Reducing the weight of vehicles could be a strong means of reducing fuel consumption in urban traffic. Published accident and injury statistics however show an inverse correlation of vehicle mass against injury severity in car to car collisions, above all in head-on collisions. This inverse correlation is in part caused by current crash test standards, where compatibility in collisions between cars of different size and weight is not a requirement. Compatibility in frontal collisions demands for significantly different deceleration-time curves in rigid barrier impacts for cars with different weight. Low mass vehicles (LMV) must meet compatibility criteria to comply with current injury criteria in real car to car collisions. Cars designed according to compatibility criteria can change future accident and injury statistics in a way that injury severity in LMVs can be reduced significantly.This study shows, that head-on collisions at closing speeds of up to 100 km/h with a mass ratio of 1:2 of the collision opponents can be survived with occupant loads well below the limits of actual injury criteria (FMVSS 208), if compatibility requirements are met with regard to car structure as well as restraint systems.