The task of traffic control for automated highway systems (AHS) is drastically different from and much more complex than its conventional counterpart. This paper proposes a conceptual framework for designing a traffic control scheme. It adopts a top-down approach to defining major design steps starting with high-level feature definition. Since all AHS control features materialize through vehicle movements and there exists an infinite number of possible vehicle movements, specifying these movements and verifying that they indeed suffice for the desired features could be extremely complicated. One approach to simplifying such tasks is to define a small number of permissible moves as ‘building blocks’ and define all permissible movements in terms of these moves. With the desired features defined, the top-down approach then identifies and defines moves and related planning and movement functions that are required for supporting the desired features. Central to traffic control is planning, including system flow planning and vehicle movement planning. The former tries to optimize the macroscopic flow of aggregate traffic in the AHS while the latter plans for the microscopic movement of individual vehicles. Making the actual movements according to the vehicle movement plans requires the most detailed data about the immediate neighborhood affecting or affected by the movements. To ensure safety, initiation/continuation/abort conditions for all permissible vehicle moves must be clearly and safely defined at this level of detail. Since vehicle movement plans are generated by various controllers in the AHS, the planned vehicle moves have the potential of conflicting and interfering with one another. Based on key attributes of a move and the concept of initiation continuation/abort conditions, the paper is 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 stage. Such interferences should be minimized for efficiency. A ‘running’ example defining the traffic control scheme of a simplified AHS operating scenario is provided for illustration.
