  This paper revisits the robustness analysis and distributed ${ H}_\infty$
controller design for the platooning of connected vehicles. Recently, the
relevant result subjected to the undirected topology has been studied, in the
light of the symmetry of Laplace matrix. It is well known that the same problem
is more challenging for the \emph{directed} topology, since the Laplace matrix
ceases to be symmetric. In this paper, the problem is solved by introducing
more weighting parameters and setting suitable values for them. Then we show
that the introduced weighting parameters lead to a positive effect on
robustness, and solve the problem of feedback high gain. Finally, two numerical
simulations and a practical simulation based on Next Generation Simulation
(NGSIM) dataset are used to illustrate the effectiveness of our method.
