Most recently, the Bureau of Transportation Statistics (BTS) has gathered three datasets on freight ton-miles. Here, BTS compiled the data from a variety of modal and other sources to produce annual trend data (see table 1-9b in appendix B for source details). The coverage of the modal data is often incomplete, and the BTS process of developing these data attempts to provide a more comprehensive estimate of all domestic freight ton-miles. For instance, while ton-miles data are readily available for the large Class I railroads, BTS estimates ton-miles for smaller railroads to arrive at total freight rail ton-miles.
A second set of annual BTS ton-miles data has been produced for many years and published in National Transportation Statistics (NTS). These data provide estimates of freight ton-miles back to 1960 but are not as comprehensive as the estimates presented here. BTS is in the process of updating these NTS data using the methodology described above.
The third set of freight ton-miles data-discussed in the next pages-come from the Commodity Flow Survey (CFS) conducted every five years by BTS and the U.S. Census Bureau of the Department of Commerce. As a survey, the methodology and coverage of this dataset differ from the above and the data are not comparable. For instance, according to the CFS, total 2002 ton-miles are 3.1 trillion and with supplemental estimates added rise to 4.5 trillion ton-miles.