Dimensions of road safety problems and their measurement.

This paper identifies nine characteristics of road safety problems that are all in principle amenable to numerical measurement. The nine characteristics identified are: 1. Magnitude 2. Severity 3. Externality 4. Inequity 5. Complexity 6. Spatial dispersion 7. Temporal stability 8. Perceived urgency 9. Amenability to treatment. The purpose of identifying these dimensions and of trying to measure them is to provide a basis for selecting problems for treatment by means of safety programmes. Selecting problems for treatment usually cannot be done on the basis of a single dimension, as it is the mix of characteristics that determine the prospects for successfully treating a problem. It is proposed that amenability to treatment is a function of complexity, perceived urgency and the availability of cost-effective treatments. Speed and speeding is used as an example of a road safety problem to illustrate how the various dimensions can be measured.