Vehicle merging control design for an automated highway system

The merging process in an Automated Highway System (AHS) is divided into a speed adjustment stage and a lane merging stage. Three important parameters, namely, acceptability, availability and pursuability, are analyzed to characterize the AHS lane gap features for the ideal, smooth and safe merging of the ramp vehicles. Three control guidance laws, namely, linear, optimal and parabolic speed profiles, are developed to describe the desired behaviors of the merging vehicle based on the merging quality and safety. The desired states of the merging vehicle are generated through the outer loop by specified control guidance law. The tracking errors compared with desired states are eliminated by the proper design of controllers in the inner loop. Both longitudinal and lateral controllers are designed using sliding mode control theory that can handle the nonlinear and model uncertainties of the vehicle dynamics. The simulation results show encouraging results. INTRODUCTION There has been good deal of research in the area of AHS recently, such as Compendium of Research Summaries (1 994). The merging control is an important AHS operation. Hence, its study and control design is very important. The subject of merging control under manual driving has been studied extensively by many traffic engineers in 1960s, Drew,(1968), Drew, et. al. (1965). Yang and Kurami (1993-a) proposed an automated merging system for potential application to ITS (Intelligent Transportation Systems). Yang & Kurami (1 993-b) also proposed another merging control system that guides and controls the longitudinal motion of the merging vehicle to reach the target gap at the merging point. Kachroo (1 993) applied the sliding mode control method to the vehicle longitudinal headway control. Hedrick, et. al. (1991) described a combined throttle/brake control algorithm designed to control vehicle space headway within a fully automated “platoon” vehicles. Peng and Tomizuka (1993) developed a lateral control system for vehicle lane keeping maneuver. The problem statement for the control design is given as follows: Given an acceptable gap G formed by the highway lane contiguous with the ramp, with the speed V, and upstream distance D, to the merging point 0 in the highway lane at time t,,, a ramp merging vehicle M with current initial position x, and speed V,, is to be driven safely, smoothly and eflciently under automatic control to the equivalent target position S with the gap speed V, , in the estimated gap traveling time period T = t,-t,,. Meanwhile the vehicle is continuously steered to stay in the center o j the lane.