Carfollowing Models for Motorway Traffic

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Car-following Models for Motorway Traffic

• Jiao Wang
• Research Student
• Institute for Transport Studies
• University of Leeds, UK
• trajwa_at_leeds.ac.uk

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Contents

• Introduction
• Development of the model
• Theoretical explanations
• Experiment design
• Simulation tests
• Conclusions

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Introduction

• Car-following models
• Psycho-physical models (e.g. GM models)
• Safety-distance models (e.g. Gipps model)
• Action-points models ( Leutzbach and Wiedemann,
  1986)
• Motorway traffic flow characteristics
• - Traffic breakdown, shockwaves
• - Traffic hysteresis

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Flow-Occupancy Diagram near Toronto (Hall et al.
1986)

• - Traffic hysteresis
• - Closing following (high flow, high speed)

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The Development of the Model
Combination of safety-distance model and
close-following model with different reaction
times applied for different traffic states1.
At low speed ALERT STATE (with short reaction
time)2. At higher speed NON-ALERT (with
longer reaction time) OR, CLOSE-FOLLOWING
(with short reaction time)
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Car-following at alert and non-alert states
-Two Constraints on the Speed
Based on the Gipps safety-distance
model 1.Vehicle can accelerate freely to its
desired speed
2. Safe stop Ensure vehicle can bring his
vehicle to a safe stop should the vehicle ahead
came to a sudden stop
NO!
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• The Car-following model during close-followings
  state
• Based on the close-following spiral in a plane of
  relative speed and space gap (Brackstone et al.
  2002)

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• Alert and non-alert states

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• Close-following state

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• Transitions between different driving states

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Test Design of Models Simulation

• Single Lane, 1080m

• No Overtaking

• No Considering of Curvature

• 85 vehicle gradually Enter/ Exit every 20 s

• Detectors at 270m, 540m, 810m

• Increased demand stage (1700s)

• Constant demand stage (200s)

• Decreased demand stage (1700s)

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Simulation tests and results analysis

• The effects of the reaction times

The bigger the difference between the reaction
times for different states, the clearer the
hysteresis loop
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Simulated close-following spiral

• Individual vehicles DV-DX diagram

Close-following
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Simulated speed-time diagram
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A simulated flow-occupancy diagram
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Backward propagated shockwaves

• Plots of individual vehicle trajectories
  simulated by the new model

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• The speeds of the backward
• propagated shockwave

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The simulated and observed gap distributions
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Conclusions

• The new model is able to represent
• Traffic hysteresis
• - responds well to the alert reaction time and
  non-alert reaction time
• Speed drop
• Shockwave propagation
• Close-following behaviour

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Thanks!