Braking in Close Following Platoons: The Law of the Weakest

This paper is concerned with the realization of semi-autonomous vehicle arrangements as the natural transition towards fully automated traffic. In particular, we are interested in road trains or platoons, which involve a group of vehicles at close following distances. This is known to reduce fuel -- or energy -- consumption due to reduced aerodynamic forces acting on them. Currently, available techniques and technologies allow for inter-vehicle distances close to 5 meters with suboptimal fuel/energy savings. To obtain the most savings from a platoon formation (with even less consumption for the lead vehicle), it has been shown that the inter-vehicle distance needs to be reduced to 2.5 meters or less making braking maneuvers even more dangerous. In this paper, we present the design and analysis of a brake-by-wire system for the above case, whose operation is characterized by the law of the weakest. That is, the system automatically adapts braking forces at different platoon members -- taking vehicles' load condition, etc. into account -- to equalize that of the weakest one, i.e., the one braking at the slowest rate in the platoon. We present simulation results based on an automotive hardware-in-the-loop (HiL) setup with realistic car models. Our experiments shows that the proposed system is safe, enabling for collision-free emergency braking at intervehicle distances of 2.5 meters and, hence, paving the way for highly efficient platoons.