1. Roundabout Capacity Analysis
NEW YORK STATE DEPARTMENT OF TRANSPORTATION
Roundabout Capacity Analysis

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

3. Roundabout Capacity Software
SIDRA Intersection
RODEL / ARCADY
SYNCHRO 6, 7
Results of NCHRP 3-65, Report 572
VISSIM
PARAMICS

4. Note: They can give very different results
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

5. Single Lane FHWA Study
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6. Dual (2) Lane FHWA Study – programs still do not agree
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7. 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… 

8. SIDRA – pre-Version 3
Concerns over high capacity predictions with low circulating flows can be resolved – use 1.2 Environment Factor:

9. 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

10. SIDRA – Future Desires
To go from a display that gives general movement data:
to a display that gives conflict totals per lane crossing locations or at least per lane on approach & circulating
Also, export displays

11. 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:

12. 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.)

13. 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

14. Capacity of an Approach – not lane by lane… 

15. Geometric Parameters

16. Effective Geometric Parameters
V = Approach Roadway Width
E = Entry Width
L’ = Effective Flare Length
D = Inscribed Circle Diameter
R = Entry Radius
Phi = Entry angle
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17. RODEL = ROundabout DELay
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18. 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

19. 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

20. RODEL = ROundabout DELay
Remember leg from the north…

21. RODEL – Future Desires
To have better control over input widths – a few organizations have already developed “default” geometric inputs

22. 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

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

24. SimTraffic 7 clip – Multi-Lane Roundabout 3D simulation goes a long way with convincing decision makers & John Q. Public
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25. 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

26. 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:

27. 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

28. NCHRP 3-65 – Report 572 – Single Laners

29. NCHRP 3-65 – Report 572 – Delay & Queue

30. NCHRP 3-65 – Report 572 – Two Laners

31. NCHRP 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 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

32. 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

33. 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
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34. 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 …

35. VISSIM – showing signalized ped crossings

36. VISSIM Clip – using Level 1 - $2000
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37. VISSIM Clip – shows overall improvements
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38. VISSIM Clip – using Level 2 - $3000 more
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39. 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.
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40. 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

41. 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

42. 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

43. Paramics Clip – costs around $12,000
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44. Paramics Clip
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45. PARAMICS – arrows show allowed movements

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

47. 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

48. 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… 

49. 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

50. The Real Limitation to the Capacity of a Roundabout is 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… 

51. Quick Capacity “Guesstimate” for Single Laner
LOS A
LOS A / B
LOS B / C
LOS C / D
LOS D / E
LOS E / F
DON’T EXCEED 1400 VPH AT THE CONFLICT POINT FOR A 1 LANER

52. 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

53. Potential Capacity Problems
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

54. The NYSDOT Roundabout Design Unit would like to thank everyone for their attention this morning…

55. NYSDOT Roundabout Design Unit Contact 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)
Fax: (518)