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Lec 11, Ch6, pp173-187: Principles of traffic flow (objectives)

Lec 11, Ch6, pp173-187: Principles of traffic flow (objectives). Know the primary elements of traffic flow Know the difference between TMS and SMS Know the general equation relating flow, density, and space mean speed Be able to draw the fundamental diagram of traffic flow

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Lec 11, Ch6, pp173-187: Principles of traffic flow (objectives)

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  1. Lec 11, Ch6, pp173-187: Principles of traffic flow (objectives) • Know the primary elements of traffic flow • Know the difference between TMS and SMS • Know the general equation relating flow, density, and space mean speed • Be able to draw the fundamental diagram of traffic flow • Know thoroughly the characteristics of two most popular macroscopic traffic flow models

  2. What we cover in class today… • Time-space diagram • Primary elements of traffic flow • How to compute TMS and SMS • Flow-density relationship • Fundamental diagram of traffic flow • Macroscopic traffic flow models: Greenshields model and Greenburg model

  3. Time-space diagram (A microscopic way of looking at traffic flow 1 Time headway 2 3 4 5 Distance 6 Space headway Time

  4. Time mean speed vs. space mean speed Time mean speed (TMS): Space mean speed (SMS): (Review Example 6-1)

  5. Flow-density relationships Flow = (density) x (Space mean speed) Space mean speed = (flow) x (Average space headway) where Average space headway = SMS/(Average time headway) where

  6. Fundamental diagram of traffic flow (flow vs. density) Optimal flow or capacity,qmax Mean free flow speed, uf Optimal speed, uo Flow (q) Speed is the slope. u = q/k Uncongested flow Congested flow Jam density, kj Optimal density, ko Density (k)

  7. Fundamental diagram of traffic flow (SMS vs. density & SMS vs. flow) uf uf Uncongested flow SMS SMS Congested flow 0 0 kj qmax Density Flow SMS vs. density SMS vs. flow

  8. Greenshields model Nice characteristics of the Greenshields model: This model works for all k = 0 to k = kj

  9. Greenburg model Characteristics of the Greenburg model: or or This model does not work near k = 0. Do you know why?

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