Traffic safety and traffic flow on b2+1-routes carrying mixed traffic.

In order to improve traffic safety and the quality of service on single carriageway rural roads, cross sections with three lanes (b2+1-routes) are becoming more popular. In accordance with the current German guidelines these roads have to be operated for motor vehicle traffic only. The increasing number of three-lane rural roads raises the question whether these roads can generally be released to mixed traffic and whether any boundary conditions need to be taken into account in this case. If slow traffic does not turn out to have any long-term negative influence on safety or flow on such routes, the range of application of this cross section could be extended considerably thus saving construction costs and land use for separate route networks in individual cases. The investigation of traffic flow and traffic safety was carried out on seven roads with a total length of 58.8 km. The average daily traffic (ADT) of these roads varies from 10,000 up to 16,500 vehicles per day. The traffic flow has been analyzed by following free flowing cars. Additionally, the number of vehicles and their speed were recorded at one cross section of each road. One result is that on the investigated roads there is only little impact of slow vehicles on traffic flow. The number of cars driving slower than 60 km/h is less than 1%. All accident reports of a three year period of time have been analyzed, in total 401 accidents. The number of accidents per road varies widely.