Roundabouts and Pedestrian Capacity: A Simulation Analysis 5,685 words

Since the emergence of modern roundabouts in the U.S., vehicle safety and pedestrian safety have become major issues regarding the effectiveness of roundabout performance. Sufficient data exist to estimate vehicle safety at roundabouts, as well as level of service and capacity. However, little U.S. data exist for pedestrian safety and capacity at roundabouts, especially for those replacing conventional intersections. This paper demonstrates how simulation applied to proposed roundabouts can help overcome the pedestrian data deficiency and indicate whether or not a proposed roundabout can accommodate expected pedestrian demand as a precursor to safety analysis. This paper develops a micro-simulation of a case study four-lane signalized intersection with heavy pedestrian volumes that is scheduled for reconstruction as a single-lane roundabout. The simulation results are used to estimate pedestrian capacity for the proposed roundabout for different traffic demands and typical pedestrian reaction times and walking speeds including those for disabled pedestrians. The method shows that for pedestrians with typical reaction times of 3.2 seconds and walk speeds of 4 ft/sec, the proposed roundabout pedestrian capacity is adequate compared to that of the signalized intersection with "Flashing Don't Walk" signals when the roundabout volume is about 1,685 vehicles per hour (70% of the original intersection volume). At similar traffic volumes a sensitivity analysis demonstrates that roundabout pedestrian capacity remains greater than that for the conventional intersection without a pedestrian signal and for cases where reaction times and walk speeds reflect slow pedestrians. In concept the demonstrated roundabout pedestrian capacity analysis should follow a conventional intersection analysis that demonstrates the technical feasibility of the roundabout to handle traffic demand. Following the roundabout pedestrian capacity analysis, a pedestrian safety analysis based on local accident reports, field data and anticipated accident models from the literature should be undertaken. The procedure represents a practical method for justifying to decision-makers the effectiveness of a roundabout where the vehicle traffic and pedestrian activity are high.