The Intermodal Surface Transportation Efficiency Act of 19911 and subsequent authorizing legislation charged the Bureau of Transportation Statistics (BTS)-now a part of the Research and Innovative Technology Administration-with compiling, analyzing, and publishing a comprehensive set of transportation statistics, including information on a specified list of topics.

In this chapter, each of these 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 the chapter. The chapter is organized thematically rather than in the order the topics are presented in the legislation (table 1). As in the two previous annual reports, BTS includes three topics that are not on the congressional list.

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 were 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. Annual growth rate calculations are made using a logarithmic formula to account for compounding over time.2 A reader may not obtain the same percentage or other calculation presented in this report using the tabulated data in appendix B because of the rounding of data on the tables.

Data in this report come from a variety of sources, principally from BTS and 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). 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.

1 See 49 U.S. Code 111(c)(1). As this report was nearing completion in 2005, the U.S. Congress enacted the Safe, Accountable, Flexible, Efficient Transportation Equity Act-A Legacy for Users (SAFETEA-LU, Public Law 109-59). This legislation amended section 111(c)(1). These amendments are discussed in this report's chapter 3, The State of Transportation Statistics.

2 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.