Real-Time Offset Transitioning Algorithm for Coordinating Traffic Signals

Abstract

A traffic signal offset transitioning algorithm is introduced that can be viewed as an integrated optimization approach designed to work with traditional coordinated-actuated systems. The proposed approach assumes a fixed cycle length (selected by either time of day or some traffic-responsive technique). The splits are determined by each local controller subject to maximum and minimum constraints traditionally imposed by coordinated-actuated signal systems. End-of-green offsets at each intersection are continually adjusted by the proposed algorithm with the objective of providing smooth progression of a platoon through an intersection using the volume and occupancy profile of advance detectors. The algorithm was implemented in a hardware-in-the-loop simulation and evaluated with a set of National Transportation Communications for Intelligent Transportation Systems Protocol (NTCIP) National Electrical Manufacturers Association controllers. The offsets were manipulated with NTCIP messages. The unique aspect of this algorithm is the cycle-based procedure used to tabulate volume and occupancy profiles, which can then be used to adjust the offsets in a traditional coordinated-actuated signal system. This automatic tuning process is analogous to an engineer or technician standing beside the cabinet and tuning the offset so that the coordinated phase turns green at the appropriate time to facilitate smooth progression of the upstream platoon. Because only the offsets are tuned, it is unlikely that this algorithm will be able to achieve the global optimum parameters or rapid adaptation possible with model-based approaches; nevertheless, this algorithm has the advantage of working within the framework of traditional coordinated-actuated signal systems that are familiar to system operators.