This paper is based on a study commissioned by the Finnish National Road Administration (see IRRD 813225). The purpose was to study the safety of main road junctions with the help of accident prediction models. The districts of the Finnish National Road Administration undertook an inventory of at-level junctions of major roads in the summer of 1988. The inventory was performed in 2700 junctions, of which 1762 were included in the modelling phase. The variation of the number of accidents was explained with traffic volumes and the variables collected in the junction inventory. The work was based on the theory of generalised linear models. The actual number of accidents was assumed to vary around the expected values according to Poisson or negative binomial distributions. The most important variables were those describing the magnitude and distribution of motor vehicle volumes. The number of accidents and their victims were generally found to be proportional to the total number of vehicles passing through the junction. The risk of accidents seems to increase as the traffic portion of the minor road increases. Several variables describing the road environment were also in the models. Accident models explained usually more than 80% of the systematic variation of the accident numbers. The systematic variation accounts generally for ca. 30% of the total variation of the accidents.
Samenvatting