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The maximum capacity, cost, and safety of an automated highway system are largely dependent on the selected headway policy, i.e., the specification of a minimum acceptable headway (as a function of speed) for mainline operations. Here a policy, designed to avert collisions due to "reasonable" lead-car decelerations, is presented and evaluated in the context of achieving high capacity (≥3600 vehicle/lane/hr) over a range of typical highway speeds-13.5 to 30 m/s (30.2 to 67.2 mi/h). This involved a detailed analysis to determine both the relationships between, and the requirements on, the seven parameters which are embedded in this policy. These pertain to systems-level operations, the capabilities of a vehicle's automatic control system, and the vehicle/ roadway interface. The trade-offs associated with safety, capacity, and cost (in the form of required future development efforts) are identified, and three general approaches to selecting parameters for an operational system are specified.
Date of Publication: Feb 1979