Determination of the Existing Sight Distance and its Influence on the Speed on Highways

Abstract

The main task of a high-quality road design is to provide the driver with a clear information about the course of the road at an early stage. The good visual guidance on highways is a prerequisite for adequate driving safety. Therefore, the sight distance has a significant impact on traffic safety, performance, speed behavior and driving comfort. At least the required stopping sight distance should always be guaranteed on highways, in order to ensure traffic safety and quality of traffic flow. The purpose of the stopping sight distance is to enable the driver to stop in time in front of an unexpected obstacle with a certain height on the road or in front of the end of a traffic jam. In addition, as a regulating element in road design, it is intended to ensure early driver information and orientation. The driver reacts to external influences by choosing the speed and changing it. Therefore, the speed parameter itself represents the best and most suitable evaluation criterion for driving behavior. In this paper, it has been succeeded to prove, that the existing sight distance exerts an influence on the speed on highways in Germany. A clear increase in the 85th percentile speed was determined with an increasing existing sight distance up to 400 m. At a sight distance above 400 m V85 remained almost constant. An increase in the 15th percentile speed was only noticeable up to a sight distance of 300-350 m, after which V15 remained at the same level.