Transcript Simulation and Analysis of Mixed Adaptive Cruise Control

Evaluation of
Adaptive Cruise
Control
in Mixed Traffic
Session 514
03-2152
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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
Control
3.Microscopic Traffic Simulation
4.Simulation Results
5.Conclusion & Remarks
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What’s ACC?
Features:
Forward-looking Radar
Brake-Throttle Control
Preset 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 Simulation
Vehicle Dynamics (ACC vehicles)
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xi  ( xides  xi )

Car-following Model
Gipps’ model


x(n, t  T )  min x a (n, t  T ), x b (n, t  T )





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Adaptive Cruise Control Policies
Constant Time Headway
1
 

 x ides   h   i   i 



 i  xi  xi 1  L  h x i
Variable Time Headway (Rajamani and Wang)




 x ides     v  x i 1  x i
m
f


 v f



1

 b i
 i   i  


x

i
1  

m


v

f



 
   b    
i
i
 i


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Inter-vehicle Spacings of ACC Policies
Constant Time Headway
Variable Time Headway (Rajamani and Wang)
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Flowchart of Simulation Program
Flowchart of Simulation: Pipeline with ACC
Program
Initialization
Platoon
Initialization
Vehicle Entry
Procedure
Initialization
Main Loop: Calculation
Main Loop: Storage
Vehicle Exit
Procedure
CarDynamics
CarFollowing
Vehicle States
Calculation
RungeKutta
CarCalculation
Veh ID
Vehicle States
Storage
time
Veh Position
Veh Speed
Road States
Calculation
Density
Road States
Storage
Space Mean Speed
Inflow
Outflow
Update time &
counter
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Parameters of Simulation
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
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Parameters of Simulation
Parameters of ACC
Policies
Parameters of Gipps’ Model
Constant Time Headway
Desired Speed
28.9 m/s
Time
Headway
Max. Acceleration
1.7 m/s2
Max.
Deceleration
-3.4 m/s2
Time Headway
2 seconds
1.0~1.2 sec
Variable Time Headway
Free Flow
Speed
31.78 m/s
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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 Demand
1 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 Headway
1.2 Veh/sec Pulse Demand
╳ CTH ACC increases speed drop under above
capacity demand
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Headway Effects (CTH)
Constant Time Headway
0.9 Veh/sec Pulse Demand
2 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 Demand
Preset 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 Demand
No Preset Headway
 VTH ACC always performs well under high demand.
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Flow Rate veh/s
Density-Flow Rate Relation (100% ACC)
2.0
1.9
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Density vs. Flow Rate:
Response to Over-Capacity Triangle Demand
VTH Veh
CTH Veh
10
20
30
40
50
60
Density veh/km
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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: [email protected]
Xi Zou
Phone: 612-626-0024; Email: [email protected]
Department of Civil Engineering
University of Minnesota
500 Pillsbury Dr. SE, Minneapolis, MN 55455
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