Safe and Stable Connected Cruise Control for Connected Automated Vehicles with Response Lag

Controlling connected automated vehicles (CAVs) via vehicle-to-everything (V2X) connectivity holds significant promise for improving fuel economy and traffic efficiency. However, to deploy CAVs and reap their benefits, their controllers must guarantee their safety. In this paper, we apply control barrier function (CBF) theory to investigate the safety of CAVs implementing connected cruise control (CCC). Specifically, we study how stability, connection architecture, and the CAV's response time impact the safety of CCC. Through safety and stability analyses, we derive stable and safe choices of control gains, and show that safe CAV operation requires plant and head-to-tail string stability in most cases. Furthermore, the reaction time of vehicles, which is represented as a first-order lag, has a detrimental effect on safety. We determine the critical value of this lag, above which safe CCC gains do not exist. To guarantee safety even with lag while preserving the benefits of CCC, we synthesize safety-critical CCC using CBFs. With the proposed safety-critical CCC, the CAV can leverage information from connected vehicles farther ahead to improve its safety. We evaluate this controller by numerical simulation using real traffic data.