Verification of the existing model for passing sight distance on single two-lane rural carriageways

Abstract

In 2012, new rural road design guidelines (RAL) has been released in Germany. They define different types of roads including different principles for passing. On new roads with a high road function level, passing is safeguarded by passing lanes. However, passing lanes cannot be recommended as a standard on each road type. For roads with a lower road function level and on most of the existing rural road network, passing is permitted by using the oncoming traffic lane. The passing sight distance used today is based on a geometrical model which has been the subject of an empirical research in 1986. Because of the change in the vehicle fleet the passing sight distance model needs to be verified and updated. For this purpose, passing maneuvers are recorded by using a drone. The methodology allows capturing the entire passing maneuver including the approach of the opposing traffic. Thereby, the road geometry as well as traffic parameters (average annual daily traffic - AADT, heavy good vehicles - HGV) are considered. Overall, more than 1.100 passing maneuvers have been captured and analyzed. As a research result, recommendations for the required passing sight distance on single two lane rural roads will be given.