Prediction Occurrence of Crashes at Roundabouts by Gamma Modelling Technique

The annual costs of traffic accidents beyond the economic, social etc impose on society. Intersections constitute only a small part of the road transportation network, yet intersection accidents constitute a significant portion of the total accidents. Roundabouts have become a common type of intersection design in many countries. Considerable differences in the number of Roundabouts crashes according to structural variations in roundabouts safety performance and also according to exposure elements (Traffic Volume). One of the aims this paper is to explore structural relationships between geometric designs with features of the traffic on the one hand and the level of safety of roundabouts on the other hand. In this study, 16 roundabouts in Tehran, Iran as example have been investigated. Vulnerable road users such as motorcycles and pedestrians often involved in injury crashes at roundabouts. Gamma modelling technique were used. Based on the final model, changes in the rate of accidents at roundabouts are often caused by geometrical factors and exposure elements.