1 Evaluation of Adaptive Cruise Control in Mixed Traffic Session

2 David Levinson and Xi Zou Dept. of Civil Engineering University of Minnesota

3 Outline 1.Background 2.Evaluation of Adaptive Cruise Control 3.Microscopic Traffic Simulation 4.Simulation Results 5.Conclusion & Remarks

4 What’s ACC? Features:  Forward-looking Radar  Brake-Throttle Control  Preset Speed and Inter-vehicle Headway

5 Motivations of Research To evaluate the impacts of ACC policies on traffic flow  To develop a framework to evaluate quality of traffic flow  To develop microscopic traffic simulation tools  To compare the new ACC algorithm with the existing ACC algorithms

6 Evaluation of Adaptive Cruise Control Safety –Average Headway –Headway Deviation Capacity –Minimizing Headway Traffic Flow Stability –Reducing Speed Variations

7 Simulation Scenarios Road –One-lane Pipeline –No Lane-changing

8 System Configuration Manually driven traffic: –Gipps’ Car-following Model Mixed traffic: –ACC cars mixed with Gipps’ cars Pure ACC traffic: (semi-automated) –I ndividually assigned headway/ desired speed –Constant Time Headway vs. Variable Time Headway

9 Traffic Simulation  Vehicle Dynamics (ACC vehicles)  Car-following Model  Gipps’ model

10 Adaptive Cruise Control Policies Constant Time Headway Variable Time Headway (Rajamani and Wang)

11 Inter-vehicle Spacings of ACC Policies Constant Time Headway Variable Time Headway (Rajamani and Wang)

12 Flowchart of Simulation Program

13 System Configuration Road length3212 meters Maximum size of vehicles5 meters Initial speed of vehicles17.79 m/s Maximum Speed28.9 m/s Parameters of operation Sample time (calculation cycle)0.1 second Normal simulation time duration600~900 seconds Parameters of Simulation

14 Parameters of ACC Policies Parameters of Gipps’ Model Constant Time HeadwayDesired Speed28.9 m/s Time Headway 1.0~1.2 sec Max. Acceleration 1.7 m/s 2 Variable Time Headway Max. Deceleration -3.4 m/s 2 Free Flow Speed m/s Time Headway2 seconds Parameters of Simulation

15 Traffic Demand

16 Response to Demand Pulse(CTH & Gipps) I Constant Time Headway: 0.9 Veh/sec Pulse Demand 1 sec Preset Headway CTH ACC increases traffic speed under below capacity demand

17 Response to Demand Pulse (CTH & Gipps) II Constant Time Headway:1 sec Preset Headway 1.2 Veh/sec Pulse Demand ╳ CTH ACC increases speed drop under above capacity demand

18 Headway Effects (CTH) Constant Time Headway 0.9 Veh/sec Pulse Demand 2 sec Preset Headway ╳ High preset headway reduces traffic capacity

19 Response to Demand Pulse (CTH Random Effects) Constant Time Headway: 1.2 Veh/sec Pulse Demand Preset Headway ~ max(N(1, 0.5), 0.8) ╳ The headway deviation of CTH will adversely affect traffic capacity.

20 Response to Demand Pulse (VTH & Gipps) Variable Time Headway: 1.2 Veh/sec Pulse Demand No Preset Headway VTH ACC always performs well under high demand.

21 Density-Flow Rate Relation (100% ACC)

22 Speeds with Different ACC Penetrations under Constant Demand 0.8 veh/s

23 Speed Variances with Different ACC Penetrations under Constant Demand

24 Conclusion The presence of ACC vehicles helps to increase the traffic speed under some conditions. CTH vehicles may lead to a speed drop in the case of high demand above capacity. The headway deviation of CTH ACC will adversely affect traffic capacity. VTH mixed traffic always performs well under high traffic demand. VTH is a promising alternative of CTH as it’s not detrimental to traffic flow when high demand is present.

25 Contact David M. Levinson Phone: ; Xi Zou Phone: ; Department of Civil Engineering University of Minnesota 500 Pillsbury Dr. SE, Minneapolis, MN 55455