  This paper is concerned with the study of bidirectionally coupled platoon
systems. The case considered is when the vehicles are heterogeneous and the
coupling can be nonlinear and asymmetric. For such systems, a sufficient
condition for $\mathcal{L}_{\infty}$ string stability is presented. The
effectiveness of our approach is illustrated via a numerical example, where it
is shown how our result can be recast as an optimization problem, allowing to
design the control protocol for each vehicle independently on the other
vehicles and hence leading to a bottom-up approach for the design of string
stable systems able to track a time-varying reference speed.
