[Washington, District of Columbia] : U.S. Department of Transportation, Research and Innovative Technology Administration, Bureau of Transportation Statistics, 2009
[Washington, District of Columbia] : U.S. Department of Transportation, Research and Innovative Technology Administration, Bureau of Transportation Statistics, 2009
[Washington, District of Columbia] : U.S. Department of Transportation, Research and Innovative Technology Administration, Bureau of Transportation Statistics, 2009
[Washington, District of Columbia] : U.S. Department of Transportation, Research and Innovative Technology Administration, Bureau of Transportation Statistics, 2008
[Washington, District of Columbia] : U.S. Department of Transportation, Research and Innovative Technology Administration, Bureau of Transportation Statistics, 2008