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.