Traffic Flow Prospectives: From Fundamental Diagram to Energy Balance

Congestion modeling is a topic under consideration in traffic flow theory since Greenshields' study of traffic capacity in 1934. There are several levels of investigation dealing with different categories. Microscopic car-following dynamics, mesoscopic stochastic theories of car cluster formation as well as macroscopic fluid-dynamical models study traffic states characteristics, given by speed, flow and density, shown in the fundamental diagram. By this relationship speed and flow can be represented as a function of density, usually as a steady state dependence, but also as function of time since traffic states change continuously. Distinguishing a collection of similar traffic states as phases, the phenomenon of phase transition from (nearly) free flow to stop-and-go traffic is the emergence of a random fluctuation (e.g., of speed) developing into a vehicular congestion known as breakdown. Usually a traffic breakdown is defined as a speed drop of a certain amount within a dense traffic situation. It has always a reason but the reason is hard to analyze. To describe these dynamics successfully a probabilistic model is chosen where the unpredictable influences are summarized by a stochastic force creating vehicular platoons (called vehicular clusters) out of the metastable free flow. This spontaneous formation of a new traffic phase is modeled as a stochastic cluster emergence process. A car cluster being a vehicular platoon larger than a predefined critical number of participating (or bounded) vehicles. In this way the speed drop mentioned above is translated into an overshot of the threshold given by the critical cluster size.

Language

  • English

Media Info

  • Media Type: CD-ROM
  • Features: Figures; References;
  • Pagination: 13p
  • Monograph Title: Symposium on the Fundamental Diagram: 75 Years (Greenshields 75 Symposium), July 8-10, 2008, Woods Hole, MA. Preprints

Subject/Index Terms

Filing Info

  • Accession Number: 01109361
  • Record Type: Publication
  • Files: TRIS, TRB
  • Created Date: Aug 25 2008 8:11AM