[Exposure to the risk of traffic accidents, a fundamental epidemiological parameter, and one difficult to measure]

This is a review of the literature dealing with exposure to the risk of traffic accidents. We present the principal definitions of this concept, the different measures of risk exposure, indicators of the risk of traffic accidents, and the advantages and disadvantages of the methods used for the collection of data. The validity of the measure of exposure to risk is analyzed as well. We conclude that while distance travelled is the principal measure of exposure to risk accepted by the research community, it is necessary to use a composite measure which also takes into account the risk associated with the driver.