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DOWNSTREAM QUEUES ON UPSTREAM CAPACITY EXPANSION AT URBAN SIGNALIZED INTERSECTIONS
Xin (Alyx) Yu, E.I.T.
University of Hawaii at Manoa
Presented at the ITE Western District Annual Meeting
June 25, 2012
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Outlines
Problem Solution Application Conclusion
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PROBLEM
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Downstream Spillback
Restricted upstream capacity
Deteriorating downstream traffic conditions
CTH = 1,600 Veh/h
CTH = 1,200 Veh/h
2,000 Veh/h
Q=400 Veh/h Q=400 Veh/h
A BBefore Capacity Expansion
1,600 Veh/h
CTH = 2,000 Veh/h
CTH = 1,200 Veh/h
2,000 Veh/h
Q=0 Veh/h Q=800 Veh/h
A B
2,000 Veh/h
CTH = 1,800 Veh/h
CTH = 1,200 Veh/h
2,000 Veh/h
Q=200 Veh/h Q=600 Veh/h
A B
1,800 Veh/h
N
1,200 Veh/h
1,200 Veh/h
1,200 Veh/h
After Capacity Expansion(Theoretical Condition)
After Capacity Expansion(Practical Condition)
CTH: Capacity of Eastbound Through Movement; Q: Queue Size
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Existing Approaches
Traffic simulation/modeling Simtraffic VISSIM TransCAD EMME/2
Complex Algorithm Genetic algorithm (GA)-based Macroscopic hypothetical model
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Weaknesses of Existing Methods Data-intensive or compute-intensive Expensive to gather the data Impractical for a project in the early stage of
alternative screenings Impractical for a minor/temporary project
with a limited budget
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So we need……
A quick process to analyze downstream queuing effects
Using the basic and typically available data
Must be reliable and easy to use
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SOLUTION
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We have HCM……
Investigate capacity constraint of downstream queues by reversing and integrating the HCM procedures of intersection capacity and queue length estimation
HCM 2010: f (X,Y) = Z
f(Arrival Rate (X) , Signal Timing (Y)) = Vehicle Queue Length (Z)
Our method: f (Z,Y) = Y
f(Max Allowable Queue Storage Length , Downstream Intersection Signal Timing) = Max Downstream Allowable Arrival Rate
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Example: Is there queue spillback at EB downstream?Existing EB Downstream Entry Volume V.S. Max Downstream Allowable Arrival Rate.√ If less, no queue spillback and upstream capacity expansion is possible√ If greater or equal to, queue spillback will occur or is about to occur
Subject Intersection
Downstream Intersection
-Entry Movements
-Downstream Segment
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Spreadsheet Tools Developed using
Microsoft Excel 2007
A one page worksheet containing three sections: Inputs, Summary and Output.
Downstream Intersection
Analyzed by: Project:
Date and Time: Agency or Organization:
InputsA. Downstream Intersection Condition UnitsPosted Speed Limit mi/hr 25Distance to Upstream Int (D) ft 900Estimated Cycle Length (C) sec 120 0.7
B. Lane configuration and Signal TimingSelect Lane Group (LG) - NA TH RT NANo. of Lanes - 1 1Saturation flow veh/s/ln 0.48 0.45% LG Vol in Total Approaching Vol (Pi) - 0.80 0.20Effective Green (g) sec 84 84Arrival Type - 3 3
SummaryAvg. Approach Speed (Sa) mi/hr 34Acc/Dec Delay (da) sec 10Veh Spacing in Queue (Lv) ft 25Max Back-of-Queue Size (Q ) veh 37
Lane Group (LG) - NA TH RT NA% Veh Arriving on Green (P) - 0.7000 0.70Cyclic or Sustained Spillback - Sustained SustainedMax. Arrival Rate to LG (qi) veh/s/ln 0.35 0.33
0.44 1.66
Order of Spillback Occurrence - 1 2 Determinant Lane Group - YES NO
Output
veh/h
Location:
Downstream Arrival Capacity(Rounded to the nearest 5) 1585
Downstream Capacity Constraint Calculation Worksheet
Test Example Test Example
Xin Yu Test Example
23-Jul-11 University of Hawaii
Download available at my personal website: http://www2.hawaii.edu/~xinyu (model tab)
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APPLICATION
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Vineyard Blvd. and Punchbowl St.
Two capacity expansion options on the WB:
1. Underpass lane 2. At-grade lane
S. Vineyard Blvd
Pu
nch
bo
wl S
t
Queen Emma St
H-1 F
reeway
N
Subject IntersectionSubject Intersection
WB Downstream Intersection
WB Downstream Intersection
EB Freeway On-rampEB Freeway On-ramp
WB Downstream Approach
WB Downstream Approach
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Analysis and EvaluationInputsA. Downstream Intersection Condition UnitsPosted Speed Limit mi/hr 30Distance to Upstream Int (D) ft 635Estimated Cycle Length (C) sec 160
B. Lane configuration and Signal TimingSelect Lane Group (LG) - TH+RT TH LT NANo. of Lanes - 1 2 1Saturation flow veh/s/ln 0.45 0.45 0.45% LG Vol in Total Approaching Vol (Pi) - 0.22 0.60 0.18Effective Green (g) sec 80 80 22Arrival Type - 4 4 4
SummaryAvg. Approach Speed (Sa) mi/hr 36Acc/Dec Delay (da) sec 10Veh Spacing in Queue (Lv) ft 25Max Back-of-Queue Size (Q ) veh 26.4
Lane Group (LG) - TH+RT TH LT NA% Veh Arriving on Green (P) - 0.67 0.6667 0.18Cyclic or Sustained Spillback - Cyclic Cyclic SustainedMax. Arrival Rate to LG (qi) veh/s/ln 0.22 0.22 0.09
1.02 0.75 0.51
Order of Spillback Occurrence - 3 2 1 Determinant Lane Group - NO NO YES
Output
veh/hDownstream Arrival Capacity
(Rounded to the nearest 5) 1830
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Analysis and Evaluation
Movements of Downstream Approach
Determinant of Arrival Capacity
Downstream Arrival
Capacity (veh/hr)
Existing Arrival Volume (veh/hr)
Queue Spillback
Occurred?
Left Turn YES 1830 1200 NO
Through/Right Turn NO
Upstream Treatments Downstream Arrival Capacity (veh/hr)
Design Capacity (veh/hr)
Maximum Additional Upstream
Arrival
Spillback Occurred?
and Capacity Loss (veh/hr)
Underpass Lane 1830
1620 630 Yes, 990At-grade Lane 600 630 No, 0
Existing
With Project
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CONCLUSION
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Conclusion
This process can answer:
1. Spillback occurrence (when and where)
2. The feasibility of intersection treatments (considering intersection interactions)
This process can be used in:
1. Project screening and planning level assessment
2. Developing a prioritized list of potential capacity expansion in urban corridor.
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Questions and Comments
Xin (Alyx) Yu, E.I.T.
University of Hawaii at Manoa
Email: [email protected]
Personal Website: www2.hawaii.edu/~xinyu