A Comparision of Spacing and Headway Control Laws for Automatically Controlled Vehicles¹

TLDR

The study compares constant spacing and constant headway control policies for automated vehicles. This paper investigates two longitudinal control policies for automatically controlled vehicles. The authors design string‑stable controllers by introducing a measure of string stability and presenting a systematic method for constant‑spacing control. The constant‑headway policy achieves string stability without inter‑vehicle communication, enabling mixed automated‑nonautomated systems, and its control torques are inversely proportional to headway time.

Abstract

SUMMARY This paper investigates two different longitudinal control policies for automatically controlled vehicles. One is based on maintaining a constant spacing between the vehicles while the other is based upon maintaining a constant headway (or time) between successive vehicles. To avoid collisions in the platoon, controllers have to be designed to ensure string stability, i.e the spacing errors should not get amplified as they propagate upstream from vehicle to vehicle. A measure of string stability is introduced and a systematic method of designing constant spacing controllers which guarantee string stability is presented. The constant headway policy does not require inter-vehicle communication to assure string stablity. Also, since inter-vehicle communication is not required it can be used in systems with mixed automated-nonautomated vehicles, e.g for AICC (Autonomous Intelligent Cruise Control). It is shown in this paper that for all the autonomous headway control laws, the desired control torques are inversely proportional to the headway time.