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?