Regarding traction systems, new solutions can be proposed today, where energy storage with supercapacitors can offer an easier energy management, together with a strong decrease of the constraints applied to the main energy source of such systems. The energy density of supercapacitors is not so high that these components can be used as main energy sources. However, their power density allows those components to supply efficiently power peak demand of the vehicle, minimizing so power constraints on the main energy source: batteries, thermal engine, catenaries, etc… The aim of this contribution is to define typical applications fields for supercapacitors, in the general domain of traction systems. The supercapacitors will be first defined, and models will be proposed. A method for sizing supercapacitors will be described, taking into account energy and power requirements to match efficiency as high as possible. Two main applications will be then described and commented: supercapacitors as complementary power supply, associated with batteries in an electrical scooter application. It will be described how the sizing of a batteries tank can be optimized thanks to supercapacitors. The second application will present an application where supercapacitors are used as energy feeders for weak distribution networks (trolley-buses supply).