Variable time headway for string stability of automated heavy-duty vehicles

We present adaptive nonlinear schemes for longitudinal control of automated heavy duty vehicles. An important control objective is string stability, which ensures that errors decrease as they propagate downstream through the platoon. It is well known that string stability requires intervehicle communication if a constant spacing policy is adopted. When vehicles operate autonomously, string stability can be achieved if speed-dependent spacing with constant time headway is used. This, however, results in larger steady-state spacing, which increase the platoon length hence decreasing traffic throughput. In this paper we propose a new spacing policy in which the time headway varies linearly with the velocity error. Our simulation results demonstrate that this modification significantly reduces the transient errors and allows us to use much smaller spacing in the autonomous mode of platoon operation.