The vehicles, hybrids according to the importance of the electrical part and how it is combined with the engine. The nomenclature varies depending on sources and manufacturers, the most used is:

• The Micro Hybrid solution, corresponding to the lowest level of hybridization, is illustrated by Stop & Start system available on the Citroen C2 and C3. It is a reversible electric motor fulfilling the roles of starter and alternator on a conventional car, combined with the automatic shut the engine when the vehicle stops, thereby substantially reducing the consumption of urban route ( and only there).

• The Mild Hybrid are an intermediate level of hybridization. The Urban Hybrid system called PSA (concept car-C5 Airscape) is a stop & start the extended functionality that can also provide regenerative braking (the electric motor operates as a generator and provides additional engine braking torque) and provide an extra power to help occasions, the energy is stored in the meantime in batteries or super capacitors. Comparable technologies exist at BMW, Honda (Honda Insight) or Ford.