On the Senate side, two separate subway lines exist. 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 other is a computer-controlled system with three enclosed trains of three cars each running on a 90-second schedule, connecting the Hart Senate Office Building, the Dirksen Senate Office Building, and the Capitol. The train cars are unpowered; the train is propelled by a track-side linear motor. This line has two parallel tracks for most of its length, but at the Hart and Capitol stations the tracks converge into one, with a single side platform. This allows easy return travel on the opposite track. The Dirksen station features a side platform for Capitol-bound trains and an island platform for Hart-bound trains. All three of these stations feature platform screen doors. A small maintenance spur is located adjacent to the Hart station.
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.
Members of 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. During votes, the House subway is restricted to congressional members. The Russell subway is restricted to members and staff during Senate votes.
Since the terrorist attacks of September 11, 2001, restrictions have been placed on visitors using the Senate subway between the Hart and Dirksen buildings.
A collision occurred on October 2, 2007, in the Rayburn to Capitol subway line after a car failed to slow down when it reached the end of the track line. The operator was injured and taken to a hospital for observation.
Then Senator John W. Bricker was shot at by former Capitol Police officer William Louis Kaiser on July 12, 1947. Bricker survived as the shots did not hit him.