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Highways: Includes all public road and street mileage in the 50 states and the Distric of Columbia. Approximately 43,000 miles of Bureau of Land Management Roads are excluded.
Transit: The figures have been added up and rounded. Beginning in 2011, Light rail includes Light Rail, Street Car Rail, and Hybrid Rail. Transit system length is measured in directional route-miles. Directional route-miles are the distance in each direction over which public transportation vehicles travel while in revenue service. Directional route-miles are computed with regard to direction of service, but without regard to the number of traffic lanes or rail tracks existing in the right-of-way. Beginning in 2002, directional route-mileage data for the Commuter and Light rail modes include purchased transportation. 2005 and later years directional route-mileage data for the Heavy rail mode include purchased transportation.
Navigable channels: The figures are estimated sums of all domestic waterways, including rivers, bays, channels, and the inner route of the Southeast Alaskan Islands, but do not include the Great Lakes or deep ocean traffic. The Waterborne Commerce Statistics Center considers 12,000 miles as commercially significant inland shallow-draft waterways as of 2007.