A quasi-dynamic robust control scheme for signalized intersections

Conventional vehicle-actuated traffic signal control attempts to achieve system optimum by ending a phase as soon as queues served during that phase vanish. In this article, the authors extend this logic to intersections where a stable cycle length is desirable (e.g., for signal coordination or other considerations). The proposed control scheme dynamically updates green allocation to keep queues on all approaches well balanced. Different from fully dynamic control strategies, the proposed quasi-dynamic scheme is based on a finite set of fixed timing plans with a common cycle length. The decision of switching from one plan to another is made at the beginning of each cycle based on the queue state in the previous cycle. Our experimental results showed that the performance of the proposed scheme is robust with respect to random fluctuation, systematic changes in demand, and input data quality. Although the proposed scheme does not attempt to minimize total system delay directly, it provides a good solution for reducing total system delay compared with the signal timing plan optimized for system delay. The preservation of a stable cycle length in the proposed signal timing plan has made it possible to incorporate the proposed scheme into the development of control strategies for an arterial where signal coordination is essential to the performance of the system.