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The U.S. Department of Transportation (USDOT) was established in 1966. Its mission is to "Serve the United States by ensuring a fast, safe, efficient, accessible and convenient transportation system that meets our vital national interests and enhances the quality of life of the American people, today and into the future." The U.S. Coast Guard was formerly part of USDOT but is now part of the Department of Homeland Security.
Government Documents has an extensive collection of Department of Transportation documents, including the following series:
Technical reports DOT- (various series) (TD 1.20/) Reports on transportation infrastructure and mass transportation.
Merchant vessels of the United States (TD 5.12/2:) "Lists the names of U.S. merchant and recreational vessels documented under the laws of the United States. It provides vessel dimensions, tonnage, build (if available), and ownership information." (Coast Guard web site)
Government Documents also has many general publications, handbooks, manuals, posters, CD-ROMs, and other material from USDOT, as well as Congressional hearings and documents about transportation.