A school system outside Washington is poised to become the nation’s biggest operator of electric school buses. The Board of Education in Maryland’s Montgomery County voted unanimously on Tuesday evening to approve a 16-year, $169 million contract to lease 326 buses, part of a plan that could result in the county replacing its entire 1,422-bus fleet over the next two decades.

The deal represents the largest municipal government order of any kind for buses, according to Monique Harris, a spokeswoman for Advanced Energy Economy, a business association that promotes clean energy use.

The Biden administration has pledged to support the adoption of electric vehicles and automakers have said they intend to convert their fleets to electric in coming decades. The U.S. Postal Service announced earlier Tuesday a 10-year contract to replace as many as 165,000 vehicles with ones that have either fuel-efficient engines or are powered by batteries.

Essie McGuire, associate superintendent of operations for the Montgomery County school system, said during the Board of Education meeting that the idea of increasing the electrification of the school bus fleet had been under discussion for some time.

“There was some hope for a while that we would be able to perhaps secure a very small number through, perhaps, some grant funds,” she said. “But as time has gone on, we really wanted to take a more ambitious approach.”

Plug-in car supporters say they hope the deal becomes a template for school districts and government agencies across the country.

The vehicles will be built by Thomas Built Buses Inc. and Proterra Inc. in a deal coordinated by Highland Electric Transportation Inc. Todd Watkins, the transportation director of Montgomery County Public Schools, said the contract would be the first electric school bus contract in the nation that is not dependent on federal grants.

Highland will provide buses, install charging facilities at the county’s bus depots and train drivers. The company will also provide maintenance and manage the charging operation.