Scalability in heterogeneous vehicle platoons

It is known that vehicle platoons exhibit string instability when each vehicle tries to maintain a fixed distance from its predecessor. This can be avoided if sufficiently strong coupling with the leader is employed. If instead each vehicle tracks the average distance form its neighbours, the interconnection can still be ill-conditioned in the sense that the response to disturbances is not uniformly bounded with the size of the platoon. We show in the paper that in a symmetric bidirectional scheme, arbitrarily weak coupling with the leader can make the platoon scalable. In addition, we show that despite the additional feedback in a bidirectional control law, the symmetry of the information flow enables the derivation of local conditions which, if satisfied, guarantee that an arbitrarily long heterogeneous interconnection is robustly stable.