Transportation Research Thesaurus (TRT)

Items of Interest

The Transportation Research Thesaurus is a hierarchical, faceted collection of concepts that logically arranges in accordance with their relationships to one another. This taxonomical approach puts like intellectual content together. By selecting the most appropriate concept in the intellectual order the work is identified with related works. The TRT is used by indexers, content managers and librarians in the transportation community and is an internationally recognized standard.


The Transportation Research Thesaurus (TRT) covers all subjects related to the following transportation modes:

  • Air
  • Land
  • Water
  • Space
  • Ground (more in-depth coverage)

It also includes formal names of organizations, persons, computer programs, places, etc, however, these concepts are no longer being updated


Each term in the TRT is assigned a unique notational code that conveys its location within the hierarchy. The first letter of the notation represents the facet or top term. Using the notational code it is easy to determine the terms relation in the hierarchy. The term's parent (Ae) will have one less letter (from the right end) as the term (Aea). Siblings (Aeg, Aes) will have the same notational code as the term except the last letter will be different. Children (Aeac, Aeah) will have one letter appended to the end of the notational code of the term.

Tree graphical image showing TRT relationships

Figure 1: Example of the TRT Structure

The full display shows relationship of terms including SN (Scope Notes), UF (used for terms), BT (Broader Term), NT (Narrower Term), RT (Related Term), NN (Notational Code), and CT (Cross Reference Term).


The National Transportation Library assumed responsibility for the TRT for the transportation information community in October 2007. Before that time, NTL was an active user and supporter. In its new role as manager of the TRT, NTL has established new procedures for change and review.


The Transportation Research Thesaurus (TRT) was developed under NCHRP Project 20-32 to provide a tool to improve the indexing and retrieval of transportation information. The thesaurus covers all modes and aspects of transportation. These terms are used in the indexing of the Transportation Research Board's database the Transportation Research Information Services (TRIS) and its web accessible version TRIS Online by the National Transportation Library, as well as other transportation libraries.

The TRT was designed and developed by CDB Enterprises, Inc., of Silver Spring, MD, under contract to the National Cooperative Highway Research Program, administered by the Transportation Research Board, National Research Council, with sponsorship by the American Association of State Highway and Transportation Officials, in cooperation with the Federal Highway Administration, U.S. Department of Transportation. Originally, the Transportation Research Board maintained the Transportation Research Thesaurus. Online access to the Transportation Research Thesaurus was hosted by the National Transportation Library under a cooperative agreement between the Bureau of Transportation Statistics and Transportation Research Board. In October 2007, the National Transportation Library has assumed content and access responsibility with technical assistance from the TRB Library and Information Science in Transportation Committee TRT Subcommittee.

For further information on the development of Transportation Research Thesaurus see NCHRP Report 450 - Transportation Research Thesaurus and User Guide available through the TRB Electronic Bookstore (link