Traffic Signal Retiming to Improve Corridor Performance

Abstract

Traffic signal retiming involves periodically updating existing signal coordination plans of signalized corridors. Nevertheless, there are still several limitations with the current signal retiming practice, such as managing a large set of signal coordination data, optimizing coordination parameters, diagnosing timing errors, and assessing signal coordination performance. To fill these gaps, this research introduces a novel signal retiming approach that offers transportation engineers an alternative way to assess and improve the operation of existing coordinated corridors. It allows for displaying the vehicle trajectories in the time-space diagram (TSD), based on which, transportation engineers could diagnose the potential issues with a signal coordination plan and develop an optimized signal coordination plan for the corridor. In addition, a unique signal performance index (SPI), which took into account average travel speed, number of stops, cycle length, and segment length adjustments, was developed to grade the performance of a signal coordination plan. A total of 38 signal coordination plans were applied on 8 signalized corridors in the City of Reno, Nevada, based on the proposed signal retiming approach. Through a before and after study, this research concluded that traffic signal retiming considerably improved the travel speed of the corridors and reduced delay for coordinated movements at signals. An SPI level of 76% of the retimed signal coordination plans was increased, and 16% of the retimed plans witnessed increases in either speed score or stop score. These case studies support that the proposed signal retiming approach is applicable for field practices.