majed al -ghandour, ph.d., pe, cpm program development ...€¦ · 16/05/2013 · 1.98 million...

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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

5

Challenges

6

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

6

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

4

5

6

9 8 7

12

11

10


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


4

5

6

1 2 3

12

11

10

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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VISSIM 5.10



b) Yield Slip Lane

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VISSIM 5.10



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


S1 No Slip


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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

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

mailto:[email protected]

majed al -ghandour, ph.d., pe, cpm program development ...€¦ · 16/05/2013 · 1.98 million...

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