Diesel - electric traction is a well established technology in railways systems, mainly for lines with a low traffic potential. In those conditions, the choice of a diesel powered locomotive is due to the reduced costs compared to the infrastructure cost of a standard electric train. The main inconvenience of that technology is the primary energy source: oil resources are not infinite, prices are difficult to forecast and CO2 production increases global warming. It’s therefore important to develop new strategies to increase the energy efficiency of a diesel – electric train. To reach that goal, a system with supercapacitive energy storage will be proposed in this paper. The production and exploitation costs of the proposed system will be studied in more detail. The proposed solution will reduce diesel consumption and therefore also CO2 and other pollutant emissions while being economically viable.