BTS obtained the data in this report from many sources, including other federal agencies, private industry, and trade associations. Data based on surveys are subject to sampling variability. Data from all sources may be subject to omissions and errors in reporting, recording, and processing. The sources cited for each table often provide additional information about the definitions, methodologies, and statistical reliability.
Under Office of Management Budget (OMB) directives, data collected by federal agencies are subject to guidelines, policies, and practices for disseminating statistics to the public.
Because federal agencies are subject to these guidelines, BTS relies heavily on federal sources for the data contained within this report. Federal agencies, both within and outside of the U.S. Department of Transportation (U.S. DOT), collect, compile, analyze, and publish transportation data. A partial list of these organizations is included in box A. In some cases, these agencies compile and disseminate data submitted or reported by state and local governments and/or by private industry on transportation operations, planning, financing, or management. Furthermore, some federal agencies conduct surveys or otherwise directly collect data on specific matters, either through their own auspices or through partnerships with other entities. In addition, other agencies produce data or information relevant to transportation, even though transportation is not their primary focus.
OMB chairs an interagency statistical policy committee, comprised of the heads of 13 statistical agencies in the federal government, including BTS. This group develops and distributes these statistical policies and guidelines for best practices to these and other agencies involved in statistics.
In response to its legislative mandates, BTS has developed guidelines for good statistical practices in the transportation field. Specific topics covered include planning data systems, collecting data, processing data, dissemination of information, and evaluation of information quality. These guidelines apply to all information, including compilations containing data from other sources, appearing in BTS publications. Box B discusses various federal statistical quality manuals and guidelines pertinent to transportation data.
Agencies also often have their own specific requirements and guidelines in addition to government-wide guidance. For example, they may issue guidelines for data reporting by state agencies, localities, and transportation providers. Such guidance may contribute to greater uniformity, comparability, and quality of the resulting data even though it comes from multiple providers.
In many, but by no means all cases, source agencies document the methods used in collecting, compiling, and assuring the quality of the data they produce. In many cases, the cited agencies publish source and accuracy statements. The BTS website for National Transportation Statistics, a web-based companion document to this report, summarizes much of this information with respect to particular data series (National Transportation Statistics, Appendix E-Data Source and Accuracy Statements, http://www.bts.gov/publications/national_transportation_statistics/ ).
Box A: Selected Federal Agencies that Collect or Compile Transportation Data
Multimodal Data (including economic data)
Maritime and Inland Waterways Data
Other Agencies Collecting Data Related to Transportation
KEY: USDHSU.S. Department of Homeland Security; USDAU.S. Department of Agriculture; USDOCU.S. Department of Commerce; USDOEU.S. Department of Energy; USDOLU.S. Department of Labor; USDOTU.S. Department of Transportation
Box B: Information Quality Guidelines for Federal Transportation Data
As a federal statistical agency, the Bureau of Transportation Statistics (BTS) has its own statistical standards and participates with other agencies to improve statistical information quality. Under an array of guidelines, other federal agencies collect, compile, and disseminate statistical data. The following are key guidelines and statistical information quality documents:
On March 7, 2008, the Office of Management and Budget released Statistical Policy Directive No. 4: Release and Dissemination of Statistical Products Produced by Federal Statistical Agencies: (http://www.whitehouse.gov/omb/fedreg/2008/030708_directive-4.pdf).