Two-stage algorithm for traffic signal optimization and web-service system development

Efficient control of traffic signals for vehicles and pedestrians at intersections is critical for relieving traffic congestion. Considering the unique characteristics of intersections, such as the number of roads, the presence or absence of crosswalks, road geometric shapes, and traffic demand patterns, an appropriate phase sequence and duration for traffic signals must be established at each intersection. This paper proposes a simulation-based two-stage algorithm comprising integer-constrained Adam (ICA) and tabu search (TS) to optimize the phase sequence and duration for arbitrary intersections with arbitrary traffic-demand patterns. The ICA promptly identifies a promising region in which a global optimal solution is likely to be obtained, whereas TS determines the best solution near the region. The performance of the proposed algorithm that optimizes phase durations with fixed phase sequence is evaluated against several baseline methods using 24 instances across six actual intersections. Experimental results show that the proposed algorithm reduces the average travel time by 20.2% compared with existing traffic signals within a computation time of 4 min, thus providing a near-optimal solution eight times faster than commonly used population-based metaheuristics. Furthermore, the algorithm demonstrates robust performance across heterogeneous vehicles and recommends the best phase sequence that effectively alleviates congestion in current traffic signal systems. The optimized phase sequence with best phase durations further reduces the average travel time by approximately 11.3% compared with the existing phase sequence with best phase durations at an actual intersection. To facilitate its widespread use, a free, open web-service system named "Smart Intersection for Traffic Efficiency" is developed, which enables users to optimize traffic signal systems without requiring optimization background or simulation knowledge. This article proposes a simulation-based two-stage algorithm consisting of the integer constrained Adam (ICA) and Tabu search (TS) for optimizing the phase sequence and phase duration for arbitrary intersections with arbitrary traffic demand patterns. The proposed algorithm is used to develop a free open web service system, named smart intersection for traffic efficiency (SITE; http://logistics.postech.ac.kr/site), which can be used for traffic signal optimization without simulation knowledge. image