An experimental comparative study of autonomous and co-operative vehicle-follower control systems

This paper is a comparative study of the performance of constant-time-gap a utonomous control systems and co-operative longitudinal control systems tha t use inter-vehicle communication. Analytical results show that the minimum time gap that can be achieved in autonomous control is limited by the band width of the internal dynamics of the vehicle. Experimental results from ty pical sensors and actuators are used to show that in practice it is very di fficult to achieve a time gap less than 1 s with autonomous vehicle followi ng. This translates to an inter-vehicle spacing of 30 m at highway speeds a nd a theoretical maximum traffic flow of about 3000 vehicles per hour. The quality of radar range and range rate measurements pose limitations on the spacing accuracy and ride quality that can be achieved in autonomous contro l. Dramatic improvements in the trade-off between ride quality and spacing accuracy can be obtained merely by replacing radar range rate in the autono mous control algorithm with the difference between the measured velocities of the two cars (a rudimentary form of co-operation). As a baseline compari son, the experimental performance of fully co-operative control is presente d. An inter-vehicle spacing of 6.5 m is maintained in a platoon of 8 co-ope rative vehicles with an excellent ride quality and an accuracy of +/-20 cm. Extending this to a 10-vehicle platoon makes it possible to achieve theore tical maximum traffic flows of about 6400 vehicles per hour. Another issue of importance addressed in the paper is the need to accommoda te malfunctions in radar (ranging sensor) measurements. Measurement errors can occur due to hardware malfunctions as well as due to road curves, grade s and the highway environment in the case of large inter-vehicle spacing. T he ability of a co-operative control system to monitor the health of the ra dar and correct for such errors and malfunctions is demonstrated experiment ally. (C) 2000 Elsevier Science Ltd. All rights reserved.