Signal-free Intersection Cooperative Optimization Scheme for CAVs with Velocity-prioritized Emergency Vehicles

This paper studies cooperative trajectory planning for multiple connected and automated vehicles (CAVs) traveling from and off multi-lane roads at a signal-free intersection with the consideration of velocity-prioritized emergency vehicles, such as ambulances and fire engines. In most of the current studies, the trajectory of each CAV is either fixed or in line with the topology of the fleet, whilst the velocity of each CAV is preset with an inflexible pattern, which severely limits the efficiency of the collaboration. Moreover, the priority of emergency vehicles is not well considered in the aforementioned strategies. This research is aimed to address the issues. The intersection control task is formulated as an optimal control problem (OCP), in which the velocities of the CAVs can be set with any reasonable aspiration, while there is no lane discipline at the intersection. When designing the control strategy, unmanned vehicles of various sizes with differentiated velocity priorities are taken into account. An adaptive stepwise optimization (ASO) method is proposed to improve the OCP solution efficiency.