Abstract
A general flow diagram is put forward. It envisages traffic flow being subdivided into three separate zones- a zone of normal flow, a zone of unstable flow, and a zone of forced flow- each zone being specified in terms of probabilities. The diagram is consistent with limited observed data, and it seems to describe traffic flow more completely than do existing models. The paper indicates generally the lines along which this flow diagram eventually might be applied in the evaluation of the quality of traffic flow, and in traffic control.