Enhancement of Traffic Performance for Signalized Roundabout Intersections

Abstract

Signalized roundabouts are used to manage high traffic demand, but they may still experience congestion, queues, and high delay due to unbalanced traffic volumes, turning movements, circulating flow interaction, weaving movements, signal timing, and geometry. This paper evaluates the operational performance of four signalized roundabouts in 10th of Ramadan City: Al-Kafrawy, Al-Rwad, El-Nasagon El-Sharqion, and El-Safera Aziza. It also examines the applicability of the HCM signalized intersection delay procedure by comparing HCM delay estimates with field delay measurements and calibrated VISSIM outputs. Field videos were analyzed to extract traffic volumes, turning movements, vehicle classifications, and delay values. VISSIM models were developed, calibrated, and validated using field delay data, while the agreement among field, VISSIM, and HCM results was assessed using descriptive measures, correlation analysis, and regression modeling. Two enhancement scenarios were also tested: signal timing optimization and conversion to a conventional signalized intersection. The results showed that calibrated VISSIM closely represented field delay, with a mean delay of 52.92 s/veh compared with 50.61 s/veh in the field, while HCM produced a higher mean delay of 67.39 s/veh. Regression analysis showed stronger agreement for field–VISSIM delay (R² = 0.9937) than field–HCM delay (R² = 0.9303). The enhancement results indicated that conversion to a conventional signalized intersection achieved greater delay reduction than signal timing optimization, especially where through movement was dominant.