Comparative analysis of different spacing policies for longitudinal control in vehicle platooning

Most existing automated driving vehicles in the platoon equipped with an Adaptive Cruise Control (ACC) systems and a Cooperative Adaptive Cruise Control (CACC) systems have mainly focused on enhancing safety, improving traffic efficiency problems, and reducing workload. The spacing strategy is the core of all platoon designs, and the performance of an ACC/CACC systems hinges on the select of the spacing strategy. Although, in the literature, there are many papers dealing with platoon control, detailed explanations of the operating mechanisms of two types of spacing policies including the Headway Spacing Strategy (CTHS), and Constant Spacing Strategy (CSS), and comparative studies on them are still lacking. This work presents the studies of the longitudinal control strategy of a platoon of vehicles equipped with the existing ACC systems and CACC systems under two different spacing policies to evaluate the performances. The contributions in this work are carefully reviewed and the operating mechanisms and characteristics of two different spacing policies: the CTHS and CSS, the general evaluation criteria for spacing strategies are provided and their advantages and disadvantages are based on the numerical results. Both numerical simulations and experiments with a platoon of smart cars in real-time have demonstrated the effectiveness and practicability of the presented methodology.