System-Wide Impacts of Green Extension Transit Signal Priority

Basic green extension transit signal priority (TSP) was implemented on U.S. Route 1 in the Northern Virginia Area. The study investigated the system-wide benefits of green extension TSP operation on the U.S. Route 1 corridor using the INTEGRATION microscopic traffic simulation software. The simulation results indicated that transit signal priority did not result in statistically significant changes in transit vehicle, auto, or system-wide travel times (differences less than 1%). Furthermore, a paired t-test concluded that basic green-extension TSP did not increase side-street queue lengths. The simulation results indicated that the transit priority system generally benefited transit vehicles but did not guarantee system-wide benefits. Maximum travel-time savings in the order of 3.40% were observed with the provision of green extension TSP. These findings are a result of the unique characteristics of the study corridor and the TSP logic implemented. Specifically, the study corridor operated under a long cycle length of 180 seconds with most of the green time assigned to U.S Route 1 (on average 76 percent). Thus the probability of receiving a green extension was relatively small (less than 3% per intersection for each transit vehicle). Furthermore, even when a TSP-equipped vehicle arrived during a red indication, the stopped delay was relatively short because most of the cycle time was assigned to U.S. Route 1