Exposure to risk on the roads

The concept of "exposure" to risk is used in the context that number of crashes is the product of exposure to risk and the rate of crashes per unit of exposure. In a practical sense, exposure refers to quantities such as distance travelled, time spent travelling, or number of vehicles passing a point. Comparison of crash rates of different groups of people, different types of vehicle, different roads, different environmental conditions, and so on, may be desired. This paper will examine vehicle registration data, counts of vehicles, surveys of vehicle use, and what is termed induced exposure that attempts to infer risk by distinguishing between crashes in which a party is "innocent" or "responsible". The concept of exposure has not yet achieved all that has been wished for in road safety research, because of problems with both the concept and its practical measurement. However, new technology offers considerable potential.