495sucks.com: Promotes change to improve rush-hour traveling conditions on I-495 and other area highways.
DCRoads.net: Guide to the expressway, parkway, bridge and tunnel network in the Washington-Baltimore metropolitan area. Exit listings for area highways.
District Department of Transportation: Official site includes planning and construction information.
District of Columbia Highway(s): Information about the one district-numbered highway (Route 295) and others that could be.
Roads to the Future: Includes in-depth articles about many features.