Investigation on the exit phase controls for emergency vehicle preemption

Abstract

Many traffic signal control systems used in the U.S. have Emergency Vehicle Preemption (EVP) systems that change traffic signals to clear an intersection for emergency vehicles. However, one of the challenges of implementing EVP under coordinated-actuated signal systems is selecting the best recovery method at the end of preemption such that disruptions to normal traffic signal operations may be minimized. To this end, there have been lots of research efforts which have compared the performances of various transition methods after EVP operations using microscopic traffic simulation models, Hardware-in-the-loop Simulations (HILS) or softwarein-the-loop simulations (SILS). However, few attempted to implement exit phase controls during the EVP operations, which is available in recent advanced traffic controllers such as the ASC/3-2100 traffic controller. This paper was intended to report the evaluation results of two types of exit phase control — (i) fixed exit phase control and (ii) dynamic exit phase control during EVP operations. The evaluation was conducted using a HILS on an urban corridor including four coordinated-actuated signals along Lee Jackson Memorial Highway in Chantilly, Virginia. The evaluation results indicated that (i) the use of fixed exit phase control should be considered in the development of EVP strategies as it is able to minimize disruptions due to the EVP operation, and (ii) the dynamic exit phase control is capable to give an additional benefit during EVP operations. In the evaluation, the fixed and dynamic exit phase control reduced network-wide average delay time in seconds per vehicle to 2.8% and 4.5% over no exit phase control case, respectively.