Improving the Capacity and Level of Service at the Sixth Circle in Jordan by Using Traffic Signals and Roundabout Metering Approach

Khliefat, Ibrahim; Naser, Mohammed; Alhomaidat, Fadi; Hanandeh, Shadi · 2021 · Crossref

DOI: 10.2174/1874447802115010069

archive: archived pipeline: cataloged verified

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Summary

This study addresses the severe traffic congestion at the Sixth Circle in Amman, Jordan, a major intersection linking four commercial areas. The research aims to improve the capacity and Level of Service (LOS) of this roundabout by evaluating traditional traffic signals and a novel roundabout metering approach using adaptive signals. The motivation stems from the prevalence of high congestion on Amman’s arterial network and the lack of comprehensive signal tactics for traffic management in Jordan. The methodology employed microsimulation modeling using VISSIM software, integrated with a custom C++ program to control adaptive signal logic. The study site was selected based on data from the Greater Amman Municipality, which identified the Sixth Circle as highly congested. Geometric data were extracted via Google Earth, while traffic volume and flow data were collected from ground sensors and field observations. The VISSIM model was calibrated using field-measured macroscopic parameters, specifically travel times and queue lengths, to ensure the simulation accurately replicated real-world traffic dynamics. The researchers tested three primary scenarios: the existing unsignalized roundabout, a converted four-legged signalized intersection, and the original roundabout equipped with adaptive metering signals controlled by ground detectors. The results indicated that the existing unsignalized roundabout performed at LOS F, characterized by significant delays and queue lengths ranging from 115 to 179 meters. Converting the roundabout to a signalized intersection with a 90-second cycle length improved performance to LOS D. However, the adaptive signal scenario yielded the most significant improvements. By using C++ to process real-time queue data from ground detectors, the system dynamically adjusted signal timing, effectively metering entry into the roundabout. This approach reduced average queue lengths by over 100%, dropping from 221.3 meters to 76.2 meters, and significantly increased average flow rates. The adaptive system maintained an LOS between B and C by continuously updating signal phases based on detected congestion, preventing the blockage of downstream approaches. The significance of this study lies in demonstrating that adaptive roundabout metering is a highly effective, low-cost solution for managing congestion at complex urban intersections. The integration of VISSIM with C++ allows for real-time traffic management that traditional fixed-time signals cannot achieve. The findings suggest that such adaptive systems can substantially reduce delays and improve traffic flow efficiency, offering a viable alternative to costly geometric modifications or full intersection conversions. This approach provides transportation planners with a scalable tool for enhancing urban mobility and reducing the economic and social impacts of traffic congestion.

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• intersection design