Evaluating the Impacts of Different Exit Strategies of Emergency Vehicle Preemption on Arterial Signal Coordination: A Case Study in Reno, Nevada

Emergency vehicle preemption (EVP), a common traffic signal preemption in urban areas, is used to prioritize the right-of-way to emergency vehicles at signalized intersections by terminating active signal timing plans and running preemption plans. However, such mandatory signal changes can disrupt arterial signal coordination when an emergency vehicle travels through a well-coordinated signalized arterial. The research need has emerged to evaluate and minimize such disruptions to arterial signal coordination. Therefore, this research summarizes EVP operations along with preemption modules in North America Econolite Cobalt signal controllers (EOS software version) and investigates five available EVP exit strategies to minimize disruptions: return to defined phases, return to coordinated operations, return to free operations, return to first skipped phase, and return to the most delayed phase. The impacts of five exit strategies on arterial signal coordination are evaluated and compared on a signalized arterial through hardware-in-the-loop simulation (HILS) in four different simulation scenarios. From simulation results, it is found that EVP tends to worsen arterial and intersection operations for all five EVP exit strategies by increasing the arterial travel times and the total vehicle movement delay at preempted coordinated intersections. The performance of different EVP exit strategies is influenced by the route of the emergency vehicle and the EVP activation point. Furthermore, the selection of an EVP exit strategy depends on different operational objectives after EVP. When recovering arterial signal progression becomes the primary objective, the return to coordinated operations exit strategy is recommended to be selected at intersections to minimize disruptions. The return to the free operations exit strategy is recommended to avoid queue spillover and phase split failure issues at intersections when improving the intersection-level performance turns out to be the overarching goal.

Traffic signal preemption systems play an essential role in emergency response management in terms of shortened response times, improved traffic safety, and potential cost savings. As one of the common traffic signal preemptions in urban areas, EVP functions by prioritizing the right-of-way to emergency vehicles through green signal indications at signalized intersections. Although emergency vehicles benefit from signal preemption at intersections, the mandatory signal changes caused by EVP can disrupt arterial signal coordination when emergency vehicles travel through a well-coordinated signalized arterial. There exists a research need to evaluate and minimize such disruptions caused by EVP on arterial signal coordination. Therefore, this research summarizes EVP operations along with preemption modules in signal controllers and investigates five available EVP exit strategies to mitigate disruptions of EVP on arterial signal coordination. The summarized EVP operations in signal controllers and recommendations for use regarding EVP exit strategies in this research serve as a valuable reference for practitioners in real-world EVP system management and optimization.