1 Optimization of ALINEA Ramp- metering Control Using Genetic Algorithm with Micro-simulation Lianyu Chu and Xu Yang California PATH ATMS Center University of California, Irvine
Dec 21, 2015
1
Optimization of ALINEA Ramp-metering Control Using Genetic Algorithm with
Micro-simulation
Lianyu Chu and Xu Yang
California PATH ATMS Center
University of California, Irvine
2
Overview
• Background: ALINEA• Genetic Algorithm• Optimization Framework• Simulation Modeling• Optimization Study• Conclusion Remarks
3
Background
• ALINEA, proposed by Papageorgiou in 1990s• A local feedback ramp-metering strategy • Remarkably simple, highly efficient and easily
implemented• Good performance
– Field tests– Simulation-based studies
• Potential applications
5
Background : ALINEA
• Parameter values in field tests:– Desired occupancy O* : 0.18 -- 0.31
– KR =70, in real-world experiments
– Downstream detector location: 40 m -- 500 m downstream
– Update cycle t: 40 seconds -- 5 minutes
6
Background: Purposes
• How to optimize ALINEA’s operational parameters in order to maximize its performance?
• Method: -> Hybrid method: simulation + GA
7
Genetic Algorithm
• Mimic the the mechanics of natural selection and evolution
• Proven to be a useful method for optimization
• Useful when there are too many parameters to be considered
8
Optimization Framework
MOE
GA
Time-dependentTravel demands
PARAMICSsimulation
ALINEAramp-metering algorithm
PerformanceMeasure
Ramp MeteringController
Loop DataAggregator
ParameterValues
9
Simulation Modeling
• Study site
Traffic direction
Irvine Central Dr
SR-133
Sand Cnyn. Jeffery Dr Culver Dr
6.21 5.74 5.55 5.01 4.03 3.86 3.31 3.04 2.35 1.93 1.57 1.11 0.93 0.6 (post-mile)
1 2 3 7 6 5 4
10
Simulation Modeling
• Model Calibration
Loop station @ postmile 3.04 (simulation)
0
20
40
60
80
100
0 20 40 60 80
Percent occupancy
30-s
ec v
olum
e
Loop station @ postmile 3.04 (real world)
0
20
40
60
80
100
0 20 40 60 80
Percent occupancy
30-s
ec v
olum
e
11
Optimization Study
• MOE: Total vehicle travel time (TVTT)Ni,j: total number of vehicles that actually traveled
between origin i and destination j
Di,j: travel demand from origin i to destination j for the whole simulation time (Di,j is not equal to Ni,j because of the randomness of the micro-simulation)
Tki,j: travel time of the kth vehicle that traveled from origin i to destination j
)/( ,, 1
,,
,
jiji
N
k
kjiji NTDTVTT
ji
12
Optimization Study
• Setup the range of calibrated parameters for ALINEA
Parameter RangeRegulator KR 10 ~ 300Desired occupancy 10% ~ 40%Update cycle of metering rate 10~300 secLocation of downstream detector 0~600 m
13
Optimization Study
• The best, worst and average fitness values of each generation
1.46
1.48
1.5
1.52
1.54
1.56
1.58
1 2 3 4 5 6 7 8 9 10
Best Average Worst Fixed-time
Generation
14
Optimization Study
• The results of optimized ALINEA parameters
Parameter RangeRegulator KR 70~200Desired occupancy 19~21%
30~31%Update cycle of metering rate 30~60 secLocation of downstream detector 120~140 m
15
Findings
• When the regulator KR, used for adjusting the constant disturbances of the feedback control, is within the range from 70 to 200, the metering system is found to perform well.
• The optimal location of the downstream detector is found to be between 120~140 meters downstream of the on-ramp nose in our simulation study.
16
Findings
• The update cycle of the metering rate implementation gives the best system performance when it ranges from 30 to 60 seconds in our study.
• The desired occupancy of the downstream detector station is found to be within two ranges, either from 19% to 21% or around 30% to 31%. Finally, 19% to 21% is selected for its better network reliability performance.
18
Conclusions
• This paper presents a hybrid GA-simulation method to find the optimized parameter values for the ALINEA control. This method is effective to find the optimized parameter values.
• Practitioners can use our optimization results as a basic operational reference if they implement ALINEA control in the real world.
19
Conclusions
• This study shows that micro-simulation can be used to calibrate and optimize the operational parameters of ramp metering control. Potentially, micro-simulation may also be used to fine-tune parameters for various other ITS strategies.