Grava, S. (2003). Urban transportation systems. McGraw-Hill.
Lua i Stíl Chicago (17ú heag.)Grava, Sigurd. Urban Transportation Systems. McGraw-Hill, 2003.
Lua MLA (8ú heag.)Grava, Sigurd. Urban Transportation Systems. McGraw-Hill, 2003.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.