Describing the evolution in the number of highway deaths by a decomposition in exposure, accident risk and fatal risk

Abstract

The general purpose of this research is to improve the insight in road safety on Belgian highways by means of a layered model. In this study, the monthly number of persons killed on highways in Belgium will be decomposed in three parts, namely exposure, accident risk and fatal risk. The evolution in these three dimensions will be investigated separately. More specifically, for each dimension a descriptive and explanatory analysis will reveal the most optimal unobserved components model. The separate analysis of each dimension may reveal different underlying developments. We will study the impact of meteorological, socioeconomic, legislative and calendar factors on exposure, accident risk and fatal risk. The analysis shows that, although for each dimension the same basic components are available, the optimal model of each dimension has its unique structure of descriptive components and significant variables. Precipitation and snow enhance accident risk while temperature plays a significant role for exposure. Fatal highway risk decreases in case of an extra day with precipitation and was significantly affected by the child restraint law. The economic indicators mainly affected accident risk. Bringing the three models back together shows that the number of highway deaths during 1993-2001 has well been reconstructed.