The quantifying of road safety developments.

The evaluation of the effectiveness of road safety policies and measures must be based on quantitative information on road safety developments and the relevant variables that influence that development. However, the concept of road safety itself is not well defined theoretically and quantitatively. Firstly, it concerns a multitude of related observable variables. Therefore, it is necessary that the relations between primary safety variables themselves, such as fatalities, serious and slight injuries and damage-only accidents, as well as their relation to exposure related variables (relevant for risk measurements), such as kilometrage, number of motor vehicles or optimally the frequency of encounters or conflict possibilities, are investigated in order to clarify the concept and its quantification. Secondly, road safety related variables are intrinsically unreliable due to random errors which may hide the true developments. The seldom used possibilities for error minimisation in the quantification of road safety are discussed as part of the quantified concept. Thirdly, the relevant variables are incompletely recorded due to selective and varying under reporting which distorts and underestimates the real developments. Lastly the implications of the matters for a targeted road safety policy, its monitoring and evaluation are highlighted. (A