One configuration of a hybrid electric vehicle is the split-axle parallel architecture, which enables existing ICE-powered vehicles to be retrofitted into a hybrid electric vehicle (HEV) with minimal modification achieved by placing electric motors in the hub of the non-driven wheels. This paper describes benefits of a hybrid drive-train and presents development work of an experimental prototype of the retrofit hybrid system, implemented on a Proton WAJA. It explains operation of the retrofit vehicle's energy management system and describes a dynamic simulation model for the HEV. Preliminary simulation studies show a fuel reduction of 25 compared to the ICE only-powered vehicle. Economic consideration requires further improvement of the fuel reduction, for the system to be commercially viable. This paper suggests for further research, an improvement to the simple retrofit system and investigation of various energy management strategies, to improve the fuel economy. Finally, this work describes experimental set-up for field testing and hardware-in-the-loop (HIL) simulation of the retrofit HEV. © 2011 IEEE.