Metro officials are eyeing a Brown Line to join the system’s existing palette. The transit agency is planning for the future, looking at creating a train line that dips from Friendship Heights into the District and back up to Silver Spring and past White Oak. It’s also studying a line along the Capital Beltway loop, diverting the Blue Line from its current route across downtown to create a midcity rail line, or running an offshoot from the Green Line to National Harbor.

None of the plans is funded or even firm. Engineering hasn’t been done and land hasn’t been set aside. But the transit agency is studying what it will need by 2040 to accommodate growth in the region and relieve pressure on the system.