Cooperative control of mixed CAV-HDV platoons with hierarchical optimization for oscillation mitigation

The integration of Connected and Automated Vehicles (CAVs) and Human-Driven Vehicles (HDVs) in mixed traffic environments introduces significant challenges to traffic stability. In particular, disparities in dynamic responses between CAVs and HDVs often lead to the propagation and amplification of speed disturbances, exacerbating traffic oscillations. To address this issue, a Hierarchical Optimization-based Hybrid Fleet Cooperative Control (HO-HFCC) model is proposed, incorporating a novel Leader-Following (LF) communication topology. To tailor control strategies to vehicle types, the HO-HFCC model adopts a two-layer architecture: an Oscillation-Optimized Feedforward Control (OOFC) for CAVs, integrating the leading vehicle information and performing nonlinear dynamic adjustment of inter-vehicle spacing to actively suppress the longitudinal propagation of speed fluctuations; and a Speed-Perception-Enhanced Control (SPEC) for HDVs, enhancing response accuracy via multi-source feedback to mitigate oscillation amplification caused by delays. Simulations show that, compared with the reference strategy, the HO-HFCC model reduces CAV speed fluctuations by 10.5 % and HDV speed differences by 50.2 %, effectively accelerates formation convergence, and suppresses oscillations to a greater extent as the CAV penetration rate increases. Additionally, strategy-level simulations demonstrate improvements in safety, platoon stability, and energy efficiency, confirming the superior performance of the HO-HFCC model across multiple objectives. This study provides a detailed and scalable solution for suppressing traffic oscillations in real-world mixed platoon scenarios.