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Roundabout Capacity Analysis Framework
Roundabout Capacity Analysis Framework
Presented By:Dave Stanek &
Joel RabinovitzFehr & Peers
Presented By:Dave Stanek &
Joel RabinovitzFehr & Peers
Source: FHWA, Dokken Engineering
Presentation OverviewPresentation Overview
• Roundabout Analysis Framework • Roundabout Analysis Methods & Software• Case Study #1 – SR 32 in Chico, CA• Case Study #2 – Kietzke Lane in Reno, NV
• Roundabout Analysis Framework • Roundabout Analysis Methods & Software• Case Study #1 – SR 32 in Chico, CA• Case Study #2 – Kietzke Lane in Reno, NV
Analysis FrameworkAnalysis Framework
Analysis FrameworkAnalysis Framework
• FHWA Guidelines– ADT volume thresholds– Peak hour entering vs. circulatory flow
thresholds
• Analysis Software– Conduct sensitivity testing – Understand methodology used
• FHWA Guidelines– ADT volume thresholds– Peak hour entering vs. circulatory flow
thresholds
• Analysis Software– Conduct sensitivity testing – Understand methodology used
Simulation ChecklistSimulation Checklist
• When to Use– V/C ratios are > 0.85– Corridor or system– Unique geometry (5-legs, adjacent
signal, etc.)
• Review LOS results• Review queuing results• Visually inspect simulation• Conduct sensitivity testing
– NCRHP 572 gap acceptance
• When to Use– V/C ratios are > 0.85– Corridor or system– Unique geometry (5-legs, adjacent
signal, etc.)
• Review LOS results• Review queuing results• Visually inspect simulation• Conduct sensitivity testing
– NCRHP 572 gap acceptance
Analysis MethodsAnalysis Methods
• Macroscopic Models– For isolated locations– Analyze vehicle flows– HCM 2000, FHWA, NCHRP 572, RODEL,
& SIDRA
• Microscopic Models– For system analyses– Analyze individual vehicles & drivers– SimTraffic, Paramics, & VISSIM
• Macroscopic Models– For isolated locations– Analyze vehicle flows– HCM 2000, FHWA, NCHRP 572, RODEL,
& SIDRA
• Microscopic Models– For system analyses– Analyze individual vehicles & drivers– SimTraffic, Paramics, & VISSIM
HCM 2000HCM 2000
• Only one-lane roundabouts
• LOS thresholds are undefined
• Results are a range of v/c ratios
• Use Synchro or HCS+ to calculate
• Only one-lane roundabouts
• LOS thresholds are undefined
• Results are a range of v/c ratios
• Use Synchro or HCS+ to calculate
FHWAFHWA
• Roundabouts: An Informational Guide (FHWA, 2000)
• Equations for delay and queue length
• For one & two lane roundabouts with regular geometry (3 or 4 legs)
• Recommends design to V/C of 0.85
• Use Traffix or formula
• Roundabouts: An Informational Guide (FHWA, 2000)
• Equations for delay and queue length
• For one & two lane roundabouts with regular geometry (3 or 4 legs)
• Recommends design to V/C of 0.85
• Use Traffix or formula
NCHRP 572NCHRP 572
• NCHRP Report 572: Roundabouts in the United States (TRB, 2007)
• Equations for delay and queue length
• For one & two lane roundabouts with regular geometry (3 or 4 legs)
• Based on U.S. data, but a limited sample size
• NCHRP Report 572: Roundabouts in the United States (TRB, 2007)
• Equations for delay and queue length
• For one & two lane roundabouts with regular geometry (3 or 4 legs)
• Based on U.S. data, but a limited sample size
RODELRODEL
• Barry Crown, UK
• Regression equations based on observations of UK intersections
• Design elements determine approach capacity (diameter, entry width, etc.)
• Interactive design / operations analysis
• Barry Crown, UK
• Regression equations based on observations of UK intersections
• Design elements determine approach capacity (diameter, entry width, etc.)
• Interactive design / operations analysis
RODELRODEL
RODELRODEL
• Limitations– Empirical data includes experimental
observations– Uses equations calibrated to UK drivers
and UK vehicles– Capacity is reached with small
increases in volumes– Ignores circulatory or exit capacity– Ignores bypass lanes
• Limitations– Empirical data includes experimental
observations– Uses equations calibrated to UK drivers
and UK vehicles– Capacity is reached with small
increases in volumes– Ignores circulatory or exit capacity– Ignores bypass lanes
SIDRASIDRA
• Akcelik & Associates, Australia• Uses gap acceptance and lane
utilization to determine capacity• Can change headway values to
calibrate to local conditions – Environmental Factor
• Limitations– LOS results not always consistent with
predicted V/C or queues– Ignores bypass lanes
• Akcelik & Associates, Australia• Uses gap acceptance and lane
utilization to determine capacity• Can change headway values to
calibrate to local conditions – Environmental Factor
• Limitations– LOS results not always consistent with
predicted V/C or queues– Ignores bypass lanes
SIDRASIDRA
SimTrafficSimTraffic
• Trafficware, USA
• Stochastic simulation model
• Uses Synchro for data input
• Driver behavior and vehicle characteristics
• Can change headway factors to calibrate to local conditions
• Trafficware, USA
• Stochastic simulation model
• Uses Synchro for data input
• Driver behavior and vehicle characteristics
• Can change headway factors to calibrate to local conditions
SimTrafficSimTraffic
ParamicsParamics
• Quadstone, UK
• Stochastic simulation model
• Driver behavior and vehicle characteristics
• Link/node network structure
• Automatically creates roundabout
• Lane change animation is unrealistic
• Quadstone, UK
• Stochastic simulation model
• Driver behavior and vehicle characteristics
• Link/node network structure
• Automatically creates roundabout
• Lane change animation is unrealistic
ParamicsParamics
VISSIMVISSIM
• PTV, Germany
• Stochastic simulation model
• 3D animation features
• Link/connector network structure
• Specify gap acceptance parameters by lane for each approach
• PTV, Germany
• Stochastic simulation model
• 3D animation features
• Link/connector network structure
• Specify gap acceptance parameters by lane for each approach
VISSIMVISSIM
Simulation LimitationsSimulation Limitations
• Too many parameters can be changed that affect results
• Some view simulation as a methodology to “prove” a predetermined result
• Many agencies/companies do not have the expertise to review simulation models
• Too many parameters can be changed that affect results
• Some view simulation as a methodology to “prove” a predetermined result
• Many agencies/companies do not have the expertise to review simulation models
Review of MethodsReview of Methods
• FHWA & RODEL– Based on British regression equations– Gap acceptance & lane configuration are not
addressed in the calculation– Very easy to use
• SIDRA & SimTraffic– Allow calibration of gap acceptance parameters
to local conditions– Easy to use
• Paramics & VISSIM– Most flexible in modeling driver behavior– More difficult to use as there are more
parameters affecting driver behavior
• FHWA & RODEL– Based on British regression equations– Gap acceptance & lane configuration are not
addressed in the calculation– Very easy to use
• SIDRA & SimTraffic– Allow calibration of gap acceptance parameters
to local conditions– Easy to use
• Paramics & VISSIM– Most flexible in modeling driver behavior– More difficult to use as there are more
parameters affecting driver behavior
Case Study #1 – Chico, CACase Study #1 – Chico, CA
• Widening of SR 32 in Chico, CA
• Two-lane rural highway with access control
• Design Year (2030) PM Peak Hour
• Project considered roundabouts at the 4 study intersections
• Widening of SR 32 in Chico, CA
• Two-lane rural highway with access control
• Design Year (2030) PM Peak Hour
• Project considered roundabouts at the 4 study intersections
Proposed DesignProposed Design
Source: Mark Thomas & Co.
RODEL Results: LOS ARODEL Results: LOS A
SIDRA Results: LOS CSIDRA Results: LOS C
VISSIM Results: LOS FVISSIM Results: LOS F
FHWA GuidelinesFHWA Guidelines
• ADT on SR 32 & Bruce Rd at the limit– Daily volumes on SR 32 are above 40,000
vpd with high left-turn percentages
• Peak-hour volumes exceed entry & circulatory volume capacity– Entry + circulatory flow ~ 2,500 vph
• Both indicate that the roundabout should be at or over capacity
• ADT on SR 32 & Bruce Rd at the limit– Daily volumes on SR 32 are above 40,000
vpd with high left-turn percentages
• Peak-hour volumes exceed entry & circulatory volume capacity– Entry + circulatory flow ~ 2,500 vph
• Both indicate that the roundabout should be at or over capacity
Review of RODEL ResultsReview of RODEL Results
• 20% increase in volume yields LOS F
• RODEL manual does not identify the upper limit of the empirical data
• RODEL does not account for right-turn delay even if vehicle queues block access to bypass lanes
• RODEL does not consider the capacity of the circulatory roadway
• 20% increase in volume yields LOS F
• RODEL manual does not identify the upper limit of the empirical data
• RODEL does not account for right-turn delay even if vehicle queues block access to bypass lanes
• RODEL does not consider the capacity of the circulatory roadway
Review of SIDRA ResultsReview of SIDRA Results
V/C Ratios on all approaches exceed 0.85
95th percentile queue is 883 feet
Review of VISSIM ResultsReview of VISSIM Results
Insufficient Circulatory Capacity
Blocked Right-turn Bypass Lanes
Case Study #2 – Reno, NVCase Study #2 – Reno, NV
• Initial study performed using RODEL – Volumes were 40% lower, Result = LOS A
• Asked by local agency to verify results• Comprehensive traffic analysis was
performed using Vissim• Volumes analyzed represent 20-year horizon
PM peak hour• Analysis compared signal and roundabout
• Initial study performed using RODEL – Volumes were 40% lower, Result = LOS A
• Asked by local agency to verify results• Comprehensive traffic analysis was
performed using Vissim• Volumes analyzed represent 20-year horizon
PM peak hour• Analysis compared signal and roundabout
Study AreaStudy Area
Proposed Roundabout Location
Proposed Design PlanProposed Design Plan
2-lane section matches existing roadway
configuration
Proposed Design ResultsProposed Design Results
Southbound queue as long as existing queue
with all-way-stop
Northbound vehicles will experience long
queues and delay
Modified Design PlanModified Design Plan
SB Kietzke Ln
Neil Rd Between Kietzke Ln and US 395 SB Ramps
3-lane section allows both southbound lanes on
Kietzke Ln to enter freeway
Modified Design ResultsModified Design ResultsMaximum Queue Length
Approach Length (feet)
WB Neil Road 535
SB Kietzke Ln (left-turn) 270
EB Del Monte Ln 160
NB Kietzke Ln (through) 240
NB Kietzke Ln (right) 225
Level of Service
Intersection Delay LOS
US 395 NB Ramps / Neil Rd 42 D
US 395 SB Ramps / Neil Rd 25 C
Kietzke Ln / Neil Rd 10 A
SB Neil Rd at Kietzke Ln
NB Neil Rd at Kietzke Ln
Modified Design ResultsModified Design Results
Parting ThoughtsParting Thoughts
• Similar to signalized intersection analysis, there is no “best” methodology
• Methodology should be dependant on the situation
• Concepts in the FHWA Simulation Guidelines & HCM also hold true in identifying whether roundabouts should be simulated
• Similar to signalized intersection analysis, there is no “best” methodology
• Methodology should be dependant on the situation
• Concepts in the FHWA Simulation Guidelines & HCM also hold true in identifying whether roundabouts should be simulated
More InformationMore Information
• Roundabouts: An Informational Guide (FHWA, 2000)– New edition due in 2009 or 2010
• TRB National Roundabout Conference – 2005 (Vail, CO)– 2008 (Kansas City, MO)
• ITE Conferences
• DOT Guidance – CA, FL, NY, WI, etc.
• Roundabouts: An Informational Guide (FHWA, 2000)– New edition due in 2009 or 2010
• TRB National Roundabout Conference – 2005 (Vail, CO)– 2008 (Kansas City, MO)
• ITE Conferences
• DOT Guidance – CA, FL, NY, WI, etc.
Questions?Questions?