The George Washington Memorial Parkway, colloquially the G.W. Parkway, is a 25-mile-long (40 km) limited-access parkway that runs along the south bank of the Potomac River from Mount Vernon, northwest to McLean, Virginia, United States, and is maintained by the National Park Service (NPS). It is located almost entirely in Northern Virginia, except for a short portion of the parkway northwest of the Arlington Memorial Bridge that passes over Columbia Island in Washington, D.C. The parkway is separated into two sections joined by Washington Street (State Route 400) in Alexandria. A third section, which is the Clara Barton Parkway, runs on the opposite side of the Potomac River in the District of Columbia and suburban Montgomery County, Maryland. A fourth section was originally proposed for Fort Washington, Maryland, but never built. The parkway has been designated an All-American Road. Virginia's official state designation for the parkway is State Route 90005.