  In this paper, we investigate the benefits of Vehicle-to-Vehicle (V2V)
communication for autonomous vehicles and provide results on how V2V
information helps reduce employable time headway in the presence of parasitic
lags. For a string of vehicles adopting a Constant Time Headway Policy (CTHP)
and availing the on-board information of predecessor's vehicle position and
velocity, the minimum employable time headway ($h_{\min}$) must be lower
bounded by $2\tau_0$ for string stability, where $\tau_0$ is the maximum
parasitic actuation lag. In this paper, we quantify the benefits of using V2V
communication in terms of a reduction in the employable time headway: (1) If
the position and velocity information of $r$ immediately preceding vehicles is
used, then $h_{\min}$ can be reduced to ${4\tau_0}/{(1+r)}$; (2) furthermore,
if the acceleration of `$r$' immediately preceding vehicles is used, then
$h_{\min}$ can be reduced to ${2\tau_0}/{(1+r)}$; and (3) if the position,
velocity and acceleration of the immediate and the $r$-th predecessors are
used, then $h_{\min} \ge {2\tau_0}/{(1+r)}$. Note that cases (2) and (3)
provide the same lower bound on the minimum employable time headway; however,
case (3) requires much less communicated information.
