Metro passed a major hurdle Wednesday in its campaign to extend its rail system to Dulles Airport.
The Federal Transit Administration has approved plans for the proposed 23-mile project.
Earlier this year, the FTA said the expansion project did not meet federal cost-efficiency standards. That designation jeapordized $900 million in necessary federal funding.
The extension is expected to cost $5-point-2 billion when finished.
The Dulles Rail Project, dubbed the silver line, calls for two phases for the expansion; the first would run from Falls Church through Tysons Corner to Reston. The final phase would extend the metro rail system all the way to Dulles Airport and Loudoun County.
Proponents say the project would lighten traffic congestion for the ever-expanding northern Virginia. Opponents say the project is too expensive and that other options should be considered.