Phase-free traffic signal control for balanced flow in sensor-limited environments

This paper introduces a phase-free traffic signal control system designed to improve both efficiency and equity in sensor-limited environments. While traditional Adaptive Traffic Signal Control (ATSC) effectively reduces delays, it often results in inequitable green time allocation, particularly under oversaturated conditions. To address this issue, this study proposes a Cell Transmission Model (CTM)-based approach for estimating queue lengths beyond the detection zones of point sensors in congested conditions. By exchanging traffic information between adjacent intersections in distributed environments, the proposed approach estimates real-time queue lengths and waiting times for each traffic movement. The phase-free system dynamically allocates green time to balance these estimates, ensuring more equitable and efficient traffic management. The system was evaluated through numerical experiments on a two-intersection network and a 3 × 3 grid network, where it achieved a 15% reduction in average control delay and small deviations in the level of service between movements compared to traditional control systems. The results demonstrate the system's potential for real-world applications, particularly in urban areas with uneven traffic flows and limited sensor coverage. By addressing the dual objectives of maximizing throughput and ensuring equitable treatment of all traffic movements, the proposed control system provides a scalable solution for modern urban traffic networks.