Two-Lane Rural Highways: The German Experience

Abstract

A series of investigations was performed in Germany to understand traffic operations on two-lane highways and to make the experiences accessible for traffic performance analysis in practice. As an initial step, traffic flow on several sections of rural two-lane highways was observed. The observations led to a set of empirical speed-flow relationships for highways of different characteristics. On the basis of these results, a microscopic simulation model was calibrated. The model was able to produce a comprehensive set of speed-flow diagrams for all kinds of rural two-lane highways. The diagrams revealed several unexpected properties: a concave shape and nonlinear influences of the external geometric parameters such as curvature or gradients. The simulated results were then approximated by a simple quadratic equation with the parameters depending on geometric conditions and the percentage of heavy vehicles. Thus, the speed-flow diagrams were obtained for the German Highway Capacity Manual. In this case den...