Control strategies of traffic signal timing transition for emergency vehicle preemption

Emergency vehicle (EV) operation saves lives and reduces property damage. This paper reports two new control strategies for EV signal pre‐emption (EVSP) that reduce the response time and minimize the impact of EV operation on general traffic. A real‐time control strategy is developed that enables signal transitioning from normal operation to EVSP (transition 1) so that the approaching EV can cross the intersection safely at its operating speed and also the impact of the EVSP on general traffic is decreased. The green time that is not required for the EV is dynamically allotted to the traffic on the cross road by taking into account the prevailing traffic condition at the intersection and the state of signal indication. The second control strategy, implemented by an optimal control algorithm, is used for the signal transitioning from the EVSP back to normal operation (transition 2). A two‐phase algorithm, consisting of a relaxation method and a stepwise search strategy, is adopted to overcome the difficulty in solving the optimal control model, which results from the interrelationship between successive signal sequences. Software was developed in the MATLAB environment for simulations of the EVSP process under different signal timing transitioning control strategies. Results indicate that the real‐time control and the optimal control strategies and their associated methods perform better than the commonly used existing approaches. It is also demonstrated that the two control strategies are applicable to different traffic conditions up to and slightly over‐saturated level, and can be used to deal with a single EVSP occurrence as well as multiple EVSP occurrences.