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Transportation Research Thesaurus

The Transportation Research Thesaurus is a hierarchical, faceted collection of concepts logically arranged 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. This thesaurus is used by indexers, content managers and librarians in the transportation community. It is a nationally recognized standard.

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 TRID, the TRIS and ITRD database, by the National Transportation Library, and by 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. The Transportation Research Board currently maintains the Transportation Research Thesaurus. Online access to the Transportation Research Thesaurus is hosted by the National Transportation Library under a cooperative agreement between the Bureau of Transportation Statistics and Transportation Research Board.

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


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

It does not cover formal names of organizations, persons, computer programs, places, etc.


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.


TRT is provided in cooperation with TRB and in support of activities to make the TRT more accessible to taxonomists and authors.  It reflects changes provided by TRB to the NTL on a bimonthly basis.

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