Fundamental diagram of mixed traffic flow considering dedicated and shared lanes management policies for CAVs

To investigate how setting up connected and automated vehicles (CAVs) dedicated lanes can maximize the traffic capacity, this paper proposes a fundamental diagram of mixed traffic flow with CAVs dedicated lanes, in which CAVs dedicated lanes only allow CAVs and shared lanes allow both CAVs and human-driven vehicles (HDVs). Firstly, for CAVs overflowing and not overflowing, the car-following modes and their proportion in CAVs dedicated lanes and shared lanes are analyzed, respectively. Secondly, based on steady-state conditions and average time headway, the fundamental diagram of mixed traffic flow with and without CAVs dedicated lanes is derived. Then, the relevant properties of the fundamental diagram with CAVs dedicated lanes are proposed and proved. Finally, multiple parameters, such as the overflow ratio of CAVs, the penetration rate of CAVs, and the number of CAVs dedicated lanes, are adopted to discuss their impact on the fundamental diagram. Results show that (1) one and two CAVs dedicated lanes of three manual lanes can maximize the traffic capacity when the penetration rate of CAVs reaches 0.16 and 0.31, respectively; (2) compared with C-H policy, C-S policy can maximize the traffic capacity when the penetration rate of CAVs reaches 0.45 with one CAVs dedicated lane and 0.73 with two CAVs dedicated lanes; (3) the traffic capacity of C-S policy is up to 1.3 times and 1.6 times that of mixed traffic flow with one and two CAVs dedicated lanes of three manual lanes, respectively. This work provides insights into the impact of CAVs dedicated lanes on traffic systems and helps decide the optimal number of dedicated lanes.