Safety evaluation of continuous green T intersections.
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Safety evaluation of continuous green T intersections.

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      The continuous green T (CGT) intersection is characterized by a channelized left-turn movement from the minor street approach onto the major street, along with a continuous through movement on the major street. The continuous through movement typically has a green through arrow indicator to inform drivers that they do not have to stop. Past research has consistently shown that there are operational and environmental benefits to implementing this intersection form at three-leg locations when compared with a conventional signalized T intersection. These benefits include reduced delay, fuel consumption, and emissions. The safety effects of the conventional signalized T intersection are less clear. Past research has been limited to a small sample of intersections in a single State and considered only comparisons in reported crashes between adjacent lanes on the major street approach (continuous flow versus the opposing through lanes). The study designs used in past safety research were limited to simple statistical comparisons using reported crash data. The present study overcomes past safety research evaluations by using a propensity scores-potential outcomes framework to compare the safety performance of the CGT with conventional signalized T intersections using 30 treatment and 38 comparison sites from Florida and 16 treatment and 21 comparison sites from South Carolina. The results showed that the expected total, fatal and injury, and target crash (rear-end, angle, and sideswipe) frequencies were lower at the CGT intersection relative to the conventional signalized T intersection (CMFs of 0.958 (95 percent confidence interval (CI) = 0.772–1.189), 0.846 (95 percent CI = 0.651–1.099), and 0.920 (95 percent CI = 0.714–1.185), respectively). Further, the benefit-cost analysis indicated that the CGT intersection is a cost-effective alternative to the traditional, signalized T intersection. The results of the safety evaluation were not statistically significant, likely due to a small sample of treatments. When considered in combination with the operational and environmental benefits, the CGT intersection appears to be a viable alternative intersection form, although anecdotal feedback from South Carolina and Florida indicate that some non-motorized users (pedestrians and bicyclists) find it challenging to cross the continuous flow through lanes on the major street approach when traffic volumes limit the number or size of available gaps.
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