The first modern roundabout in Kansas was constructed in Manhattan in 1997. The operation of this roundabout intersection was compared with two comparable 2-way STOP controlled intersections and with different traffic control scenarios. Traffic count data was collected with a 360-degree omnidirectional video camera. Traffic data was evaluated with the computer program SIDRA (Signalized and Unsignalized Intersection Design and Research Aide). The analysis results were statistically tested to determine which intersection(s) operated statistically better. When compared to the two comparable 2-way STOP intersections, the roundabout performed worse or the same for three of the evaluative measures: average delay, 95 percentile queue and proportion stopped. The roundabout operated better with regard to maximum approach delay, maximum proportion stopped and degree of saturation. The roundabout intersection was also evaluated under three different traffic control scenarios: two-way STOP, four-way STOP and four-way STOP with separate left turn lanes. This evaluation found the roundabout to operate better than the other alternatives with respect to all measures. Prior to roundabout construction, the intersection experienced an average of 3 traffic crashes, with at least one injury per year. Since completion in November 1997, the roundabout has experienced no reported traffic crashes. (Author/publisher)
Abstract