Comparative Traffic Operational Analysis Between Turboroundabouts and Roundabouts.

This paper presents a comparative analysis between the traffic performances of turboroundabouts and roundabouts in terms of capacity, delays and queue lengths. First, roundabouts and turboroundabouts with different geometries and different traffic demands are selected, thus presenting a wide range of operational conditions. As calculation procedure of turboroundaboutcapacity, a recent German procedure for roundabouts, which has been adapted for turboroundabouts, was chosen. One found that the capacity of a turboroundabout entry is higher when the flows on the circle inner lane are high and the flows on the circle outer lane are low or lower-middle. Under undersaturation or saturation conditions of at least one of the entries, the total capacity of turboroundabouts is lower than the capacity of roundabouts when traffic conditions are very unbalanced and two one-way two-lane roads converge into the intersection. When traffic conditions and geometric configurations are different, one must evaluate capacity on a case-to-case basis. To calculate capacity, sensitivity analysis regarding psychotechnical times and percentages of entry lane selection are also performed. Waiting times and queue lengths are, in almost all the situations analyzed, higher for turboroundabouts in comparison with roundabouts.