A Power Law for the Duration of High-Flow States in Heterogeneous   Traffic Flows
  We study the duration of "high-flow states" in freeway traffic, defined as the time periods for which traffic flows exceed a given flow threshold. Our empirical data are surprisingly well represented by a power law. Moreover, the power law exponent is approximately 2, in dependently of the chosen flow threshold. In order to explain this discovery, we investigate a simple theoretical model of heterogeneous traffic with overtaking maneuvers, which is able to reproduce both, the empirical power law and its exponent. 
Dirk Helbing and Benno Tilch