A theory of traffic flow in automated highway systems

This paper presents a theory for automated traffic flow, based on an abstraction of vehicle activities like entry, exit and cruising, derived from a vehicle’s automatic control laws. An activity is represented in the flow model by the space and time occupied by a vehicle engaged in that activity. The theory formulates Traffic Management Center (TMC) plans as the specification of the activities and velocity of vehicles, and the entry and exit flows for each highway section. The authors show that flows that achieve capacity can be realized by stationary plans that also minimize travel time. These optimum plans can be calculated by solving a linear programming problem. The theory permits the study of transient phenomena such as congestion, and TMS feedback traffic rules designed to deal with transients. The authors propose a ‘greedy’ TMC rule that always achieves capacity but does not minimize travel time. They undertake a microscopic study of the ‘entry’ activity, and show how lack of coordination between entering vehicles and vehicles on the main line disrupts traffic flow and increases travel time. The authors conclude by giving some practical indication of how to obtain the space and time usage of activities from vehicle control laws. Finally, they illustrate the concepts presented in this paper with two examples of how the model is used to calculate the capacities of a one-lane automated highway system. In one example the authors study market penetration of adaptive cruise control and in the second example they study the effect of platooning maneuvers in a platooning architecture for AHS.