TRAFFIC CONTROL FOR AUTOMATED HIGHWAY SYSTEMS - A CONCEPTUAL-FRAMEWORK

The task of traffic control for automated highway systems (AHS) is dra stically different from and much more complex than its conventional co unterpart. This paper proposes a conceptual framework for designing a traffic control scheme. It adopts a top-down approach to defining majo r design steps starting with high-level feature definition. Since all AHS control features materialize through vehicle movements and there e xists an infinite number of possible vehicle movements, specifying the se movements and verifying that they indeed suffice for the desired fe atures could be extremely complicated. One approach to simplifying suc h tasks is to define a small number of permissible mores as ''building blocks'' and define all permissible movements in terms of these moves . With the desired features defined, the top-down approach then identi fies and defines moves and related planning and movement functions tha t are required for supporting the desired features. Central to traffic control is planning, including system flow planning and vehicle movem ent planning. The former tries to optimize the macroscopic flow of agg regate traffic in the AHS while the latter plans for the microscopic m ovement of individual vehicles. Making the actual movements according to the vehicle movement plans requires the most detailed data about th e immediate neighborhood affecting or affected by the movements. To en sure safety, initiation/continuation/ abort conditions for all permiss ible vehicle moves must be clearly and safely defined at this level of detail. Since vehicle movement plans are generated by various control lers in the AHS, the planned vehicle moves have the potential of confl icting and interfering with one another. Based on key attributes of a move and the concept of initiation/continuation/abort conditions, we a re able to define rigorously the concepts of conflict and interference among different moves. Such conflicts must be recognized and resolved in time for safety; they should also be prevented at the planning sta ge. Such interferences should be minimized for efficiency. A ''running '' example defining the traffic control scheme of a simplified AHS ope rating scenario is provided for illustration.