Stability of String of Adaptive Cruise Control Vehicles with Parasitic Delays and Lags

In this paper, we examine the effect of parasitic delays and lags on the stability of a string of vehicles equipped with adaptive cruise control (ACC) system which is employed a constant time headway (CTH) policy. The control law of the ACC system is based on a simpler model of the vehicle that does not ignore the parasitic delays and lags. The main result of this paper is that string stability can be guaranteed if the constant time headway h, is at least twice the sum of the parasitic delays Delta, and the parasitic lags tau, that is, h > 2 (Delta+tau). This result extends and generalizes the earlier results of Darbha by considering parasitic delays and lags and provides a practical direction for ACC system design and implementation from the viewpoint of robustness to parasitic delays and lags.