About Transportation Services Index

The Transportation Services Index (TSI), created by the U.S. Department of Transportation (DOT), Bureau of Transportation Statistics (BTS), measures the movement of freight and passengers. The index, which is seasonally adjusted, combines available data on freight traffic, as well as passenger travel, that have been weighted to yield a monthly measure of transportation services output.

For charts and discussion on the relationship of the TSI to the economy, see our Transportation as an Economic Indicator: Transportation Services Index page (https://data.bts.gov/stories/s/TET-indicator-1/9czv-tjte)

For release schedule see: https://www.bts.gov/newsroom/transportation-services-index-release-schedule

About seasonally-adjusted data

Statisticians use the process of seasonal-adjustment to uncover trends in data. Monthly data, for instance, are influenced by the number of days and the number of weekends in a month as well as by the timing of holidays and seasonal activity. These influences make it difficult to see underlying changes in the data. Statisticians use seasonal adjustment to control for these influences.

Controlling of seasonal influences allows measurement of real monthly changes; short and long term patterns of growth or decline; and turning points. Data for one month can be compared to data for any other month in the series and the data series can be ranked to find high and low points. Any observed differences are “real” differences; that is, they are differences brought about by changes in the data and not brought about by a change in the number of days or weekends in the month, the occurrence or non-occurrence of a holiday, or seasonal activity.

The National Transportation Library (NTL) provides national and international access to transportation information, coordinates information creation and dissemination, and provides reference services for Department of Transportation (DOT) employees and public stakeholders. Established in 1998 by the Transportation Equity Act for the 21st Century (TEA-21; P.L. 105-178), NTL’s authorized role was expanded in 2012’s Moving Ahead for Progress in the 21st Century (MAP-21; P.L. 112- 141). NTL’s primary product and service is the Repository and Open Science Access Portal (ROSA P) (https://rosap.ntl.bts.gov).

NTL’s collections in ROSA P are full-text digital publications, datasets, and other resources. Legacy print materials that have been digitized are collected if they have historic, technical, or national significance. The repository is also designated as the full-text repository for USDOT-funded research under the USDOT Public Access Plan. Collections in ROSA P are available without restriction to transportation researchers, statistical organizations, the media, and the general public.