Vehicle Safety is very attractive, concerning active or passive safety. The collisions are intensively studied including deformations, kinematics, protections, devices and injuries. By the way, today we have a lot of computer programs trying to simulate these crash-tests. But, we can have an idea about the magnitude of the impact forces of a vehicle against a rigid wall starting from known physical concepts and simplified approximations. This is one of the purposes of this work.The classic problem of projectile impacts against a rigid wall and the example of an aircraft impact against a nuclear power plant are used to consider the models applied to vehicles.We consider the disacceleration of a material point and also the vehicle as an extense object.Real data are used to quantify the achieved expressions. We compare and discuss the magnitude of the forces, for instance, between a passenger car and a commercial vehicle. We use the results to discuss the qualification of seat anchorage, some parameters concerning deformation and aspects of frontal impacts regarding passenger cars and commercial vehicles.