This paper deals with the development of indicators used in controlling the safety performance of a transportation system. Because of the very large and complex nature of transportation systems, effecting any changes proceeds very slowly. In addition, changes in the control variables by countermeasures generally have an output response that can only be observed after a rather long period (slowness of accident registration). Decision makers need indicators that detect changes at an early stage in order to anticipate developments in the output of the transportation system. In order to control the safety of the system, they need knowledge about the relation between the changes brought about by possible countermeasures and the effects thereof. However, causal relations between countermeasures and output indicators are too complicated. What is needed is a breakdown of the total process into subprocesses and a theory explaining the effects of attributes of countermeasures on each of these subprocesses. This paper discusses a structure of subprocesses that facilitates the development of process-indicators that can be linked up with the theories relevant for the subprocesses. These process-indicators and the relevant theories should have sufficient predicting force for the effect of countermeasures. (A)
Abstract