Cita APA

Libby, H. W., & Libby, H. W. (1949). Standard highway spiral. Oregon: Oregon State Highway Commission.

Citación estilo Chicago

Libby, H. W., y H. W. Libby. Standard Highway Spiral. Oregon: Oregon State Highway Commission, 1949.

Cita MLA

Libby, H. W., y H. W. Libby. Standard Highway Spiral. Oregon: Oregon State Highway Commission, 1949.