Accident rates and accident cost rates are calculated for different road types and junction types by using existing data for Swiss federal roads and by evaluating new accidents.
The accidents at segments without junction are selected according to their connection to the road axis and then they are evaluated by using the length of the segment. At junctions accidents are selected according to a polygon that surrounds the junction and the accidents.
A model for the accident rate and the accident cost rate needs to be developed from the results of the accident evaluation. The model will allow estimations of the rates depending on multiple attributes.
The objective of the project i to develop a model for accident (cost) rates can estimate or give a prognosis the rates for different road types and junction types.
The result of the research is a calculation of accident rates and figures as well as accident cost rates and figures for different types of road sections and intersection categories. Based on the accident cost rates and figures the expected monetary effects of road design options on the accident situation can be calculated and these rates and figures can be used in cost-benefit analysis to cover the influence of traffic safety. Parts of the research results are published in the standard SN 641 824 "KostenNutzen-Analysen im Strassenverkehr, Unfallraten und Unfallkostensätze".
To adequately cover the effects of accidents in cost-benefit analysis, it is essential for this analysis to be based on the real accident situation, which in quantitative terms differs considerably from the accidents reported by the police. The unreported accidents are included in this study by the use of correction factors. The rates and figures that were calculated for the standard contain not only the reported accidents but also partly include correction factors for the unreported accidents. Therefore the rates and figures cannot be used as reference values in local accident analysis. This must as well be taken into account when compared of with rates and figures reported in the literature.
Furthermore the calculation of accident rates and figures and accident cost rates figures on primary and secondary roads distinguishes between road sections and intersections. This is an additional reason why the figures and rates are not comparable to values taken from the literature or NISTRA.
The study establishes accident rates and accident cost rates for the following road types: motorway with two lanes, motorway with three lanes, expressway, interurban/ urban primary road and interurban/ urban secondary road. Typical accident figures and accident cost figures were calculated for crossings and junctions with and without traffic lights, as well as for roundabouts with 3 and 4 or 5 linked roads.