Exploiting space buffers for emergency braking in highly efficient platoons

With the advent of autonomous driving, road trains or platoons are regaining importance as a meaningful way of improving traffic efficiency and economizing on fuel/energy. It has been shown that reducing inter-vehicle separations to less than one car length results in the most benefits for the whole platoon; however, this poses a number of challenges. In particular, it becomes difficult to guarantee a collision-free braking in an emergency situation considering that individual vehicles may have different braking capacities in real-life settings - due to, for example, different load conditions, etc. Although control-theoretic approaches can be used to design a platoon's cruise operation, emergency braking leads to saturation, i.e., the maximum possible braking force is applied so as to stop the platoon in the shortest possible time and needs to be designed separately. In this paper, we address this issue and introduce a cyber-physical approach that guarantees a collision-free braking in emergency situations. The proposed approach exploits space buffers contained in between vehicles and can be configured to reduce stopping distance and platoon length, while maximizing aerodynamic benefits. We evaluate our approach based on realistic simulations with vehicle dynamics models typically used in the automotive industry for hardware-in-the-loop (HiL) testing. The effects of communication loss during platoon operation are also considered and fail-safe mechanisms are proposed and investigated.