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Topic 5 Platoon and Dispersion

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Topic 5 Platoon and Dispersion. TRANSYT-7F MODEL. TRANSYT is a computer traffic flow and signal timing model, originally developed in UK. TRANSYT-7F is a U.S. version of the TRANSYT model, developed at U of Florida (Ken Courage)

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slide1
Topic 5

Platoon and Dispersion

slide2

TRANSYT-7F MODEL

  • TRANSYT is a computer traffic flow and signal timing model, originally developed in UK.
  • TRANSYT-7F is a U.S. version of the TRANSYT model, developed at U of Florida (Ken Courage)
  • TRANSYT-7F has an optimization component and a simulation component.
  • The simulation component is considered as a macroscopic traffic simulation, where vehicles are analyzed as groups.
  • One of the well known elements about TRANSYT-7F’s traffic flow model is the Platoon Dispersion model.
slide3

WHY MODEL PLATOON DISPERSION?

  • Platoons originated at traffic signals disperse over time and space.
  • Platoon dispersion creates non-uniform vehicle arrivals at the downstream signal.
  • Non-uniform vehicle arrivals affect the calculation of vehicle delays at signalized intersections.
  • Effectiveness of signal timing and progression diminishes when platoons are fully dispersed (e.g., due to long signal spacing).
slide4

PLATOON DISPERSION MODEL

  • For each time interval (step), t, the arrival flow at the downstream stopline (ignoring the presence of a queue) is found by solving the recursive equation
slide5

PLATOON DISPERSION

Flow rate at interval t, qt

100

% Saturation

50

0

Time, sec

Start Green

T = 0.8 * T’

Flow rate at interval t + T, Q(T+t)

100

% Saturation

50

0

Time, sec

slide6

CLOSED-FORM PLATOON DISPERSION MODEL

s

Flow rate, vph

v

0

tq

tg

Time

C

slide9

CLOSED-FORM PLATOON DISPERSION MODEL (1~tq)

For 1~tq with s flow

Maximum flow downstream occurs at T+tq with upstream s flow

slide10

BEYOND (1~tq)

From the original equation:

s no longer exists, but zero flow upstream

t = tq +1 ~ ∞

  • This is mainly to disperse the remaining flow, Qs,max. Upstream flow is zero
  • The same procedure for the non-platoon flow
  • The final will be the sum of the two
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EXAMPLE

  • Vehicles discharge from an upstream signalized intersection at the following flow profile. Predict the traffic flow profile at 880 ft downstream, assuming free-flow speed of 30 mph, α = 0.35; β = 0.8.

Use time step = 1 sec/step

3600

Flow rate, vph

1200

0

16

28

Time

C=60 sec

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