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.
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Authors:
- Mahnke, Reinhard
- Liebe, Christof
- Kuhne, Reinhart D
- Wang, Haizhong
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Conference:
- Symposium on the Fundamental Diagram: 75 Years (Greenshields 75 Symposium)
- Location: Woods Hole Massachusetts, United States
- Date: 2008-7-8 to 2008-7-10
- Publication Date: 2008
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
- TRT Terms: Flow speed relationships; Macroscopic traffic flow; Mesoscopic traffic flow; Traffic congestion; Traffic flow theory; Traffic models
- Uncontrolled Terms: Fundamental diagram; Traffic flow breakdown
- Subject Areas: Highways; Operations and Traffic Management; I71: Traffic Theory;
Filing Info
- Accession Number: 01109361
- Record Type: Publication
- Files: TRIS, TRB
- Created Date: Aug 25 2008 8:11AM