Demands for overtaking result from speed differences in traffic flow. The estimation of overtaking possibilities is based on the time-gap distribution of the oncoming traffic flow and on the probability of having an overtaking sight distance. The resulting number of actual overtakings and vehicles in platoons is dependent on the relation between the total overtaking possibility and the total overtaking demand. The risk in overtaking can be related to the risk difference in and outside platoons. Thus it can be calculated, in which condition an overtaking decreases the total accident risk. The platooning rate, defined as the ratio between the actual platoon percentage in the observed flow and a theoretical platoon percentage in an assumed flow with the same volume and totally independent time-gaps, is proposed as a new measure of trafficability on two-lane roads.
Abstract