Since 2004, a startup in the Silicon Valley has been working on finding a way to fuel buses without using diesel—a liquid fuel that emits nitrogen oxide pollutants. The company, Proterra, sold 62 buses in 2015 but faced a logistical obstacle: the vehicle needs to be recharged after 146 miles.

On Monday, the startup introduced a new variation of their electric bus that can be more seamlessly embraced, as it has the same driving capacity as a diesel bus. Proterra's Catalyst E2 can be on the road for 18 hours without needing to charge up.

"The first generation of the long-range vehicles we brought out wasn’t good enough for the market," Matt Horton, Proterra's vice president of sales, told Business Insider. "It just couldn’t do all of the routes out there, and frankly, there aren’t any electric buses out there that can today."

To make a 40-foot bus capable of driving 350 miles with 77 passengers on a single charge, Proterra worked on improving the battery—which they build at their offices. Horton told Business Insider that the company created batteries with 660 kWh of energy and placed the newly improved batteries “underneath the body of the bus so it helps [them] keep it very, very low center of gravity.” Proterra also modified the body of the bus by using a carbon fiber composite to ensure both a lightweight design and durability.

With over 300 pre-sold buses, there is no doubt of a demand for the diesel-free vehicle. According to the U.S. Environmental Protection Agency, diesel exhaust can have a detrimental effect on human health. And while environmentally diesel engines produce less carbon dioxide than petrol engines, they emit higher levels of air pollutants.

"This is the first time that an electric vehicle has been brought to market that, on a truly no compromise basis, is going to replace all the fossil fuel vehicles in its category," Horton said.