King County Metro Transit is about to get its first three fully electric buses to test for a year while it decides whether or not to order another 200 over the next five years.

If it decides to exercise the option, it would be the largest order yet for Proterra, the Greenville, South Carolina company leading the charge on electric buses, Greenville Online reports.

Seattle is the tenth city to try Proterra’s zero-emissions alternative, a growing trend that is starting to take off in the world of public transportation.

King County still likes to brag that Seattle was the first major U.S. city to rollout a large fleet of hybrid-electric buses back in 2004, and this is its way of keeping up with the times.

A Metro newsletter from January reports the buses can be fully charged in about 10 minutes, so they could theoretically stay in service 24/7 and charge on the street while passengers are unloading.

A Metro spokeswoman tells GeekWire the buses show promise, but they want to make sure they work well in hilly Seattle before they fully jump onboard.

Metro hasn’t decided yet which routes the test buses will run, but they’ll probably be carrying riders from the east side of Lake Washington into downtown Seattle.

Charging stations are already setup, and the buses themselves should arrive by late summer or early fall. I’m told the new buses will have a special wrap, so they won’t be hard to spot.

Metro used a $4.7 million federal grant to fund the project.