Risk is a measure for the threat of property and health of both directly and indirectly involved persons coming from a system. The risk is measured with the help of the expectation of loss. A residual risk always remains because failure and dangerous situations can never be prevented completely. A system is called safe when the expectation of loss of the system is not bigger than the maximum of authorized loss limitation. In traffic, for example, the risk is increasing in proportion to the speed of the means of transport. The force of the impact at different speeds can be explained by the corresponding drop height: 40 Km/h corresponds to a free height of fall of 6 metres 60 Km/h corresponds to a free height of fall of 14 metres 80 Km/h corresponds to a free height of fall of 25 metres