In the recent years, a new interest on kinetic energy recovery (KER) of vehicles arose. In USA, car manufacturers (Ford, Sheep et al.) developed research programs on the use of hydraulic devices to realize KER system, also with economical support of government body (EPA). In 2002 Ford built a very interesting prototype (Ford Tonka) using such recovery device (named HLA, Hydraulic Launch Assist), achieving very interesting improvements of fuel economy and pollution, besides increasing of acceleration and making feasible downsizing of thermal engine. Nowadays, also D.I.M.E.G. of University of L'Aquila (Italy) is working about HLA systems and, in order to study its behaviour, a simulation model (named V&HLA-SC) particularly useful to evaluate its energetic efficiency and performance has developed. The studies here reported show that the system efficiency may be modified by different ways of driving a mission that is characterized by different braking and acceleration time, mantaining constant elapsed time and covered distance. In such a way, optimal driving strategies and/or control system laws may be suggested to optimize the cyclic process of recovering and reusing kinetic energy, i.e. to achieve the optimal use of HLA system, especially in urban areas.