In the third part of the state of the art report "traffic flow models" the basic diagram is discussed. It is a representation of the relation which consists in balance between intensity, density and average speed. Balance is considered in such a way that the magnitudes are constant for some time. A number of theoretical models of the basic diagram are discussed. They are based on several propositions about the behaviour of vehicle-driver combinations in the traffic flow or on an analogy between a traffic flow and a physical stream. It is shown that different starting points sometimes lead to the same basic diagram. At the end the meaning of the basic diagram for highway design and traffic quality is discussed. For abstracts of parts 1, 2 and 4, see IRRD abstracts nos 240606, 240607 and 240609.
Abstract