Shared use of dedicated lanes by connected and automated buses and private vehicles: A multi-green-wave signal control scheme

In the initial phase of implementing connected and automated vehicle (CAV) technology, the coexistence of human-driven vehicles (HVs) and CAVs is anticipated for the foreseeable future. While dedicated CAV lane is recognized as an effective solution to enhance traffic safety and efficiency in mixed traffic scenarios, it faces the challenges of road resource wastage, especially at low CAV penetration rates. Therefore, this study proposes a novel concept of a shared CAV lane for both connected and automated buses (CABs) and private CAVs, and develops a multi-green-wave control method for arterials to achieve space–time coordination in heterogeneous traffic. The two-dimensional traffic coordination aims to concurrently improve the service level of CABs and enhance overall traffic efficiency. A three-scale framework is established to integrate the control problems at the lane, intersection, and arterial levels. With the deployment of CAV lanes, lane-specified flow distribution control problem is investigated at the lane level, and a dedicated phase is designed to provide exclusive right-of-ways for CAVs, and jointed with an online conflict-free control strategy at the intersection level. Building upon this, a multiple green-wave design is developed for heterogeneous traffic at arterials, to take full exploit of the space–time resources of both CAV lanes and regular lanes and further improve traffic efficiency. To address the challenges of large-scale and complicated-structure optimization and enable real-time implementation, a hierarchical solution method is proposed. The original problem is decomposed into sub-problems, which can be efficiently solved with an approximation approach to relax the bounding constraints among them. Simulation experiments conducted on an arterial in Singapore validate the performance of the proposed methods. The results demonstrate that the proposed two-dimensional coordination strategy significantly improves traffic efficiency compared to other classic counterpart strategies, reducing the average travel delay for CABs, private CAVs, and HVs by at least 20.4%, 37.4%, and 21.4%, respectively.