Abstract

A model of distribution of the time intervals between the vehicles on a roundabout envelope, that is applied to perform the calculations of the traffic conditions and the capacities of small roundabouts, has a significant impact on the accuracy of these calculations. In Poland such distribution is given by the exponential model and applied for calculations of capacity of the roundabouts. The distribution of the real time intervals between vehicles on the roundabout envelopes deviates from the exponential model as it has been shown in numerous publications. Using it for the average and higher volumes of the traffic flow may lead to the large inaccuracies of calculations. The main objective of this work is to assess the usefulness of theoretical models of a random variable used to describe the time intervals between the vehicles on a roundabout envelope. It has been demonstrated that the best one for such purpose is a displaced exponential distribution and therefore it is recommended to be used for the analyses of the traffic conditions and capacities of small roundabouts in Poland. The calculated minimal time interval between the vehicles as a function of the traffic volume, and the passenger car equivalents for heavy vehicles on the roundabout envelope are also presented.