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Traffic Flow Analysis II Lecture 13 CE 2710 Norman Garrick

Traffic Flow Analysis II Lecture 13 CE 2710 Norman Garrick. Representing Traffic Flow. The fundamental equation of traffic stream flow is q = uk

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Traffic Flow Analysis II Lecture 13 CE 2710 Norman Garrick

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  1. Traffic Flow Analysis II Lecture 13 CE 2710 Norman Garrick Norman W. Garrick

  2. Representing Traffic Flow The fundamental equation of traffic stream flow is q = uk This equation is used in conjunction with the Traffic Flow Curves (next slide) in an attempt to characterize traffic flow on a macroscopic level. However, it should be understood that these analytical representation of traffic flow does fully depicting real life traffic which is a complex and non-linear phenomena. The complexity derive from the fact that we have a large number of vehicles interacting in a way that does not follow the laws of mechanics due to the reaction of the HUMAN driver Norman W. Garrick

  3. Traffic Flow Curves u k Norman W. Garrick

  4. Traffic Flow Curves u k Norman W. Garrick

  5. Traffic Flow Curves u u ? k q Norman W. Garrick

  6. Traffic Flow Curves u u k q Norman W. Garrick

  7. Traffic Flow Curves u u k q Norman W. Garrick

  8. Traffic Flow Curves u u k q One important point to note, FLOW increase with SPEED but only up to a point In other words, higher SPEED does not necessarily mean high FLOW Why? What is the physical phenomenon that cause this? Norman W. Garrick

  9. Traffic Flow Curves u u k q q ? k Norman W. Garrick

  10. Traffic Flow Curves u u k q q k Maximum FLOW occurs at medium CONCENTRATION Norman W. Garrick

  11. What is the Maximum Theoretical Flow on a Highway? If we haveCONCENTRATION and SPEED under different conditions we could estimate MAXIMUM FLOW But the relationship between SPACE (or concentration) and SPEED depends on how the average person drive. This characterization of how people drive is some times refer to as the ‘safety regime’. And as we have discussed before, this safety regime is hard to characterize and depends on factors such as weather, age of drivers and other cultural factors The figure in the next slide is considered to give a SPACE/SPEED relationship that comes close to reality for American driving conditions Norman W. Garrick

  12. Calculating Maximum FlowSpacing versus Speed Spacing, ft Norman W. Garrick

  13. Calculating Maximum FlowSpeed versus Concentration (u-k) u k = 1 / s(ave) k Norman W. Garrick

  14. Calculating Maximum FlowFlow versus Speed (u-q) u q In theory qmax occurs at speed of about 35 mph Norman W. Garrick

  15. Calculating Maximum FlowFlow versus Concentration (q-k) qmax = 2000 veh/hr q = uk q k Norman W. Garrick

  16. Traffic Flow CurvesMaximum Flow, Jam Concentration, Freeflow Speed u u uf qmax kj k q q qmax qmax - maximum flow kj - jam concentration u = 0, k = kj k uf - free flow speed k = 0, u = uf Norman W. Garrick Norman W. Garrick

  17. What is the Jam Concentration? u k Norman W. Garrick

  18. What is the Freeflow Speed? u k Norman W. Garrick

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