Emergency vehicles are essential means of timely and urgent rescue. Emergency vehicle preemption (EVP), the most common form of traffic signal preemption in urban areas, is usually activated to grant emergency vehicles the right of way at signalized intersections by abruptly terminating the current signal timing plan. However, such mandatory signal changes can disrupt arterial signal coordination by terminating the current timing plan at each intersection and triggering unexpected transitions in traffic signal controllers at the end of the preemption. To comprehensively analyze and minimize such negative impacts caused by EVP, this research summarized optical-based EVP operations along with preemption modules in Trafficware 980 ATC V76 signal controllers to illustrate their negative impacts on arterial signal coordination. Hardware-In-the-Loop Simulation (HILS) was utilized to evaluate and compare five exit strategies of EVP in Trafficware 980 ATC V76 signal controllers: no exit phase, exit to fixed phases, exit to fixed phases (end dwell), Coord+Preempt and the dynamic threshold timer under defined five simulation scenarios with different numbers of preemptions. The evaluations were carried out using a signalized arterial, N. McCarran Blvd, which includes two intersections in Reno, Nevada.It was found that the extent of negative impacts on arterial signal coordination was highly influenced by preemption activation points, routes of the emergency vehicle, the selection of an exit strategy and the number of preemptions. Average vehicle delay on the non-preempted arterial movements tended to rise with an increasing number of preemptions. Among those five exit strategies, no exit phase strategy delivered worse performance than others especially on the arterial through movements. End dwell and the dynamic threshold timer provided more flexibility of phase return than exiting to fixed phases only, which potentially enhances performance on the main-street and side-streets. Coord+Preempt was found to be the best exit strategy to be implemented due to its ability to proceed back to the background coordination without transition and produce the overall minimal delay for all turning movements under different numbers of preemptions
