municipalities deal with the daunting price tag. They might, says Horton, pay upfront the same amount as they would for a diesel bus, then finance the difference. Another option is to buy the bus at a reduced rate, and then just lease its battery. “It’s kind of a monthly service fee,” he says. “It looks like a fuel cost, but it’s actually less than what they’re spending on diesel fuel.”

Horton notes that in addition to helping transit authorities track down federal grants that could help lighten their financial burden, Proterra has spent a lot of time educating potential customers on the long-term benefits of going electric.

“We estimate that it costs about 19 cents per mile to run a Proterra bus, and that compares to about 84 cents per mile for diesel,” he says. “From a maintenance standpoint, our vehicle costs about 50 cents a mile, compared to about $1.10 a mile for diesel. These public buses are often driven 40,000 to 50,000 miles a year, so the savings build up.”

The effort appears to be paying off. Each year of the past three, the company’s sales volume has doubled, according to Horton. It now has sold 315 of its electric buses to 36 different locations around the U.S. That includes 45 of the new buses with the 350-mile range that was just unveiled a few weeks ago. The first of those “E2" models should be on the road in Pomona, California by the middle of next year.

It’s reached the point where Proterra has had to scale up production to keep up with demand. Horton says the company’s plant in Greenville, South Carolina is booked with orders into 2018, so Proterra will be opening another factory near Los Angeles early next year, allowing it to triple its capacity.

Proterra isn’t alone in tapping into the potential of electric buses. The Chinese company, BYD, one of the largest electric vehicle firms in the world, is expected to build as many as 6,000 electric buses this year, including 300 at its plant in Lancaster, California. It is supplying 85 buses to the transit authority in Antelope Valley, north of Los Angeles, which in 2018, will become the first all-electric public bus fleet in America.

Not surprisingly, Horton sounds bullish about the future. “The cost of batteries continues to drop. The technology is getting better and better. I really think that in 10 years, the game will be over for fossil fuels in public transit,” he says. “I just don’t think you’ll see any transit operators betting on diesel again. Our vehicles perform better, and you get clean air, zero emissions and no noise for free.”

He also takes issue with the suggestion that only well-off, “green” communities will fully embrace electric vehicles.

“We have sold buses to Stockton, California; Reno, Nevada; Lexington, Kentucky; and Tallahassee, Florida—places you wouldn’t necessarily think of as wealthy. We’re very proud of that. We’ve found good reception everywhere,” Horton says.

“We have three customers in Texas,” he adds. “If you can sell electric vehicles in Texas, you can sell them anywhere.”