Methodology to Assess Traffic Signal Transition Strategies for Exit Preemption Control

Enabling vehicles to preempt the normal operation of traffic signals has the potential to improve the safety and efficiency of both the requesting vehicle and all other vehicles. Little is known about which strategy is the most effective to exit from preemption control and transition back to the normal traffic signal timing plan. This research evaluates the commonly available transition strategies: best-way, long, short, and hold strategies. The major contribution of this research is to enhance the methodology to evaluate the impacts of using these alternative transition strategies with the software-in-the-loop simulation tool. The research concludes that a statistically significant interaction exists between traffic volume levels and traffic signal transition strategies; this eliminates the ability to determine the isolated effects of either the transition strategies on average travel delay and average travel time or the effects of changes in traffic volume levels on average travel delay and average travel time. Conclusions, however, could be drawn on the performance of different transition strategies for specific traffic volume levels. The research also concludes that for the base traffic volume and a 40% increase in traffic volume, the most effective transition strategies are the best-way and long or hold alternatives. The best way was the most effective transition strategy for a 20% increase in traffic volume. The least effective strategy is the short transition strategy for both the base and 40% increase in traffic volume and the long and short for a 20% increase in traffic volume. Further research needs to be conducted to assess the performance of different transition strategies in returning to coordinated operation under higher levels of traffic volume with varying cycle lengths and different signal timing plans and when different roadway geometric configurations are present.