Road accidents and traffic flows: An econometric investigation

This paper develops an empirical model of the relationship between road tra ffic accidents and traffic flows. The analysis focuses on the accident exte rnality, which is determined mainly by the difference between the marginal and average risks. The model is estimated using a new data-set which combin es hourly London traffic count data from automated vehicle recorders togeth er with police records of road accidents. The accident-flow relationship is seen to vary considerably between different road classes and geographical areas. More importantly, even having controlled for these and other differe nces, the accident externality is shown to vary significantly with traffic flows. In particular, while the accident externality is typically close to zero for low to moderate traffic flows, it increases substantially at high traffic flows.