This paper investigates formation control protocols for autonomous vehicular strings with vehicle-to-vehicle (V2V) communication connections. To this end, a four-layer framework is first proposed to illustrate the cooperative mechanism within and across strings. Then, cooperative control protocols are designed based on vehicle role, i.e., leader or follower, in vehicular multi-string. In particular, longitudinal controllers are designed for single string and multiple strings by incorporating inter-vehicle gap and velocity difference of the follower vehicle with respect to the preceding vehicle and the lead vehicle. In addition, lateral controllers are proposed for single string and multiple strings based on the artificial function method. The proposed protocols ensure that follower vehicles asymptotically track the leader within each string, while different vehicular strings can form a desired platoon pattern. The study further analyzes the stability and consensus of the proposed control protocols using the Routh–Hurwitz stable criterion and the Lyapunov technique. Numerical experiments are performed for two cooperative mechanisms—parallel and serial. Results from numerical experiments illustrate the effects of the proposed control protocols on road throughput and demonstrate their effectiveness for position and velocity consensuses.
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