Construction began on Interstate 495, the Capital Beltway, in 1956. By 1964, the 64-mile highway through Virginia and Maryland had encircled Washington, D.C.
It was the first major interstate route to be completed fully, and it opened April 2, 1964. By 1977, the beltway had been widened from four to eight lanes.
The interstate now carries up to 240,000 vehicles a day, and that total is expected to grow rapidly. The concept of expanding it to a 12-lane highway has been approved, and a working relationship has been established with a potential private sector builder.
Reconstruction of the Woodrow Wilson Bridge, which carries I-95 and I-495 traffic across the Potomac River, is currently the largest highway construction project in the United States.
The original span was opened in 1961. Designed for 75,000 vehicles per day, it now carries 195,000.
The Virginia, Maryland and U.S. transportation agencies are cooperating to build new bridges. They will have 12 lanes, twice the number on the current structure, and larger interchanges.
The project will cost about $2.5 billion. Construction began in March 2003, and will be complete in 2011.