|M.Sc Student||Masarwe Ashraf|
|Subject||Capacity Comparisons of Unsignalized Intersections and|
Roundabouts and Feasible Operating Ranges
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Abishai Polus|
This study presents a comparison of methods and models for estimating capacity, queue length, delay, stop ratio, and level of saturation at roundabouts and at unsignalized intersections. This comparison will yield the range of volumes at which roundabouts are preferable to unsignalized intersections, and vice versa. To carry out this research, an analysis was conducted according to the delay and the capacity functions under the assumptions of critical gaps and opposing volumes in accordance with Highway Capacity Manual 2000 for unsignalized intersections. For roundabouts, the models chosen were those calibrated by Polus and Shmueli (1997, 2000), the German model, the American model, and the Australian models. Calculations were made according to HCS 2000 programs and the SIDRA computer program.
It was found that at every range of opposing volumes, the roundabout receives preference in capacity over conventional, unsignalized intersections. In a comparison of roundabouts and conventional intersections, queue lengths at a right turn at every range of opposing volumes are very similar, though a little shorter at the conventional intersection. By contrast, queue lengths at a left turn are shorter at a roundabout than at a conventional intersection.
The delay to vehicles in a roundabout compared to an unsignalized intersection, without connection to the type of turn, is smaller. The stop ratio was smaller at a roundabout than at an unsignalized intersection at all volume ranges. The saturation level at a roundabout was smaller than at an unsignalized intersection, thus giving preference to roundabouts at all volumes.