Traffic Flow Theory: Historical Research Perspectives

Traffic flow is a kind of many-body system of strongly interacting vehicles. Traffic jams are a typical signature of the complex behavior of vehicular traffic. Various mathematical models are presented to understand the rich variety of physical phenomena exhibited by traffic. This paper provides an overview of what is currently the state-of-the-art with respect to traffic flow theory. Starting with a brief history about vehicular traffic flows, it discusses the Greenshields, Greenberg’s, Gurein’s, etc., models. This paper also discusses some basic relations between traffic flow characteristics, i.e., the fundamental diagrams; speed, volume, and density relationships; hydrodynamic analogies; and traffic hump formation (shock wave), and sheds some light on the different points of view adopted by the traffic engineering community. Moving on, it reviews some performance indicators that allow one to assess the quality of traffic operations. A final part of this paper gives the probabilistic description of traffic flow, distribution of vehicles on a road.