A COMPARISION OF SPACING AND HEADWAY CONTROL LAWS FOR AUTOMATICALLY CONTROLLED VEHICLES

This paper investigates two different longitudinal control policies fo r automatically controlled vehicles. One is based on maintaining a con stant spacing between the vehicles while the other is based upon maint aining a constant headway (or time) between successive vehicles. To av oid collisions in the platoon, controllers have to be designed to ensu re string stability, i.e the spacing errors should not get amplified a s 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. Th e constant headway policy does not require inter-vehicle communication to assure string stability. Also, since inter-vehicle communication i s not required it can be used in systems with mixed automated-nonautom ated vehicles, e.g for AICC (Autonomous Intelligent Cruise Control). I t is shown in this paper that for all the autonomous headway control l aws, the desired control torques are inversely proportional to the hea dway time.