APA
U.S. Federal Highway Administration, . (1972). Highway Sign Symbology. International Conference. Washington, June 5-6, 1972. Proceedings. Washington DC: U.S. Federal Highway Administration.
Chicago
U.S. Federal Highway Administration, . 1972. Highway Sign Symbology. International Conference. Washington, June 5-6, 1972. Proceedings. Washington DC: U.S. Federal Highway Administration.
Harvard
U.S. Federal Highway Administration, . (1972). Highway Sign Symbology. International Conference. Washington, June 5-6, 1972. Proceedings. Washington DC: U.S. Federal Highway Administration.
MLA
U.S. Federal Highway Administration, . Highway Sign Symbology. International Conference. Washington, June 5-6, 1972. Proceedings. Washington DC: U.S. Federal Highway Administration. 1972.