A Subplatooning Strategy for Safe Braking Maneuvers

Reducing the inter-vehicle separation in a platoon results in the most benefits in terms of aerodynamic savings and vehicles throughput. However, this makes braking maneuvers dangerous and leads to long stopping distances, in particular, when considering heterogeneous vehicles with different braking capacities. Even though control theoretic approaches exist for the platoon cruise operation, the scenario of sudden braking has to be designed separately as the system reaches saturation, i.e., in order to minimize the stopping distance of the platoon, the application of the maximum possible braking forces is required. This cannot be handled by standard control systems alone, since they rely on varying (control) variables/signals, which is not possible under saturation. In this paper, we are concerned with vehicles of heterogeneous braking capacity and propose a subplatooning strategy that not only guarantees a collision-free braking, but also minimizes the stopping distance. Vehicles within each subplatoon have inter-vehicle separations of below one car length, whereas the inter-subplatoon separation is increased to compensate the differences in decelerations between subplatoons. We evaluate this scheme using a realistic simulation based on complex vehicle dynamics models and a HiL (hardware in the loop) setting.