Adaptive control in transportation

A transportation control system maintains the flow of traffic according to a schedule by implementing various policies (e.g. procedures, rules, priorities, etc.). In a conventional control system the schedule is fixed and the policies are deterministic. An adaptive control system, on the other hand, has an internal mechanism for altering its policies which, in turn, adjust the schedule in response to demand and system status. An adaptive control system combines five basic functions: (1) surveillance, to detect traffic; (2) communications, to relay surveillance data and control signals; (3) performance evaluation, to compare the difference between the desired and current operation; (4) on-line data processing, to determine the control signals and scheduling; and (5) overall system operation, i.e., the functional summation of (1), (2), (3) and (4). An ultimate system would also generate predictions of future demand which would be factored into the control adaptation process. This paper summarizes recent progress in the implementation of adaptive control systems in transportation. The applications discussed include control of freeway ramps, urban street traffic, air traffic, and urban rapid transit.