CAPACITY MODELS FOR MULTILANE ROUNDABOUTS AND THEIR EVALUATION USING MICROSCOPIC SIMULATION MODELS

Compared to previous versions of the manual, the Highway Capacity Manual 2010 has provided more comprehensive capacity models for single and multilane roundabouts. The Highway Capacity Manual 2010 multilane roundabout capacity models are limited to two-by-two lanes, that is, two entry lanes and two circulating lanes. These capacity models are not valid for the three-by-three–lane roundabouts (three entry lanes and three circulating lanes) due to different traffic flow characteristics and features. This limitation of the Highway Capacity Manual 2010 model is also clearly mentioned in the manual. In this research, capacity models and curves were developed for three-by-three–lane roundabouts. More than 168 hours of video recordings were done on 12 three-by-three–lane roundabouts. The extracted data from the video recordings was used to understand the traffic operations and to develop the capacity models. It was found that lane utilization of the outermost circulating lane was low, and drivers preferred to use the middle entry lane for through movements as compared to the other two lanes. Based on the performance and usefulness, exponential regression models were selected for capacity estimation. The capacity curves were developed for the entry approach and for each entry lane of the three-by-three–lane roundabout. These models were used to estimate the follow-up headway and critical gap. The output of the proposed models showed that the entry volume decreases with the increase of the circulating flow at the three-by-three–lane roundabouts. The proposed models were also validated using a microscopic traffic-simulation model. A close association was found between outputs from both models. Transportation engineers can use the vii capacity models and curves presented in this research to perform the three-by-three–lane roundabout capacity analysis. Keywords: Three-by-three–lane roundabout, multilane roundabout, VisSim, capacity models, capacity curves, conflict areas