TRANSIT SIGNAL PRIORITY: 'GREEN EXTENSION' BENEFITS IN CONGESTED CORRIDORS

This paper describes how transportation engineers and planners worldwide are faced with the challenge of improving transit services in urban areas utilizing low cost means. Transit signal priority is considered to be an effective way to improve transit service reliability and efficiency. In light of the interest in testing and deploying transit signal priority on a major arterial in Northern Virginia, this research focuses on the impacts of transit signal priority along the U.S.1 corridor in Fairfax County, in terms of benefits to transit and impacts on other traffic. Using a simulation tool, VISSIM, these impacts were assessed considering a ten second green extension priority strategy. Also, this assessment is being supported by a field study giving researchers an opportunity to compare simulation and field study results. The results of the simulation analysis indicated that the Fairfax Connector buses benefit from the green extension strategy with little to no impact on the other non-transit traffic. Overall, improvements of 3.61% were found for bus service reliability and 2.64% for bus efficiency, while negative impacts were found in the form of increases in queue lengths on side streets by a maximum value of approximately one vehicle. Preliminary field results show a comparable improvement in bus efficiency of 2.38%. While evaluating the impacts of provision of priority to transit buses this research emphasizes that 'green extension' strategy provides constant benefits with little to no disbenefit to other traffic. This research tries to provide a comparative depiction of results consistent with past studies showing 'green extension' as a viable option, even in most congested corridors without disrupting non-transit traffic.