BTS obtained the data in this report from many sources, including federal government agencies, private industries, and associations. Some of the data are based on samples and are subject to sampling variability. Data from all sources may be subject to omissions and errors in reporting, recording, and processing. Documents cited as sources for the tables often provide detailed information about definitions, methodologies, and statistical reliability.
Federal data are subject to guidelines, policies, and information practices that pertain to all federal agencies disseminating information to the public under Office of Management Budget directives (OMB).
Because federal agencies are subject to these guidelines, BTS relies on federal sources for the data used in this report where possible. A large number of federal agencies, both within the Department of Transportation and in other agencies, collect, compile, analyze, and publish transportation data. A partial list of these organizations is included in Table 1. In some cases, these agencies compile and disseminate data submitted or reported by states or private parties on transportation operations, planning, financing, or management. Some agencies also conduct surveys or otherwise directly collect data on particular matters, either through their own auspices or through partnerships with other entities. Still other agencies produce data or information relevant to transportation, even though transportation is not the primary purpose.
OMB chairs an interagency statistical policy committee, comprised of the heads of thirteen statistical agencies in the federal government, including RITA’s BTS. Statistical policies and guidelines for best practices are developed by this group and distributed to these and other agencies engaged in statistics.
RITA’s BTS has developed guidelines for good statistical practices in the transportation field in response to its legislative mandate. Specific topics covered include planning data systems, collection of 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 RITA’s BTS publications. Box A discusses various federal statistical quality manual and guidelines pertinent to transportation data.
Agencies also often have their own specific requirements and guidelines that may be 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. Source and accuracy statements in many cases are published by the source agency. The RITA’s 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.