Car-following Models for Motorway Traffic Jiao Wang Research Student Institute for Transport Studies University of Leeds, UK

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

3 Introduction Car-following models 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

4 - Closing following (high flow, high speed) Flow-Occupancy Diagram near Toronto (Hall et al. 1986)

5 The Development of the Model Combination of safety-distance model and close- following model with different reaction times applied for different traffic states: 1. 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)

6 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

7 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)

8 Alert and non-alert states Alert and non-alert states

9 Close-following state Close-following state

10 Transitions between different driving states Transitions between different driving states

11 Test Design of Models Simulation 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)

12 Simulation tests and results analysis The effects of the reaction times The effects of the reaction times The bigger the difference between the reaction times for different states, the clearer the hysteresis loop

13 Simulated close-following spiral Individual vehicles DV-DX diagram Close-following

14 Simulated speed-time diagram

15 A simulated flow-occupancy diagram

16 Backward propagated shockwaves Plots of individual vehicle trajectories simulated by the new model

17 The speeds of the backward The speeds of the backward propagated shockwave

18 The simulated and observed gap distributions

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

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