How fast is still safe for truck platoons?

Truck platoons improve freight efficiency, but their high-speed safety under varying road conditions remains unclear. This study investigates the maximum safe speed of platoons by considering tire force saturation and longitudinal‒lateral coupling. A hierarchical cooperative control framework is proposed, including cooperative control, control allocation, and action execution. A five-degree-of-freedom platoon model with lane-keeping is developed, and a distributed coupled sliding mode controller computes the desired tire forces. Feasible forces are obtained through constrained optimisation within tire limits, while steering angles and torques are derived from an inverse magic formula model. Finite-time convergence and string stability are theoretically guaranteed. Matlab/Simulink–TruckSim co-simulations show the proposed scheme improves platoon safety compared with decoupled methods. Furthermore, the maximum safe speed is quantified under different adhesion and curvature conditions. The results provide insights into the safe operating envelope of platoons and support their integration into intelligent transport systems.