Converting Non-Conforming Circles to Roundabouts

1. Converting Non-Conforming Circlesto Roundabouts Mark Lenters Ourston Roundabout Engg. mlenters@ourston.com

2. Outline • What constitutes non-conformance of a (large) circular intersection? • What are operating conditions are essential? • Several examples

3. What do these video depictions have in common?

4. What do these video depictions have in common?

5. More Subtle Issues

6. Weaving in a non-conforming circle `` ``` Long parallel left curve between entry and exit

7. What are common non-conformance attributes? Unclear priority rules – first in, circle traffic yielding Unusually high entry speeds Safety performance deficiencies – rear ends at entry, sideswipes circulating and exiting Lane imbalance on entries Incorrect lane use on the circulatory - and notable conflict patterns, e.g. incorrect lefts Capacity limitation, but not always – some are very efficient even though they’re crash prone.

8. Classic Rotary Designs:“Bigger was Better” Bluebonnet Circle, Fort WorthDiameter: ~450’ 8

9. Roundabout Research History Weaving Gap & Empirical Vague Priority Rules 1984 Empirical Gap Priority Rules Change in the U.K. United States 1990 France Safety Emphasis United Kingdom Balance of Safety and Capacity Weaving or First-In 1966 Gap 1980 Empirical Compact Circles (Yield, deflection, flare) Rotaries, Large Circles (Weaving or First-In) Australia

10. Research revealed deeper underlying problems • Incorrect geometry • Undeflected entry paths • Circle size • Alignment of arms • Ineffective geometry • Uneven lane use/balance • Unnatural entry and/or exit paths • Incorrect Stripes • Sight distance deficiencies

11. How Do Modern Roundabouts Operate? ` ` ` ` ` ` ` ` ` Conflict space is compact and well defined No parallel left curve between entry and exit ` ` ` ` ` ` ` ` Slowed & natural entry paths

12. What Defines a Roundabout? Yield at Entry – keeps traffic moving. No weaving • Deflection – slows traffic. Improves safety. • Flare – provides high capacity in a compact space. 12

13. Roundabout collisions = low severity (failure to yield)

14. Coordination of Geometry and Lane Designation 14

15. Lane Choice Before Entry 15

16. Roundabout collisions = low severity (incorrect lane choice)

17. Still… Common Operational Problems With Modern Roundabouts PROBLEMPERCENTAGE Signs 15% New Markings 9% Cyclists 7% Inadequate Deflection 7% Delineation 6% Lane Configuration 6% Pedestrians 6% Visibility 6% Sight Lines 6% Pole Location 5% Lighting 5% Traffic Design Group for Transfund New Zealand, The Ins and Outs of Roundabouts - Safety Auditors’ Perspective, 2002

18. Case Studies • Solutions range from markings and signs only to comprehensive reconstruction.

19. Common Observed Deficiencies: Incorrect Design Consequences: Violation of circulating priority Incorrect lane choice – exit crashes (sideswipe) Sudden lane changes Weaving in the circle Navigational and way-finding errors Corrections Include: Lane arrows on circulatory opposite splitter islands Use lane designation arrows on approaches Use of exit stripes Use of spiral marking Design the geometry & markings together

20. Rehabilitation Site:Armdale Rotary, Halifax, NS

21. Conditions Before 2007 Alterations • 238 reported collisions (5 yrs.) • 48 collisions per year • 2.60 collisions per million vehicles per year • Hourly volume = 5,500 veh. • 38 injury related (16%) • Injury Freq. = 7.6/yr is significantly higher than average frequency (3 to 6) for 4 leg U.K. roundabouts

22. Sequence of Events 2005 roundabout priority rules enacted Initial study of the rotary 2006 Roundabout rules enforced at the Armdale (signs, enforcement and education) Follow-up study to refine geometry 2007 Major geometric changes with signs and stripes Follow-up study planned for June 2009 Contingency for metering signal underground installed (not recommended in the study)

23. Conditions Before

24. Circle Locked Before Rule Change

25. Previous Partial Closure of the Circulatory (…for over a decade)

26. Previous Partial Signalization “Yield then proceed”

27. New Priority Rules (2006) = Unlocked Circle

28. Alteration Techniques: • Conventional in-service review process • Relating accident/conflict problems to principles of operation led to the solution. • Observations + traffic flow patterns + empirical geometry relationships = improvements to geometry, markings and signs • Non-U.S. models used for subtle geometric adjustments to improve capacity and safety. • Empirical** design principles used to develop safety and capacity improvements **Traffic Capacity of Roundabouts, R.M. Kimbers, LR942, TRL 1980 **Accidents at Four Arm Roundabouts, Maycock and Hall, LR1120, TRL, 1984

29. Historical Lane Use Habits… Education?

30. Shortly before full opening…

31. Shortly before full opening…

32. Revised Signs Old – pull thru style New Diagrammatic Consecutive let turns…

33. Early Results (2 years after) Reduced congestion morning and evening peaks (one short flared entry (2-3)). Significant reduction in collisions and conflicts Lane discipline on the approaches and in the circulatory. Slower entry and circulating speeds Congestion moved into downstream road network as predicted

34. Cony Rotary, Augusta , ME

35. Cony Rotary, Augusta , ME

36. 1992 Improvements to Capacity and Safety Nonconforming Traffic Circle Becomes Modern Roundabout Leif Ourston, Presented to ITE 64th Annual Meeting, Dallas, TX, 10/94

37. Long Beach Circle 1992 2010? Still 5,300veh./hour at LOS A

38. Conclusions Roundabouts previously without possible relief can be modified using the U.K. empirical design principles with significant lasting collision reduction and congestion relief. The improvements demonstrate strong geometric sensitivity of parameters other than the number of lanes. The way the principles and predictive models can be applied to multi-lane/multi-leg roundabouts needs more attention in documented case studies and in U.S. guidelines.

39. Questions following part 2… Mark Lenters Ourston Roundabout Engg. mlenters@ourston.com 608-249-4545