Roundabout Capacity Analysis

1. 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. 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

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

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 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

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

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.) - 1968

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

17. RODEL = ROundabout DELay

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 controlover input widths – a few organizationshave 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 Roundabout3D simulation goes a long way with convincing decision makers & John Q. Public

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

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 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

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

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

37. VISSIM Clip – shows overall improvements

38. VISSIM Clip – using Level 2 - $3000 more

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.

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

44. Paramics Clip

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 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… 