Balancing Safety and Capacity in an Adaptive Traffic Signal Control System

This research focuses on the development of a real-time signal timing methodology and algorithms that balance safety and efficiency. This research consists of two phases: Phase I was completed in December 2009; it examined the relationships between signal timing and surrogate measures of safety, namely the frequency of rear-end, angle and lane-change conflicts. The FHWA Surrogate Safety Assessment Methodology (SSAM) was used to evaluate various simulated scenarios to test the relationships between signal timing parameters such as cycle, offset, split, phase change interval, detector extension time, left-turn phase protection options and left-turn phase sequence and the occurrence of traffic conflicts. The objective of this second phase of the research project is to develop algorithms that can balance the performance of the traffic control system for both efficiency and safety and can work with both NEMA and 2070 traffic control firmware. Phase II will include the development of a multi-objective optimization methodology using the five principle algorithms that comprise the proposed adaptive system for tuning the cycle length, splits, offsets, left-turn phase protection treatment and left-turn phase sequence of a set of intersections. Phase II will define the limits for each parameter-tuning algorithm. The set of multi-algorithms that will be developed under this research will extend the parameter tuning approach that was successfully developed in the FHWA ACSLITE project. The new algorithms will provide signal timing parameter sets that improve both the safety and efficiency of the traffic system. If both objectives are not able to be satisfied, the methodology will attempt to improve efficiency as much as possible until safety is detrimentally affected to a user-specified limit.