Document Type : Research Paper



Roundabout is one of the most effective intersection control methods in the world. Although, they have often been used in Iran, but, the methods which are proposed to analyze roundabouts are very old and new regulations are not implemented for analyzing modern roundabouts. There are strong needs to apply new modern analyzing methods for studying roundabouts in Iran. Also, these methods should be compared with other methods for controlling intersections. The results from previous studies show that roundabouts perform better than the intersection with two-way stop and all-way stop control in various cases. The most important aim of this research is to compare the capacity and delay of roundabout with signalized intersection at the same conditions. In this paper, the methods which are applied in the developed countries for calculating the capacity and delay of roundabout are considered and the most effective and suitable one is chosen for using in Iran. The method of Australia was selected and proposed for analyzing roundabouts. For analyzing the capacity and the delay of signalized intersection the HiCAP software was used. This software works based on HCM2000 theoretical model. Two signalized intersection of Isfahan city were selected for the case study. The roundabout plan was used in the same situations with the same space and traffic data. The diagram of entrance delay and capacity of roundabout and signalized intersection was obtained and analyzed. One of the main results of this analysis is that a two-lane roundabout in same space intersection with inscribed circle diameter of 55 to 60 meter can pass about 3400 vehicles per hour with lower delay comparing to intersection. Another result is preference of roundabouts in low and medium volumes comparing to intersections. In such volumes roundabouts have very low delays comparing to intersections. As an important point, this research shows capability of the selected method for analyzing roundabout and represents formula calibration with regard to Iran conditions.