FairLight: Fairness-Aware Autonomous Traffic Signal Control With Hierarchical Action Space

Abstract

Although Reinforcement Learning (RL) approaches are promising in autonomous Traffic Signal Control (TSC), they often suffer from the unfairness problem that causes extremely long waiting time at intersections for partial vehicles. This is mainly because traditional RL methods focus on optimizing the overall traffic performance, while the fairness of individual vehicles is neglected. To address this problem, we propose a novel RL-based method named FairLight for the fair and efficient control of traffic with variable phase duration. Inspired by the concept of User Satisfaction Index (USI) proposed in the transportation field, we introduce a fairness index in the design of key RL elements, which specially considers the travel quality (e.g., fairness). Based on our proposed hierarchical action space method, FairLight can accurately allocate the duration of traffic lights for selected phases. Experimental results obtained from various well-known traffic benchmarks show that, compared with state-of-the-art RL-based TSC methods, FairLight can not only achieve better fairness performance, but also improve the control quality from the perspectives of the average travel time of vehicles and RL convergence speed.