Orientation Sight Distance--Definition and Evaluation

In the current German design guidelines (RAS-L) geometrical models of sight distance are considered excludingly. The factor determining the safety of a road is the stopping sight distance. It marks the minimum of sight quality which is to be available to the driver at any time. This demand constitutes the basis for the calculation of design elements such as curve radii and vertical curvatures. Technical improvements in the last years and especially the widely-used antilock brake system (ABS) have led to better driving dynamic characteristics, which seems to support a distinctly smaller stopping distance. Contrary to that, stands the demand for early recognizability and comprehensibility of the roadside environment by the driver. As they do not always expect emerging obstacles, drivers will not adjust their speed to the existing stopping distance. In reality, the entirety of information offered by the roadside environment exerts vital influence on driving behavior. Therefore, the goal of this research project was to determine the influence of sight conditions on driving behavior. The emphasis therefore is on investigation of perception behavior as well as the psychological demand on the driver at different sight distances. As a result, the existing geometrical models of sight distance dimensioning are to be supplemented by basic psychophysiological approaches or rather a behavior-based model of orientation sight distance. Investigations include the analysis of gaze behavior of drivers in a real car and in a driving simulator. The real test tracks are reproduced in a sophisticated model for the simulator, which provides the possibility to vary particular parameters, especially available sight distances, and to quantify exactly the effects on driver workload, perception and driving behavior. As a result of this project a model of orientation sight distance combining both psychological and design relevant findings will be developed. In the course of the revision of the German design guidelines the new model is to supplement currently valid geometrical models.