Relationships between Accidents and Geometric Characteristics for Four Lane Median Separated Roads

The effects of geometric characteristics on the accidents of the A3 Naples-Salerno, which is among the riskiest motorway in Campania (Italy), are reported in this paper. For the purpose, all the accidents which occurred during a twenty month period (August 1998 - March 2000) from Km 5+00 to Km 55+00 (for a section of 50.0 km) have been examined. All the information on the accidents were taken from the Road Police reports, while the horizontal and vertical alignments were obtained from the road plan. The study was carried out by the univariate analysis, therefore the accident data were elated to the following single variables: length of tangents, radii of circular curves, longitudinal grade, change in operating speeds between two consecutive geometric elements having constant curvature, and sight distance. Therefore relationships between these geometric parameters and the accidents which occurred on the motorway studied, that is a four-lanes median-separated road, have been developed. The accident data have also been related to the pavement surface conditions, so relationships to the Side Friction coefficient and macro-texture have been developed too