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Truck Impact in the Performance of Roundabout:
A Dedicated Truck Slip Lane
NCAMPO 2013 Conference Winston-Salem, NC May 15 - 17, 2013
Majed Al-Ghandour, Ph.D., PE, CPM Program Development Branch
NCDOT
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Outline
• Introduction • Objectives • Experiment Approach & Methodology • Analysis • Results and Discussion of Truck Traffic Simulation • Conclusions & Recommendations • Future Research
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Challenges
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Challenges
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Challenges
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Challenges
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Challenges
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“Electric generator 1.98 million pounds The trailer, as rigged, is 300 ft There are 36 rows of axles, each with 8 tires. (288 total) Add in 5 each 10 wheel heavy duty road tractors (2 pulling and 3 pushing) Tire count, for the moment, is 338”
338 Wheeler
Source: [email protected]
Challenges
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Challenges Reactor Transport In Canada
Source: Phil Weber, M.Eng., P.Eng. Service Group Manager, Roundabouts
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Slip Lane
• A slip lane, sometimes incorporated with a roundabout, is a separate (exclusive) right-turn lane that lies adjacent to a roundabout.
• A slip lane:
• Facilitates right-turn traffic flow.
• Reduces approach delay by allowing right-turning movements to bypass the roundabout.
• Reduces vehicle conflicts.
NCHP Report 572 (2007): Roundabouts in the United States. National Research Council, Transportation Research Board, Washington, D.C.
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Slip Lane Used in NC
Slip Lane
Styers Ferry Road and Utility Road: Roundabout with Two Slip Lanes
Clemmons, NC
NC 801 and I-40 (Exit 180) Advance, NC
Source: Al-Ghandour, et. al. 2011
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Roundabout Operational Performance
Three capacity methods: • Gap acceptance • Empirical regression • Hybrid (Gap and Empirical)
[FHWA 2000]; [NCHRP Report 572 2007] ;[NCHRP Report 672 2010]:
cvcrit ec 0010.01130 −=
Where, c crit = capacity of the critical lane on the approach (vehicles per hour) vc = conflicting flow (vehicles per hour).
(Equation 4-3)
Introduction
vc
va
Appr
oach
Flo
w
[NCHRP Report 672 2010]:
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[NCHRP Report 672 2010]
pceexvpcebypass ec ,0010.0
, 1130 −=Where, c bypass, pce = capacity of the bypass lane opposed by one existing lane, adjusted for heavy vehicles, pc/h vex,pce = conflicting exiting flow, pc/h.
• The capacity of a yielding slip lane opposed by one exiting lane approach or by two exiting lanes can be approximately
Introduction
(Equation 4-7)
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Experiments Objectives
• To assess proposed truck dedicated slip lane impact on roundabout operational performance(delay and traffic volumes ).
• To evaluate operational performance—vehicle
delays—of single-lane roundabouts with a slip lane, under various exit control treatments (yield, free-flow, and no slip lane) and under different right-turning truck traffic, using simulation.
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Approach
Methodology
Development of Experimental Scenarios
Analytical
Framework (Flow charts)
Literature Review Inputs
Process
Output
VISSIM
Conflicting Flow Analysis
Dedicated Truck Slip Lane Operational Performance
Sensitivity
Part is from Source: Al-Ghandour, et. al. 2011
Variable Symbols Variable Description Level of Description
SLT Slip lane type configurations at
exits
Yield and Free-Flow.
Vsl Slip lane volume as dominant turn
50,100, 150, 200, 250, 300, 350, 400, 450, and 500 vehicles per hour.
Vapproach Approach entry volume
Approach entry is calculated based on dominant right-turn volume and scenario.
S1= No Slip Lane S2= Yied Slip Lane S3= Free-Flow Slip
Lane
Traffic percentage distribution flow
matrices
Balanced scenarios: Balanced flow with 33 percent flow for all turns.
Trucks Trucks traffic percentages
Truck0: 0% - no trucks. Truck5: 5% - low trucks. Truck45: 45% - moderate trucks. Truck80: 80% - high trucks - Dedicated trucks lane.
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Scenarios Methodology Experimental Scenarios Scenario Experiment Design
Sample of Traffic Percentage Distribution Flow Pattern for Scenario S1 (No Slip Lane)
Methodology
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Basic Concept of Conflicting Flow Analysis Approach volumes (Va) Exit volumes (Vexit) Conflicting volumes (Vc) Circulating volumes (Vcirc) Conflicting off slip lane approach volume (Vm) Slip lane volumes (Vsl)
S133%
0.33
0.
34 0
.33
0.33 0.34 0.33
0.33 0.34 0.33
EBW
WBE
NBS
SB
Vc
0.33 0.34 0.33
Va
Vexit
Vcirc
9 8 7
12
11
10
1 2 3
4
5
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NB: Northbound Approach
Sample of Traffic Percentage Distribution Flow Pattern for Scenario S2 (Yield Slip Lane)
Methodology
Example: Va= volumes at (7) + volumes at (8) + volumes at (9) =0.33+ 0.34+0.33= 1.0 Vexit= 1.0 Vc= volumes at (3) + volumes at (11) + volumes at (12) = 0.33+0.34+0.33=1.0 Vcirc=volumes at Vc + volumes at Va = 1.0 + 1.0 = 2.0 Vm= 0
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N
S233%
0.33
0.
34 0
.33
0.33 0.34 0.33
0.33 0.34 0.33
EBW
NBS
SB
Vsl
0.33 0.34 0.33
Vsl
1 2 3
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5
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9 8 7
12
11
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NB: Northbound Approach
Yield
SL: Slip Lane
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N
S333%
0.33
0.
34 0
.33
0.33 0.34 0.33
0.33 0.34 0.33EB
WWB
NB
S
SB
Vsl
0.33 0.34 0.33
Vsl
NB: Northbound Approach
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5
6
1 2 3
12
11
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9 8 7
Free-Flow
Slip Lane:
No merging at the
downstream of the
free-flow lane
Sample of Traffic Percentage Distribution Flow Pattern for Scenario S3 (Free-Flow Slip Lane)
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VISSIM Simulation Assumptions
• A single-lane roundabout with one slip lane. • Traffic percentage distribution flow matrices were
developed.
• A slip lane was assumed to be placed at the northbound (NB) entry to the roundabout.
• All right turning traffic we have assumed will be entered the slip lane rather than the roundabout.
Methodology
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VISSIM Simulation Assumptions.. Continued
• Several defaults values kept for driver behaviors. • For each simulation scenario, 20 VISSIM runs were
executed using different random number seeds. • A truck dedicated slip lane designation means only for
truck - no vehicles allowed.
Methodology
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Performance Analysis: Sample of Microsimulation VISSIM
VISSIM 5.10
Methodology Layout of a Single-Lane Roundabout in VISSIM
VISSIM MOE: Average vehicle delay in seconds
a) No Slip Lane
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Performance Analysis: Sample of Microsimulation VISSIM
VISSIM 5.10
Methodology Layout of a Single-Lane Roundabout in VISSIM
VISSIM MOE: Average vehicle delay in seconds
b) Yield Slip Lane
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Performance Analysis: Sample of Microsimulation VISSIM
VISSIM 5.10
Methodology Layout of a Single-Lane Roundabout in VISSIM
VISSIM MOE: Average vehicle delay in seconds
c) Free-Flow Slip Lane
Scenario
Vsl: Slip Lane Volume,
Right-Turn Volume
(vehicle/hour)
(33%)
SL NB RBT
S3 Free-Flow
50 (Low) 0.2 0.7 0.9 250 (Moderate) 8.9 12.1 34.5 500 (High) 25.5 28.8 43.7
S2 Yield
50 (Low) 0.4 0.7 0.9 250 (Moderate) 10.9 13.2 34.8 500 (High) 27.4 29.6 44.0
S1 No Slip
50 (Low) 0.9 1.0 1.0 250 (Moderate) 40.9 41.2 41.0 500 (High) 44.0 43.5 46.3
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Sample - Summary of VISSIM Average Delays – Base Case: No Trucks (Truck0)
Analysis
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Summary of VISSIM Average Delays—Trucks
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Sample of Outputs from VISSIM: Roundabout Average Delay per Slip Lane Exit Types for Scenario S1 (33%)
Analysis No Trucks
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5% Trucks
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45% Trucks
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Sample of Outputs from VISSIM: Roundabout Average Delay per Slip Lane Exit Types for Scenario S1 (33%)
Analysis 80%Trucks
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36 No Slip Lane Yield Slip Lane Exit Type Free-Flow Slip Lane Exit Type
Results: Performance Analysis Summary of Results for Trucks: VISSIM Percentage Change in Average Delays:
Balanced Scenarios (S2 and S3): Compared to Scenario S1 (No Slip Lane)
Scenario Slip Lane Exit Type
Vsl: Slip Lane Volume, Right-Turn Volume (vehicles per hour) at NB Approach
Percent of Reduction of Average Delay (sec/vehicle) Truck Traffic Percentages
Statistical Results
Truck0 (0%)
No truck
Truck5 (5%) truck
Truck45 (45%) truck
Truck80 (80%) truck
RBT RBT RBT RBT
S3 Free-Flow
50 (Low) Average -10% -30% -15% -15% 250 (Med) Average* -16% -6% -1% -3% 500 (High) Average* -6% -4% -3% -4%
S2 Yield
50 (Low) Average -10% -30% -15% -15% 250 (Med) Average* -15% -6% -1% -2% 500 (High) Average* -5% -4% -3% -3%
All Averages S3 Free-Flow Average all
Reductions
-9.0% -9% -9% -10% -9%
S2 Yield -8.0% -8% -9% -10% -8%
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Modern Roundabout Design Features
38 Source: NCDOT- B-2965 Roundabout Details- Roadway Design Unit US 64-NC 33 BRIDGE 24, OVER TAR RIVER, Edgecombe County
39 Source: NCDOT- B-3637 Roundabout Details- Roadway Design Unit BRIDGE 37 OVER I-40 ON NC 801- DAVIE County, NC
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Conclusions & Recommendations (1 of 2)
Trucks are most challenging element for Roundabout Design. Design a via large truck aprons and outer overrun areas, if
possible. VISSIM Simulation results confirm that average delay and
circulating conflict volumes in a roundabout with a slip with truck traffic lane are related exponentially to slip lane volumes up to a saturation point.
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For example, results showed the overall roundabout delay was reduced by 9% with the use of a dedicated truck free-flow slip lane; and 8% with use of a yield slip lane.
A truck managed “dedicated” slip lane with free- flow and yield exit types has shown advantages over no slip lane in reducing overall roundabout average delay.
Add slip lanes for each approach if possible.
Conclusions & Recommendations (2 of 2)
Disclaimer: These are the author recommendations and does not present the NCDOT guidelines or policies.
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Future Research
• A study is to evaluate the impact of trucks at roundabouts when returning left-turn trips on roundabout circulating lane. • Further analysis address other truck managed slip lane exit types such as those using a ramp metering signal, and also assess the impact of mix of buses and trucks traffic using a dedicated slip lane.
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Curious
In Alberta, Canada
Source: Phil Weber, M.Eng., P.Eng. Service Group Manager, Roundabouts
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More Curious
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Shanghai, China Interesting
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Contact Information & Questions Majed N. Al-Ghandour, Ph.D., P.E., CPM, M.ASCE Assistant Branch Manager, Engineering Manager Program Development Branch - NCDOT 1534 Mail Service Center Raleigh, NC 27699-1534 Tel.: 919-707-4621 Fax: 919-733-3585 Email: [email protected]
THANK YOU
