Maximizing diverging area flow in mixed traffic: Selection of CAV dedicated lane configuration via an enhanced cell transmission model

Establishing dedicated lanes for connected and automated vehicles (CAV-DLs) can mitigate the adverse impacts of interactions between human-driven vehicles (HVs) and CAVs on traffic operations, thereby improving efficiency. Existing CAV-DL schemes primarily focus on enhancing the throughput of basic freeway segments. They often neglect critical bottleneck areas, such as diverging areas. Furthermore, prevailing research methods struggle to balance modeling accuracy with computational efficiency. To address these issues, this paper proposes an enhanced Cell Transmission Model (CTM) to develop CAV-DL configuration schemes aimed at increasing the throughput of diverging areas. The model introduces Mainline-bound Virtual Cells to store through and free lane-changing vehicles, and Off-ramp-bound Virtual Cells to store mandatory lane-changing vehicles. To better reflect how lane-changing behaviors in diverging areas affect cellular traffic flow parameters, this model establishes two probability models. First, it accounts for the impact of lane saturation on lane-changing utility to establish a free lane-changing probability model. Second, it considers the effect of the vehicle's distance to the diversion endpoint’s on lane-changing pressure to develop a mandatory lane-changing probability model. Taking into account the differentiated access restrictions imposed by CAV-DLs on HVs in the two types of virtual cells, traffic flow transfer rules for mixed traffic in diverging areas are formulated. Simulation experiments conducted on a one-way three-lane freeway diverging area show that: (1) not deploying any dedicated lane is optimal when the CAV market penetration rate (MPR) is 0.1 or 0.9; (2) deploying dedicated lanes can significantly improve diverging area efficiency when 0.3 ≤ MPR ≤ 0.7; (3) among configurations with CAV-DLs, the scheme placing one CAV-DL in the outermost lane (MMC) exhibits the broadest applicability. In contrast, the applicability of the scheme with two CAV-DLs in the two outermost lanes (MCC), as well as the scheme with CAV-DLs on the innermost and outermost lanes (CMC), is highly correlated with diverging intensity. This research provides technical support for lane-level simulation of diverging area operations and offers a reference for formulating CAV-DL schemes on highways with mixed traffic flow.