Relation Among Average Speed, Flow, and Density and Analogous Relation Between Density and Occupancy

Abstract

To counter the growing body of literature disputing that average vehicle speed is the ratio of flow to density, the relation is shown to hold as an identity when the variables are defined in the manner described by Edie. In similar fashion, the analogous relation between density and occupancy is shown to be true. These identities are illustrated with data measured by paired loop detectors, which underscores that Edie’s definitions are natural ways to treat the variables. The detector data are further used to show that any disputes surrounding the validity of these identities are largely the result of having defined (i.e., measured) the traffic variables in some other ways.