Traffic flow stability induced by constant time headway policy for adaptive cruise control (ACC) vehicles

This paper is concerned with the traffic flow stability/instability induced by a particular Adaptive Cruise Control policy, known as the 'constant time headway policy'. The control policy is analyzed for a circular highway using three different traffic models, namely a microscopic model, a spatially discrete model, and a spatially continuous model. It is shown that the traffic dynamics will not be qualitatively consistent across the three modeling paradigms if a consistent biasing strategy is not used to adapt the constant time headway policy. The biasing strategy determines whether the feedback quantity for use in the control, is taken colocatedly, downstream or upstream to the vehicle/section/highway location. For ACC vehicles equipped with forward looking sensors, the downstream biasing strategy should be used. In this case, the constant time headway policy induces exponentially stable traffic flow on a circular highway in all three modeling frameworks.