Flexible Traffic Signal Control Method Based on Non-conflict Merging Strategy

The development of intelligent and connected vehicles makes it possible to finely control the vehicle trajectories and the new ideas and concepts have appeared for urban traffic signal control. This paper proposes a flexible signal control method based on non-conflict merging strategies. The merging phase is introduced to accommodate both through and left-turn vehicles. Based on the NEMA (National Electrical Manufacturers Association) dual-ring phase structure, the merging strategy is integrated to form a dual-ring merging signal phase structure with 12 action spaces. With the optimized phase structure, this paper proposes an improved reinforcement learning algorithm for the signal timing. The algorithm fully considers the actual rules of phase switching under the NEMAdual-ring structure and learns the optimal phase control strategy for the current state. The performance of the proposed control method is tested with the SUMO simulation. Different control strategies are compared, including the traditional NEMA dual-ring structure, and the NEMA dual-ring merging phase structure under both actuated control and improved reinforcement learning algorithms. The impact of the penetration rate of connected vehicles on the control performance is also analyzed. The results show that the proposed method can generate more realistic and flexible phase timing plans while maintaining the NEMA dual-ring merging phase structure. Under different traffic flow conditions, especially high traffic volume and uneven distribution of traffic volume scenarios, compared with the traditional NEMA dual-ring phase structures and actuated control methods, the proposed method can reduce vehicle delay by about 37% and hence improve the traffic operation at the signalized intersections.