Time scales, fluctuations and constant flow periods in uni-directional traffic☆

Abstract This paper presents the results of an investigation into some of the short- and long-term properties of traffic flow on a uni-directional section of freeway. The investigation was prompted by a desire to develop a test for isolating periods of constant flow. Along with a test which will yield constant flow periods and can be applied in an automatic fashion, we present: (1) a method for smoothing counts of cars, which largely eliminates local fluctuations, to observe the large time scale behavior of flow; (2) results on the independence of successive counts of cars and the theoretical structure of these counts, along with techniques for accurate estimation of the variance of counts; (3) results on the dependency between counts in adjacent lanes; (4) a discussion of the variance-to-mean ratio and its utility in understanding traffic flow; and (5) results on estimation of the variance of counts using the moments of the time headway distribution.