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Evaluation of Adaptive Cruise

Control in Mixed Traffic  

Session 51403-2152

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David Levinson and Xi Zou

Dept. of Civil Engineering University of Minnesota

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Outline  

1.Background 2.Evaluation of Adaptive Cruise

Control3.Microscopic Traffic Simulation4.Simulation Results 5.Conclusion & Remarks

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What’s ACC?

Features:Forward-looking RadarBrake-Throttle ControlPreset Speed and Inter-vehicle Headway

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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

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Evaluation of Adaptive Cruise Control

• Safety– Average Headway – Headway Deviation

• Capacity– Minimizing Headway

• Traffic Flow Stability– Reducing Speed Variations

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Simulation Scenarios

• Road– One-lane Pipeline– No Lane-changing

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System Configuration

• Manually driven traffic:– Gipps’ Car-following Model

• Mixed traffic:– ACC cars mixed with Gipps’ cars

• Pure ACC traffic: (semi-automated)– Individually assigned headway/ desired speed– Constant Time Headway vs. Variable Time

Headway

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Traffic SimulationVehicle Dynamics (ACC vehicles)

Car-following ModelGipps’ model

1( )i ides ix x x

),(),,(min),( TtnxTtnxTtnx ba

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Adaptive Cruise Control PoliciesConstant Time Headway

Variable Time Headway (Rajamani and Wang)

iiii

iiides

xhLxx

hx

1

1

i

f

i

m

ii

iii

f

iifmides

b

v

x

bv

xxvx

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Inter-vehicle Spacings of ACC PoliciesConstant Time Headway

Variable Time Headway (Rajamani and Wang)

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Flowchart of Simulation Program

P rogramInitialization

P latoonInitialization

Road S tatesCalc ulation

Vehic le EntryP roc edure

Vehic le ExitP roc edure

Vehic le S tatesS torage

Vehic le S tatesCalc ulation

Veh ID

tim e

Veh S peed

Veh P os ition

Road S tatesS torage

M ain Loop: Calc ulation

M ain Loop: S torage

D ens ity

S pac e M ean S peed

O utf low

Inflow

Update tim e &c ounter

In itialization

F lo w c ha rt o f S im u la tio n: P ip e line w ith A C C

CarF ollow ing

RungeKutta

C a rD y n a m ic s

CarCalc ulation

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System Configuration

Road length 3212 meters

Maximum size of vehicles 5 meters

Initial speed of vehicles 17.79 m/s

Maximum Speed 28.9 m/s

Parameters of operation

Sample time (calculation cycle) 0.1 second

Normal simulation time duration 600~900 seconds

Parameters of Simulation

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Parameters of ACC Policies

Parameters of Gipps’ Model

Constant Time Headway

Desired Speed 28.9 m/s

Time Headway

1.0~1.2 sec

Max. Acceleration 1.7 m/s2

Variable Time Headway Max. Deceleration

-3.4 m/s2

Free Flow Speed 31.78 m/s

Time Headway2

seconds

Parameters of Simulation

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Traffic Demand

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Response to Demand Pulse(CTH & Gipps) I

Constant Time Headway: 0.9 Veh/sec Pulse Demand1 sec Preset Headway CTH ACC increases traffic speed under below capacity demand

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Response to Demand Pulse (CTH & Gipps) II

Constant Time Headway:1 sec Preset Headway1.2 Veh/sec Pulse Demand╳ CTH ACC increases speed drop under above capacity demand

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Headway Effects (CTH)

Constant Time Headway0.9 Veh/sec Pulse Demand2 sec Preset Headway

╳ High preset headway reduces traffic capacity

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Response to Demand Pulse (CTH Random Effects)

Constant Time Headway: 1.2 Veh/sec Pulse DemandPreset Headway ~ max(N(1, 0.5), 0.8)╳ The headway deviation of CTH will adversely affect traffic capacity.

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Response to Demand Pulse (VTH & Gipps)

Variable Time Headway: 1.2 Veh/sec Pulse DemandNo Preset Headway

VTH ACC always performs well under high demand.

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Density-Flow Rate Relation (100% ACC)

0.00.10.20.30.40.50.60.70.80.91.01.11.21.31.41.51.61.71.81.92.0

Density vs. Flow Rate: Response to Over-Capacity Triangle Demand

CTH Veh

VTH Veh

Flo

w R

ate

ve

h/s

Density veh/km

10 20 30 40 50 60

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

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Speed Variances with Different ACC Penetrations under Constant Demand

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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.

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Contact

David M. Levinson Phone: 612-625-6354; Email: levin031@tc.umn.edu

Xi Zou Phone: 612-626-0024; Email: zoux0015@tc.umn.edu

Department of Civil EngineeringUniversity of Minnesota

500 Pillsbury Dr. SE, Minneapolis, MN 55455