This
report uses two datasets on freight ton-miles. For one source, the Bureau of
Transportation Statistics (BTS) compiled the data from a variety of modal and
other sources to produce annual trend data. 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.
The
other set of freight ton-miles data 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.
