Evaluation of the Operational Performance of Continuous Green T-Intersection under Different Levels of Congestion

Zawawa, Ghayda; Naghawi, Hana · 2019 · Crossref

DOI: 10.3311/pptr.14032

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Summary

This study evaluates the operational efficiency of the Continuous Green T-intersection (CGT), an unconventional design proposed by the Federal Highway Administration to reduce conflict severity, compared to a conventional signalized T-intersection. The research addresses the limitations of conventional intersections under varying congestion levels, specifically investigating whether the CGT design offers superior performance across different traffic volumes. The motivation stems from the need to improve intersection safety and efficiency, as conventional measures often yield diminishing results under heavy traffic conditions. The methodology employed microscopic traffic simulation using Synchro.8 software to model two hypothetical intersection designs: a conventional three-leg signalized intersection and a CGT-intersection. Both models featured an eight-lane divided arterial road intersecting with a four-lane undivided collector road at a 90-degree angle, adhering to AASHTO geometric standards. The researchers created 48 hypothetical scenarios (24 for each design) by varying approach volumes and turning percentages to simulate stable (1200 vph on arterial) and unstable (2000 vph on arterial) traffic conditions, alongside varying collector road volumes (800–1000 vph) and left-turn percentages. Performance was assessed using four measures of effectiveness: total intersection delay, Level of Service (LOS), maximum queue length, and volume-to-capacity (v/c) ratio. The results indicate that the CGT-intersection performs significantly better than the conventional design under stable traffic conditions. In these scenarios, the CGT design reduced intersection delay by 16% to 37%, improved LOS, and decreased maximum queue lengths on the arterial and collector roads by up to 40% and 37%, respectively. However, under unstable traffic conditions, particularly those with high left-turn volumes from the arterial road, the CGT-intersection failed to provide benefits. In these heavy traffic scenarios, the CGT design increased intersection delay by up to 26% and resulted in LOS F conditions, indicating system breakdown. While the CGT design reduced queue lengths on the collector road during unstable conditions, it often increased or failed to reduce queues on the arterial road when left-turn demand was high. The study concludes that the CGT-intersection is an effective solution for improving operational performance under stable traffic conditions but is not suitable for intersections experiencing heavy traffic volumes or high left-turn demands. The findings suggest that while the design reduces conflicts and delay in moderate traffic, it lacks the capacity to handle unstable flow conditions effectively, leading to increased delays and poor service levels. This implies that the implementation of CGT-intersections should be carefully considered based on specific traffic volume characteristics, particularly avoiding locations with high congestion or significant left-turn movements.

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• intersection design