Improvement Solutions for Traffic Operation and Geometric Design of Roundabouts

Intersections are the main gorge of traffic in the cities and roundabouts have become one of the popular options for intersections traffic management because of their positive features in terms of capacity, performance and safety. Conducted comparisons between controlled intersections and roundabouts by different researchers shows that roundabouts have lower latency and greater safety than intersections. This operation depends largely on their geometric design. Older roundabouts are facing traffic and safety problems due to poor design of entries, exits, circulating lane width, pedestrian crossing location and central island. Therefore, they are close to locking in peak hours and have low safety in off-peak hours. In fact, with the presence of weaving movements, high difference in speed and improper angle between entry and circulating approach, failure to provide adequate stopping sight distances, inadequate angles between the approaches and the lack of proper signs and line marking, the operation of older roundabouts have changed to the one's for the traffic circles. Therefore, this study attempts to identify the weaknesses in the design and performance of roundabouts and provide solutions for resolving them by understanding the characteristics of modern roundabouts and their differences to other traffic circles and also studying the previous field studies on roundabouts in different cities of Iran and other countries.