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

2. Ourston Roundabout Engineeringwww.ourston.com 1.What constitutes non-conformance of a (large) circular intersection? 2.What are operating conditions are essential? 3.Several examples Outline 2

3. Ourston Roundabout Engineeringwww.ourston.com What do these video depictions have in common? 3

4. Ourston Roundabout Engineeringwww.ourston.com 4 What do these video depictions have in common?

5. Ourston Roundabout Engineeringwww.ourston.com More Subtle Issues 5

6. Ourston Roundabout Engineeringwww.ourston.com Weaving in a non-conforming circle ``` `` Long parallel left curve between entry and exit 6

7. Ourston Roundabout Engineeringwww.ourston.com 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. Ourston Roundabout Engineeringwww.ourston.com Classic Rotary Designs: “Bigger was Better” Bluebonnet Circle, Fort Worth Diameter: ~450’ 8

9. Ourston Roundabout Engineeringwww.ourston.com Roundabout Research History United States France United Kingdom Australia Gap EmpiricalWeaving or First-InGap19661980 Gap & Empirical Weaving Vague Priority Rules Empirical1984 9 Rotaries, Large Circles (Weaving or First-In) Compact Circles (Yield, deflection, flare) Safety Emphasis Balance of Safety and Capacity Priority Rules Change in the U.K. 1990

10. Ourston Roundabout Engineeringwww.ourston.com Research revealed deeper underlying problems 1.Incorrect geometry –Undeflected entry paths –Circle size –Alignment of arms 2.Ineffective geometry –Uneven lane use/balance –Unnatural entry and/or exit paths 3.Incorrect Stripes 4.Sight distance deficiencies

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

12. Ourston Roundabout Engineeringwww.ourston.com 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. Ourston Roundabout Engineeringwww.ourston.com Roundabout collisions = low severity (failure to yield) 13

14. Ourston Roundabout Engineeringwww.ourston.com Coordination of Geometry and Lane Designation 14

15. Ourston Roundabout Engineeringwww.ourston.com Lane Choice Before Entry 15

16. Ourston Roundabout Engineeringwww.ourston.com Roundabout collisions = low severity (incorrect lane choice) 16

17. Ourston Roundabout Engineeringwww.ourston.com 17 Still… Common Operational Problems With Modern Roundabouts PROBLEM PERCENTAGE Signs 15% New Markings 9% Cyclists 7% Inadequate Deflection7% 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. Ourston Roundabout Engineeringwww.ourston.com Case Studies 18 Solutions range from markings and signs only to comprehensive reconstruction.

19. Ourston Roundabout Engineeringwww.ourston.com 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. Ourston Roundabout Engineeringwww.ourston.com Rehabilitation Site: Armdale Rotary, Halifax, NS

21. Ourston Roundabout Engineeringwww.ourston.com 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. Ourston Roundabout Engineeringwww.ourston.com 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. Ourston Roundabout Engineeringwww.ourston.com Conditions Before

24. Ourston Roundabout Engineeringwww.ourston.com Circle Locked Before Rule Change

25. Ourston Roundabout Engineeringwww.ourston.com Previous Partial Closure of the Circulatory (…for over a decade)

26. Ourston Roundabout Engineeringwww.ourston.com Previous Partial Signalization “Yield then proceed”

27. Ourston Roundabout Engineeringwww.ourston.com New Priority Rules (2006) = Unlocked Circle

28. Ourston Roundabout Engineeringwww.ourston.com 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. Ourston Roundabout Engineeringwww.ourston.com Historical Lane Use Habits… Education?

30. Ourston Roundabout Engineeringwww.ourston.com Shortly before full opening…

31. Ourston Roundabout Engineeringwww.ourston.com 31 Shortly before full opening…

32. Ourston Roundabout Engineeringwww.ourston.com Revised Signs Old – pull thru styleNew Diagrammatic Consecutive let turns…

33. Ourston Roundabout Engineeringwww.ourston.com 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. Ourston Roundabout Engineeringwww.ourston.com 34 Cony Rotary, Augusta, ME

35. Ourston Roundabout Engineeringwww.ourston.com Cony Rotary, Augusta, ME 35

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

37. Ourston Roundabout Engineeringwww.ourston.com Long Beach Circle 19922010? Still 5,300veh./hour at LOS A

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