The improvement of road safety is an important challenge to infrastructure engineering. Various safety procedures with different objectives and application fields have been developed in order to contribute to a further decline of especially accidents with fatalities. On the one hand there are procedures which analyse the current situation and are often realised for and applied to road operation or are already integrated in the planning process. They are helpful tools for several users such as road engineers or road managers. On the other hand, accident prediction models and Safety Performance Functions have been developed in order to estimate possible impacts of road infrastructure on road safety. The main difference is that they are based on mathematic models derived from scientific investigations and calculate statistically possible effects. Accidents are influenced and caused by many various factors. The interaction between driver, vehicle and environment is complex and so far there is no model which considers all aspects of impacts. But numerous research studies have shown that beside properties of infrastructure also the behaviour of drivers has to be taken into account in order to analyse accident causes more accurately. Therefore, the investigation methodology of work package ten considers both the impacts of road infrastructure parameters as well as the behaviour of drivers. This was achieved by the definition of section types which classify the existing horizontal alignment of roads based on driving behaviour models. A section is defined as stretch of a certain length and it has almost constant impact on speed due to its geometric properties. Investigations of accident structure have pointed out that especially single accidents like driving accidents and accidents in longitudinal direction like passing accidents or rear end collisions have the largest portion on the total number of fatalities on secondary rural roads. For that reason, the development of the Safety Performance Function is based on the investigation and evaluation of selected accident types which are connected to the alignment of roads. For the geometric parameters curve radius, curvature change rate and furthermore, for speed differences between consecutive elements correlation models have been developed which calculate estimated accident rates and accident cost rates. Additionally, also the impacts of traffic volume and road width were considered. In order to evaluate the calculated results, a comparison to average accident rates and accident cost rates was suggested which shows possible safety potentials within the investigation area. The derived results show that the investigation methodology is appropriate. Also the section definition and the pre-selection of accident types were approved since it lead to more accurate results and better correlation factors. (Author/publisher)
Samenvatting