TRAFFIC SAFETY ON TWO-LANE RURAL ROADS - NEW CONCEPTS AND FINDINGS

Two-lane rural roads have by far the highest accident rate of any class of rural highways. Accident statistics reveal that with respect to the accident type mainly run-off-the-road accidents occur on these roads. Often the driver loses control of the vehicle because the selected speed did not correspond to the alignment of the roadway. Nearly half of the accidents of non-built-up roads occur on curved roadway sections. Obviously many curves, especially on old alignments are dangerous spots and have to be improved by safety management measures aimed at reducing accident frequency and severity. Many investigations in the last years show that abrupt changes in operating speed lead to accidents. Speed inconsistencies may be largely caused by sudden changes in road characteristics. Regarding this, it is very important to elaborate appropriate procedures to evaluate the road geometric with special emphasis on traffic safety. However, under an economic point of view, it is evident that by far not all safety deficits on two lane rural roads can be tackled through new alignments or RRR projects. More and more low cost measurements have to be used in order to quickly improve the traffic safety. A new approach, developed at the Dresden University of Technology, uses the strategy of the so-called "driving conflict technique" to investigate possible safety conflicts between the driver and the road. It contains three different levels which are weighted within the approach according to the following order: (1) quality of the alignment considering the horizontal and vertical alignment as well as the cross section and the road appearance expressed by the three dimensional alignment; (2) level of service; and (3) driving dynamic relationships between the vehicle and the road. Because curves still are a considerable traffic safety problem it is necessary to elaborate a procedure to identify safety deficits on curves reliably and determine appropriate countermeasures. The newly developed method contains three components: the Accident Analysis Model, the Curve Geometric Model, and the Curve Driving Behavior Model. An additional fourth component called the Measurement Set Model deals with the selection of appropriate low cost measurements in curves based on the analysis results of the above models. Because both new approaches are recently finished, this paper focuses on the discussion of their principal concepts.