Transition Strategies to Exit Preemption Control: State-of-the-Practice Assessment

Abstract

Preempting the normal control of a traffic signal has the potential to affect the safety and efficiency of the vehicle requesting priority and the generalpurpose traffic at the intersection. These impacts may also influence traffic flow at other intersections along a roadway or within the corridor. A state-of-the-practice assessment is provided of different transition strategies used to exit a preemption control plan and return to the coordinated operation of a signal timing plan. The reallocation of green time that results from preempting a traffic signal has the potential to affect the flow of traffic negatively. A methodology that integrates the operation of a traffic signal controller with a microscopic traffic simulation model will accurately replicate the stochastic characteristics of travel and quantify the impacts of preemption control. The time required to exit a preemption control plan will vary on the basis of the exit transition strategy selected, when this plan terminates, and where the normal signal timing plan would have been if it had not been preempted. The preemption control exit transition strategies available to practitioners are typically restricted to the options supported by different types of traffic controllers or firmware products. The five most commonly available exit transition strategies are reviewed, and additional research needed to advance the state of the practice and the state of the art in using preemption control exit transition strategies is also identified.