Mitigating oscillations of mixed traffic flows at a signalized intersection: A multiagent trajectory optimization approach based on oscillation prediction

To mitigate the traffic oscillations generated when traffic flow encounters a red light at a signalized intersection, many studies have used reinforcement learning to control connected and automated vehicles (CAVs) trajectories to avoid oscillations. These methods, which are effective in mitigating oscillations in a pure CAV environment, perform poorly when applied to mixed traffic streams, due to the fact that most of the methods ignore that human vehicles (HVs) in mixed traffic flows stop at red lights and trigger oscillations, resulting in significant “trajectory fluctuation” phenomena in some CAVs, which will lead to poor effectiveness in mitigating oscillations.To address this problem, We propose a method that combines oscillation prediction and multiagent trajectory optimization to mitigate the oscillations generated by HVs. First, we predict the oscillation caused by HVs stopping during a red light, and after that, we use the Newell model to predict the propagation range of the oscillation. According to whether the HV ahead produces oscillation or not, we classify CAVs into two types of agents and design the control scheme separately. The first type of CAVs are immediately adjacent to the oscillation, and we use a jam-absorption driving (JAD) strategy to treat them as absorbing vehicles to absorb the oscillation. While the second type of CAVs are vehicles other than the first type of CAVs, we use the deep reinforcement learning (DRL) method to control them to arrive at the intersection within the predicted green light time. We tested the method in a mixed traffic flow simulation environment. Experimental results show that this method can effectively suppress the phenomenon of “trajectory fluctuations” under different CAV penetration rates, achieving the goal of effectively mitigating oscillations thus significantly improving traffic efficiency and reducing vehicle fuel consumption. Meanwhile, the method also has the advantages of fast convergence during training and high stability during testing compared with traditional reinforcement learning methods.