Solomon, Brian (15 June 2016). "EMD DDA40X". The field guide to trains : locomotives and rolling stock. Minneapolis, Minnesota. hlm. 189. ISBN9780760349977. OCLC928614280.
Lemp, Hermann. U.S. Patent No. 1,154,785, filed April 8, 1914, and issued September 28, 1915. Accessed via Google Patent Search at: US Patent #1,154,785 on February 8, 2007.
Edison, Thomas A. U.S. Patent No. 493,425, filed January 19, 1891, and issued March 14, 1891 Accessed via the Edison Papers at: US Patent #493,425 on February 8, 2007.
Solomon, Brian (15 June 2016). "EMD DDA40X". The field guide to trains : locomotives and rolling stock. Minneapolis, Minnesota. hlm. 189. ISBN9780760349977. OCLC928614280.