Roundabout capacity analysis
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NEW YORK STATE DEPARTMENT OF TRANSPORTATION. Roundabout Capacity Analysis. My, not necessarily NYSDOT’s, opinion of most of the commonly used programs throughout the US from an actual user and reviewer perspective. Roundabout Capacity Software. SIDRA Intersection

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Roundabout capacity analysis

NEW YORK STATE DEPARTMENT OF TRANSPORTATION

Roundabout Capacity Analysis


Roundabout capacity analysis

My, not necessarily NYSDOT’s, opinion of most of the commonly used programs throughout the US from an actual user and reviewer perspective


Roundabout capacity analysis

Roundabout Capacity Software

  • SIDRA Intersection

  • RODEL / ARCADY

  • SYNCHRO 6, 7

  • Results of NCHRP 3-65, Report 572

  • VISSIM

  • PARAMICS


Roundabout capacity analysis

Two Types of Capacity Prediction Models

Gap Theory

  • SIDRA, SYNCHRO, VISSIM, Paramics

    • Theoretical Capacity

    • “Seeing is believing”

Empirical

  • RODEL or ARCADY

    • Based on field measurements, not theory

    • Capacity measured during “at capacity” operation in U.K.

Note: They can give very different results


Single lane fhwa study

Single Lane FHWA Study


Dual 2 lane fhwa study programs still do not agree

Dual (2) Lane FHWA Study – programs still do not agree


Roundabout capacity analysis

SIDRA

  • Developed in Australia

  • Gap theory analysis

  • Geometric parameters partially considered

  • Used by about 80% of the country

  • Does signals, most other intersections also

  • Calculates emissions – CMAQ money… 


Roundabout capacity analysis

SIDRA – pre-Version 3

  • Concerns over high capacity predictions with low circulating flows can be resolved – use 1.2 Environment Factor:


Roundabout capacity analysis

SIDRA USER

  • Quite user friendly – quick & easy to follow

  • Movement displays are nice for design reports

  • Data easily extracted from results

    SIDRA REVIEWER

  • Lots of output to review

  • Quite a few “defaults” can be altered to manipulate results

  • Really want actual file

  • Some user error is possible


Roundabout capacity analysis

SIDRA – Future Desires

  • To go froma display thatgives general movementdata:

    to a display that gives conflict totals per lane crossing locations or at least per lane on approach & circulating

  • Also, export displays


Roundabout capacity analysis

RODEL – similar to ARCADY

  • Developed in Great Britain

  • Empirical analysis

  • Geometric parameters considered

  • Used by about 30% of the country

  • D.O.S. based

  • Metric Only

  • Only models roundabouts

  • RODEL 2 (Arcady 7) is here…  for info see:

  • http://teachamerica.com/RAB08/RAB08S5BJohnson/index.htm


Roundabout capacity analysis

Why Roundabouts Re-emerged

  • Research on 35 geometric variations

  • Many roundabouts were rehabilitated and new sites were considered

  • Follow up study confirmed the capacity prediction equations were valid

TRL study test track (U.K.) - 1968


Roundabout capacity analysis

Empirical Model

  • Strongly relates capacity to detailed geometry

  • Accidents also directly related to geometry

  • Great tool for the design engineer

  • Helps find the “optimum” geometry


Roundabout capacity analysis

Capacity of an Approach – not lane by lane… 


Roundabout capacity analysis

Geometric Parameters


Roundabout capacity analysis

Effective Geometric Parameters

V =Approach Roadway Width

E = Entry Width

L’ = Effective Flare Length

D = Inscribed Circle Diameter

R = Entry Radius

Phi = Entry angle


Roundabout capacity analysis

RODEL = ROundabout DELay


Roundabout capacity analysis

RODEL USER

  • User friendly – but need to understand design

  • Instantly see results from geometric revisions

  • 1 input screen is all you need

    RODEL REVIEWER

  • 1 screen capture is all you need

  • No real “defaults” that can be altered to manipulate results

  • Can’t really go from RODEL to CAD file

  • User error is common

  • Really need to understand design


Roundabout capacity analysis

RODEL – Future Desires

  • To be able to analyze lane by lane – unbalanced lane use, assumption of circulating lanes, and compounding lefts cause questionable results currently


Roundabout capacity analysis

RODEL = ROundabout DELay

Remember leg from the north…


Roundabout capacity analysis

RODEL – Future Desires

  • To have better controlover input widths – a few organizationshave already developed “default” geometric inputs


Roundabout capacity analysis

SYNCHRO / SimTraffic 6, 7

  • Uses HCM 2000 equations

  • Geometric parameters not considered

  • Compared to real sites?

  • Will only analyze single lane roundabouts

    • SIM Traffic will simulate up to 4 laners

  • Doesn’t calculate L.O.S. based on delay

  • Will do most other intersections


Roundabout capacity analysis

SimTraffic 6 clip – Multi-Lane Roundabout Think about which lanes go where…


Roundabout capacity analysis

SimTraffic 7 clip – Multi-Lane Roundabout3D simulation goes a long way with convincing decision makers & John Q. Public


Roundabout capacity analysis

SYNCHRO / SimTraffic USER

  • User friendly for single laners

  • Inputs very similar to that of other intersections

  • Difficult to control lane use within roundabout

    SYNCHRO / SimTraffic REVIEWER

  • Lots of data in output – real worth???

  • Single laners – you need to watch video

  • Multi-Laners – really no good way to review since lane use within roundabout doesn’t follow typical designs


Roundabout capacity analysis

SYNCHRO / SimTraffic – Future Desires

  • To have LOS based on delay – hopefully the formulas from Report 572 will be incorporated. Currently, good designs get poor LOS because they use 60 to 80% of their capacity. Over-designs are rewarded with better LOS based on ICU…

  • WHAT IS ICU?

  • WHAT DOES “#” MEAN?

  • WHAT DOES “~” MEAN?

  • If you use Synchro to simulate multi-laners please make sure you take the time to read:

  • http://www.trafficware.com/assets/pdfs/Multi-lane%20Roundabouts%20Supplement.pdf


Roundabout capacity analysis

NCHRP 3-65 – Report 572

  • National Cooperative Highway Research Program – Applying Roundabouts in the United States

  • Initial project is done, see Report 572

  • FHWA wanted “U.S. program”

  • Equation is best fit to existing US conditions

  • Multi-Lane analysis is based on critical lane

  • Currently working on the next FHWA Roundabout Guide


Roundabout capacity analysis

NCHRP 3-65 – Report 572 – Single Laners


Roundabout capacity analysis

NCHRP 3-65 – Report 572 – Delay & Queue


Roundabout capacity analysis

NCHRP 3-65 – Report 572 – Two Laners


Roundabout capacity analysis

NCHRP 3-65 - Report 572 USER

  • User friendly – if you can work a calculator

  • Easy to determine if capacity is there

  • Delay & Queues require a little more time

    NCHRP 3-65 - Report 572 REVIEWER

  • Need to check lane assignments

  • No “defaults” that can be altered to manipulate results

  • User error is eliminated

  • Designer error can still influence results


Roundabout capacity analysis

NCHRP 3-65 – Report 572 – Future Desires

  • To have a more user-friendly platform

  • To be able to account for unbalanced circulating flows

  • To be able to analyze each approach lane separately

  • To be able to apply to 3 lane roundabouts


Roundabout capacity analysis

Simulation Programs

  • Not typically used for roundabout design – are being used to visually check predictions – NYSDOT wants to see VISSIM

  • Great tools for Public Info Meetings

  • Able to show network impacts

  • Visually displays improved performance provided by roundabouts

  • VISSIM seems to be more common choice

  • Paramics is comparable but more expensive


Roundabout capacity analysis

VISSIM

  • Developed in Germany

  • Gap Based – not geometric specific

  • Great tool for Public Info Meetings

  • Able to show network impacts

  • Can visualize impacts from signalized pedestrian crossings… 

  • Does nearly any roadway & intersection configuration possible: like cfi, ddi, spui …


Roundabout capacity analysis

VISSIM – showing signalized ped crossings


Roundabout capacity analysis

VISSIM Clip – using Level 1 - $2000


Roundabout capacity analysis

VISSIM Clip – shows overall improvements


Roundabout capacity analysis

VISSIM Clip – using Level 2 - $3000 more


Roundabout capacity analysis

Using 3D Studio Max with VISSIM

This video comes from a project in Carmel, Indiana. You might want to put in your paperwork now for the 2011 National Roundabout Conference in Carmel – May 11-13th or so.


Roundabout capacity analysis

VISSIM USER

  • More time consuming – unless using templates

  • Truck/car interaction can be challenging

  • Excellent control of lane use within roundabout

    VISSIM REVIEWER

  • Output Data isn’t as refined as other programs

  • Time Consuming – you need to watch the video

  • Constant updates – especially when dealing with DOT software installation procedures


Roundabout capacity analysis

VISSIM – Future Desires

  • To not have vehicles be able to cross through each other – conflict areas???

  • NOTE: Make sure you never have vehicles crossing in your presentation! We do not want to go in front of the public with an actual VISSIM file – video clips are much safer.

  • Standardized “appealing” Output Format


Roundabout capacity analysis

PARAMICS

  • Developed in Scotland

  • Does have actual roundabout “node”

  • Roundabout “node” does have limitations

  • Great tool for Public Info Meetings

  • Origin-Destination based routing

  • A little bit more expensive than the other programs

  • Steep learning curve


Roundabout capacity analysis

Paramics Clip – costs around $12,000


Roundabout capacity analysis

Paramics Clip


Roundabout capacity analysis

PARAMICS – arrows show allowed movements


Roundabout capacity analysis

PARAMICS – like VISSIM – will demonstrate “Too Fast Too Furious” driving behavior


Roundabout capacity analysis

PARAMICS USER – years ago anyway

  • More time consuming – especially with non-traditional lane use within roundabout

  • Truck/car interaction can be challenging

  • Decent control of lane use within roundabout

    PARAMICS REVIEWER

  • Output Data isn’t as refined as other programs

  • Time Consuming – you need to watch the video


Roundabout capacity analysis

PARAMICS – Future Desires

  • To not have vehicles be able to cross through each other – does not go over well with less than enthused audience

  • Standardized “appealing” Output Format

  • Large Vehicle tracking more realistic

  • Better lane control at approach and within roundabout – sometimes vehicles will realize at the yield line that they needed to be in other lane – could be realistic though… 


Roundabout capacity analysis

Roundabout Capacity Software

  • SIDRA Intersection

  • RODEL / ARCADY

  • SYNCHRO 6, 7

  • Results of NCHRP 3-65, Report 572

  • VISSIM

  • PARAMICS

  • ANY OTHERS???

  • Which one (or more) to choose???

  • The next few slides show a “simplified” method used at NYSDOT


Roundabout capacity analysis

The Real Limitation to the Capacity of a Roundaboutis at the Yield Line

The availability of usable gaps in the circulatory roadway traffic for approaching vehicles trying to enter the roundabout is what truly limits the roundabouts capacity…

THE ACTUAL DESIGN SPECS DON’T REALLY MATTER AS LONG AS IT IS A GOOD DESIGN… 


Roundabout capacity analysis

Quick Capacity “Guesstimate” for Single Laner

  • 0 - 750LOS A

  • 750 - 850LOS A / B

  • 850 - 950LOS B / C

  • 950 - 1050LOS C / D

  • 1050 - 1150LOS D / E

  • 1150 - 1400LOS E / F

  • DON’T EXCEED 1400 VPH AT THE CONFLICT POINT FOR A 1 LANER


Roundabout capacity analysis

Capacity Limits -Not Lane by Lane

If sum is 0 – 1,000 then

Single lane works

If sum is 1,000 – 1,300 then

Single lane might work

If sum is 1,300 – 1,800 then

2 laner works

If sum is1,800 – 2,200 then

2 laner might work

If sum is 2,200 – 2,900

3 laner might work


Roundabout capacity analysis

Capacity Limits –Still want to Check Lane by Lane – now 900 vphpl is limit

The 1,000 rule of thumb drops to 900 because entering vehicles need to find acceptable gaps in both circulating lanes at once – some gaps in the outer lane will be eliminated by the vehicles circulating in the inner lane….

Potential Capacity Problems


The nysdot roundabout design unit would like to thank everyone for their attention this morning

The NYSDOTRoundabout Design Unit would like to thank everyone for their attention this morning…


Nysdot roundabout design unit contact information

NYSDOT Roundabout Design UnitContact Information

Howard McCulloch, Richard Schell, PE

Michael Houlihan, Greg Bailey

and Tom Kligerman, PE

Roundabout Design Unit

50 Wolf Road, POD 24

Albany, New York 12232

Tel: (518) 485-7503

Fax: (518) 457-2916

E-mail: [email protected]


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