The original subway line was built in 1909 to link the Russell Senate Office Building to the Capitol.

[2] A two-car subway line connecting the Rayburn House Office Building to the Capitol was built in 1965.

The first is a crewed two-track system, with a single open-topped car operating on each track, connecting the Russell Senate Office Building and the Capitol.

The House and Senate subway systems do not terminate in the same location under the Capitol, but they are connected by a labyrinth of tunnels.

The public can travel on the trains — usually during a tour of the Capitol Complex — but must be escorted by a staff member with proper identification.