NOTE: Container-trailer breakdown not available prior to 1988.
SOURCE: U.S. Department of Transportation, Research and Innovative Technology Administration, Bureau of Transportation Statistics, based on data from Association of American Railroads, 2004: Class I Rail Road Statistics, page 2; 1990-2003 Rail Road Facts 2003, page 26; 1980-1985 Rail Road Facts 1991, page 26; 1986-1989 Rail Road Facts 2001, page 26.