Integrated Longitudinal and Lateral Hierarchical Control of Cooperative Merging of Connected and Automated Vehicles at On-Ramps

Connected and automated vehicles (CAVs) can improve traffic safety and transportation network efficiency while also reducing environmental impacts. However, congestion and accidents can easily occur at merging roadways. Therefore, coordinating cooperative merging of CAVs is one of the most common traffic management problems. This paper addresses the problem of integrated longitudinal and lateral cooperative merging control with practical implications for CAVs approaching on-ramps. A hierarchical and decentralized cooperative coordination framework was developed to systematically control the merging of CAVs. The control system of each vehicle can be divided into an upper-level and lower-level. For upper-level control, an optimal control-based algorithm considering input constraints was presented to optimize fuel consumption and passenger comfort. A decision strategy was developed to optimize the start time of lateral trajectory planning. To achieve lower-level control, a Proportional-Integral (PI) controller was used for tracking the optimized longitudinal speed of the upper-level and a decentralized unified algorithm based on nonlinear model predictive control was proposed for tracking the upper-level optimal trajectory. To avoid lateral collision, the driving safety field based on vehicle size and motion state was selected as one of tracking the optimization objectives. Efficiency of the proposed framework and the algorithm was validated by CarSim/Simulink co-simulations of near-real-world vehicle scenarios. The proposed integrated merging control system can improve traffic efficiency and reduce fuel consumption compared to baseline with the potential for real-world application. Furthermore, the results demonstrate the potential applicability of cooperative control methods based on upper-level vehicle control.