So far in the Twenty-first century the field of people transportation has had numerous setbacks, of these some are related to air pollution and some to the rarefaction of petroleum sources. Studies have been undertaken within this domain for many years now. Hybrid vehicles in which the conventional energy source is kept and an on-board energy source is added are showing themselves to be a potentially good solution in the short term. In these hybrids the vehicle autonomy is assumed by the first energy source and the power constraints are taken upon by the second. Moreover, the storage element adds the possibility to recuperate the braking energy in an optimal way. During the last decade, an important development has come about in the field of energy storage elements. The supercapacitors newly appearing on the scene are power components well suited for an application in transportation domain: their lifetime is over 500,000 cycles and their power density (W/kg) is much higher than for batteries. The present work is concerned with air pollution and energy storage elements and presents the details of using a power assistance system for vehicles. In this case, the auxiliary power energy storage element is on board and is made of supercapacitors. The decreased energy consumption of the vehicle is directly dependant on the vehicle's type, the route driven and the size of the storage element within the vehicle. An optimal method of sizing the energy storage element is developed. An application of the principles is presented in three different categories of vehicle: a transportation network fed by catenaries, a diesel-electric vehicle and a light electrical vehicle. In all three cases, the size of the storage elements, the on-board energy control system and the reduction of the vehicle consumption are defined. Following the different methods developed here, it is possible to define the conditions for when a power assistance system can give a real decrease in the vehicle's energy consumption. When an on-board storage element is added in a vehicle, a static converter has to be used. Its main role is to adapt the voltage level between the storage element and the other vehicle propulsion equipment and to control the energy flow on board the vehicle. An interleaved mutichannel continuous-continuous converter operating in a discontinuous conduction mode is especially dedicated to mobile applications. This type of converter is lighter and smaller in volume, yet its efficiency is greater.