The target of the presentation is to introduce the work achieved by Gruau together with Valeo, Inrets, Ratp and Veolia to add to the traction motor standard euro3 of a microbus a « stop & start » system developed by Valeo. Supercaps have also been installed to recover and save energy during braking phases. A vehicle has been especially built and dedicated to the project . Tests have been performed during a few months in the cities of Paris (Ratp) and Bourges (Veolia) to measure reduction of fuel consumption. In parallel to these practical experiments, simulations have been carried out by the Inrets laboratory. This work has demonstrated feasibility and interest of such a concept on urban buses which come to standstill three times per kilometer on an average.