State Route 400 (SR 400) is a primary state highway in the U.S. state of Virginia. Locally known as Washington Street, the state highway runs from the south city limit of the independent city of Alexandria north to 1st Street, still within Alexandria. SR 400 is a city street connection through Old Town Alexandria between the two segments of George Washington Memorial Parkway, one heading south toward Mount Vernon and one heading north toward Washington. The Virginia Department of Transportation assigned the unsigned SR 90005 designation to the two segments of the parkway and SR 400.