The Indian railways have undertaken an ambitious plan of electrifying the entire railway network in the country. In the interim, mixed routes of traction are inevitable and will continue to exist. Electric locomotives can work only with overhead catenary supply, whereas diesel locomotives have the flexibility to operate anywhere on the Indian railways network.

Dual-mode (diesel + electric) locomotives can work with diesel engine as the primary power source while operating in non-electrified routes and work as an electric locomotive by drawing power from overhead catenaries in electrified sections.

The RDSO has drawn up plans to convert the EMD WDP4D locomotives to dual fuel mode that will run on both diesel as well as AC electric traction. And unlike the converted WAGC3, the WDAP4 (now WDAP 5) will be a true dual-mode locomotive. The proposed WDAP5 locomotive is being designed to haul 26 air conditioned cars at a top speed of 135 Kmph.