Capacity improvement for mixed traffic flow by installing vehicle-to-vehicle devices on partial human-driven vehicles to serve connected automated vehicles

Vehicle-to-vehicle (V2V) communication technology in connected automated vehicles (CAVs) substantially improves traffic capacity. During initial CAV deployment phases, mixed traffic flow combining CAVs and human-driven vehicles (HVs) will inevitably co-exist on highways. The absence of V2V capabilities in HVs prevents them from providing V2V services to CAVs, thereby constraining CAVs’ capacity improvement in mixed traffic environments. To address this limitation, we propose equipping partial HVs with V2V communication devices, enabling these retrofitted HVs to transmit V2V information and create essential communication environment for CAVs. This study develops a mixed traffic capacity analysis framework that simultaneously incorporates CAV penetration rate and V2V installation rate of HVs, which aims to improve mixed traffic capacity by adjusting the V2V installation rate of HVs. Firstly, we classified car-following patterns within mixed traffic flow and calculate their probabilities. Secondly, a mixed traffic capacity model was constructed using fundamental diagram theory. Using the established model, critical values for V2V installation rate of HVs were analytically derived to achieve capacity improvements under varying CAV penetration rates. Finally, numerical experiments validated both the model’s reliability and theoretical derivations. Results demonstrate that the proposed model effectively quantifies how CAV penetration rate and V2V installation rate of HVs jointly influence mixed traffic capacity. Strategic adjustment of V2V installation rate of HVs based on each level of CAV penetration rates significantly enhances mixed traffic capacity.