The Intermodal Surface Transportation Efficiency Act of 19911 charged the Bureau of Transportation Statistics (BTS) with compiling, analyzing, and publishing a comprehensive set of transportation statistics, including information on:
- productivity in various parts of the transportation sector;
- traffic flows;
- travel times;
- vehicle weights;
- variables influencing traveling behavior, including choice of transportation mode;
- travel costs of intracity commuting and intercity trips;
- availability of mass transit and the number of passengers served by each mass transit authority;
- frequency of vehicle and transportation facility repairs and other interruptions of transportation service;
- collateral damage to the human and natural environment;
- the condition of the transportation system; and
- transportation-related variables that influence global competitiveness.2
For this report (as in the previous October 2003 Transportation Statistics Annual Report), BTS added three topics: transportation and economic growth, government transportation finance, and transportation energy. Each of these 15 topics is represented by a series of key indicators. Data tables supporting all the indicators are in appendix B at the end of the report. Appendix table numbers correspond to the figure numbers in this chapter.
About the Data in the Report
For consistency, most trend indicator data are shown over 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 10-year span for each indicator without sacrificing timeliness. Instead, the data span a decade up to the year of 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.
With a few exceptions, trend data involving costs have been converted to 2000 chained (“real”) dollars to eliminate the effect of inflation over time. Appendix B provides both 2000 chained dollar and current dollar value tables. Throughout the text in the report, results of most percent calculations have been rounded up or down, as appropriate, to a whole number. If the percent value is less than 5, data are presented with one decimal point, because rounding these data can mask differences when making comparisons. Average annual percentage change calculations have been made using a logarithmic formula to account for compounding over time.3 It is not always possible to obtain the same percentage or other calculation presented in this report using the tabulated data in appendix B. These differences occur because of the rounding of data on the printed tables.
Data in this report come from a variety of sources, principally from 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. Sampling data are subject to sampling variability. Documents cited as sources in this report often provide detailed information about definitions, methodologies, and statistical reliability.
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). Use of website data can be problematic. These data may be available one day and then revised or updated or removed shortly thereafter. Thus, the day and month of the BTS download from a website is included in the source information, along with the website address (url) at that time.
1 See 49 U.S. Code 111(c)(1).
2 This last item was added to 111(c)(1) by the Transportation Equity Act for the 21st Century in 1998.
3 The formula is: average annual rate = Exp [(lnY–lnX)/(n– m)] –1, where Y is the end year value, X is the initial year value, n is the end year, and m is the initial year.