PRIORITY METERING CONTROL FOR AN URBAN CIRCULAR INTERSECTION

Abstract

Circular intersections have been used in transportation systems since the 1900s. Threetypes of circular intersections have been used in the United States: traffic circles, rotaries androundabouts. While the use of traffic circles and rotaries in recent decades was found to haveresulted in high crash rates, safety issues have been mitigated for roundabouts through the use ofimproved geometric designs.Nevertheless, all three types of circular intersections face capacity problems duringperiods of high traffic volume, resulting in long queues and delays. Signal metering wasintroduced to reduce long queues and delays on the dominant approaches to circularintersections by stopping the flow of traffic from other approaches. This methodology was foundto ease congestion for circular intersections with historically high traffic volumes. However, mostsignal metering at those intersections employ fixed signal timing, in which the metering rate is notresponsive to changes in traffic condition. This study investigates the performance of an adaptivemetering system for circular intersections. The system was implemented on a real traffic circlehaving high and unbalanced volumes. The model was calibrated, and a case study was simulatedfor peak-hour traffic conditions. Using the PTV VISSIM application programming interface, thealgorithm was tested and the performance of the system was compared to the current intersectionoperation. The results showed that adaptive metering can significantly reduce delays and queuesat a traffic circle. This preliminary study can be a useful reference for the development of prioritycontrolledcircular intersections.