"From 1912-61 tunnels below the U.S. Senate building were filled with monorail cars carrying senators on the "shortest and most exclusive railway in the world." A short history about the monorail system appears on the Senate.gov website and is excerpted below.
I'm fascinated with early ideas of what "the monorail" was to become and even more fascinated with the transportation systems that (as in this case) were actually tried."
FROM SENATE.GOV:"The distance between the old Senate Office Building and the Capitol was only a fifth of a mile, but senators needed to traverse it multiple times on a typical legislative day. Had the Capitol been a skyscraper, elevators would have whisked members from their offices on different floors to the chamber. Instead, the office building and Capitol were linked by a horizontal elevator: a subway. Initially, transportation in the subway tunnel was provided by battery-powered yellow Studebaker coaches. Ten passengers could ride in each car, facing each other on benches. The buses ran along a concrete roadway at a maximum speed of 12 miles an hour. Rather than turn around at each terminus, they backed up for the return trip."