BOX 1
About the Data in this Report
The
data in this report come from a variety of sources, principally from the Bureau
of Transportation Statistics (BTS) and other operating administrations of the
U.S. Department of Transportation. However, other sources are federal
government agencies, such as the U.S. Census Bureau, the Bureau of Economic
Analysis, the U.S. Environmental Protection Agency, the U.S. Coast Guard, and
the Energy Information Administration. To supplement government sources, the
report occasionally uses data and information from trade associations, such as
the Association of American Railroads and the American Public Transportation
Association. Data from any of these sources may be subject to omissions and
errors in reporting, recording, and processing. Sample data are subject to
sampling variability. Documents cited as sources in this report often provide
detailed information about definitions, methodologies, and statistical
reliability.
To
be consistent, when trend data are used in this report they are shown, if
possible, for at least a 10-year period. Because of the differing availability
of data among all the indicators included, it has not been possible to use the
same span of 10 years for each indicator without sacrificing timeliness. Instead,
the data span a decade up to the year of the most recent data available when
this report was prepared. There are some instances where less than 10 years of
data are presented—either because the data are not comparable over the period
or are not available.
Source
information in the report details where BTS obtained data used (e.g., from a
printed document, website, or by direct communication with an individual). The
same data BTS obtained from websites and used in this report may not be
available to readers because of frequent changes in such postings. However, the
day and month of the BTS download is included in the source information, along
with the website address (url)
at that time.
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