Alaska Transportation Research & Technology Transfer Center (select Research & Tech category within the Alaska DOT site dropdown menu)

American Public Transportation Association - APTANet Information Center  
    - Search the APTA catalog

Arizona Transportation Research Center Library

Center for Transportation Research Library, University of Texas at Austin

Directory of State Highway and Transportation Department Libraries

Elsevier TransportConnect

Kentucky Transportation Center

Los Angeles Metropolitan Transportation Authority

LTAP Clearinghouse

MTC-ABAG Library (Metropolitan Transportation Commission - Association for Bay Area Governments)

Minnesota Transportation Libraries

Montana State Library

National Transportation Library

Northwestern University Transportation Library

Ohio State Library/Ohio Dept. of Transportation Library

Québec Ministère des Transports. Centre de documentation

Ernest H. Robl Stock Photography Library

South Dakota Deparment of Transportation Library Catalog
     - SDDOT Research Office downloadable reports

Transportation Research Board Library

Texas Transprtation Institute
     - TTI Publications Catalog

Transportation Resource Exchange Center

UMTRI Library

United States Department of Transportation:
    Library
    Library Services to the Public
    Online Digital Special Collections

University of California at Berkeley Institute of Transportation Studies - Harmer E. Davis Transportation Library
    TransLiblog

Washington State Department of Transportation Library

Wisconsin Department of Transportation Library