National Transportation Statistics
This organization, part of the Department of Transportation, generates a variety of statistics on the U.S.'s transportation system. Besides "Transportation Statistics Annual Report" (found in the "Transportation Studies" section), this site includes other extensive data (in spreadsheet format) from the "National Transportation Data Archive." This includes the "FAA Statistical Handbook of Aviation" and the "Commodity Flow Survey," a joint project of the DOT and Census which tracks shipments in the U.S. There are also data sets from the FAA, the Coast Guard, the Federal Highway Administration, and the Army Corps of Engineers. It also contains information on the "Journal of Transportation and Statistics," sponsored jointly by the Bureau of Transportation Statistics and the U.S. Department of Transportation.