DC Transit Authority

The DCTA was the company that owned and managed all of the D.C. Metro system before the Great War. The remnants of the D.C. Transport Authority can be seen around the Metro (the stations, rails, cars), and the acronym DCTA can be seen on the terminals that operate the Ticket Bot Protectrons. Also, the downloadable Metro map for your Pip-Boy is also called the DCTA Map.

The company must have been powerful before the war because of how big and well-promoted the Metro system was. All that was reduced to rubble when the bombs fell, and by 2277, the stations and tunnels were overrun by Raiders, Super Mutants, Feral Ghouls and other unpleasant "surprises".

Trivia
There is a DCTA in real life, the Denton County Transport Authority, but it's located in Denton County, Texas, far away from D.C.