From Virginia:

Richmond and Points South:

I-95 North to I-395 North. Take exit 10 (GW Parkway South); Take Airport Exit

Manassas and Points West:

I-66 East; Route 110 South to Route 1 South; Take Airport Exit

From Maryland:

Baltimore and Prince George's County:

I-95 South over Woodrow Wilson Bridge; Route 1 North; Take Airport Exit

Frederick & Montgomery Counties:

I-270South/
Washington, DC to I-495 South/
Northern Virginia; GW Parkway South; Take Airport Exit

From Washington, DC:

I-395 South; GW Parkway South; Take Airport Exit

For exact door-to-door directions, go to maps.yahoo.com and enter "DCA" in either the Destination or Starting Address boxes. Or choose "Find an Airport" on mapquest