Book excerpt: A transportation indicator is a measure of change over time in the transportation system or in its social, economic, environmental, or other effects. Two National Research Council (NRC) studies recommended, as a matter of high priority, that the Bureau of Transportation Statistics (BTS) in the U.S. Department of Transportation (USDOT) develop a consistent, easily understood, and useful set of key indicators of the transportation system. The NRC's Committee on National Statistics and its Transportation Research Board, which conducted these studies, convened a workshop on June 13, 2000. The purpose of the Workshop on Transportation Indicators was to discuss issues relating to transportation indicators and provide the Bureau of Transportation Statistics with new ideas for issues to address.