Metro is aiming to switch to an entirely electric bus fleet by 2045.

The Washington Metropolitan Area Transit Authority Board’s executive committee gave preliminary approval for a plan for the agency to operate only electric buses by 2045 at a meeting Thursday. WMATA’s plan proposes a transition to purchasing hybrid-electric or compressed natural gas buses in the coming years before switching to electric-only buses starting in 2030.

Metro is estimating the plan will cost $900 million to a billion dollars, DCist reported.

The agency currently operates 1,600 buses in over 10 garages—with only one electric so far—and plans to purchase 100 new buses each year, DCist reported.

Environmentalist groups, like the Sierra Club, challenged WMATA to become fully electric by 2045 last October as a part of the Clean Energy D.C. Act’s deadline for zero emissions for public buses.