Roundabouts 101 Victor Salemann, PE David Evans and Associates

1. Roundabouts 101 Victor Salemann, PE David Evans and Associates

2. Presentation Outline • Roundabout Basics • Classes of Roundabouts • Roundabout LOS • Public Perception • Public Involvement • Roundabout Design Challenges • The Best Start to Good Roundabout Design • Getting the Details Right • Common Design Problems • Field Modifications • New ADA Requirements • Rural Roundabout Design • How to Learn More • Conclusions • Questions

3. Roundabout basics

4. All circular intersections are not roundabouts

5. Traffic Calming Circle

6. DuPont Traffic Circle

7. East Coast Rotaries

8. There are several “classes” of roundabouts

9. Mini Roundabout

10. Urban Compact Roundabout

11. Urban Single Lane Roundabout

12. Rural Single Lane Roundabout

13. Urban Multi-lane Roundabout

14. Suburban Multi-lane Roundabout

15. Rural Multi-Lane Roundabout

16. Roundabout LOS Signals and Roundabouts an Apples to Oranges Comparison

17. Two Different LOS Standards Signalized vs. roundabout LOS 50 seconds of delay is LOS D for a signal Is LOS F for a roundabout The delay comparison is still valid 50 seconds is 50 seconds Present findings in delay vs. LOS Compare LOS/Delay by approach

18. Public Perception Often Negative… Some reasons Bad experience with traffic calming circles west coast Bad experience with rotaries east coast No experience with roundabouts at all first roundabout Photo by Sam Hodgson

19. Public Involvement Strategies First Roundabout Subsequent Roundabouts Less contentious Often desired Opposition typically drops to 15% Problem identification still important Matchbox scale not as helpful Design visualizations still valuable One-on-one with adjacent property owners still a must • Expect opposition • Typically 41% Against • Make sure you have a problem to solve • Use design visualizations • Use “matchbox” scale plans for hands on interaction • Refer to other local projects they can visit • One-on-one with adjacent property owners

20. Sample Design Visualizations Existing all-way stop Proposed Roundabout

21. Sample Design Visualizations Existing t-intersection Proposed Roundabout

22. Sample Design Visualizations Existing traffic signal Proposed Roundabout

23. Roundabout Design Challenges • Roundabouts require more information than signals to design well • Design resources are limited • FHWA Roundabout Guide (2nd Edition) • State DOT Design Manuals • European and Australian Guides • Automated design solutions

24. A Recipe for Disaster Using this Without this Image source willamette.edu

25. Local Conditions Matter When using this Be aware of Sources of data in the guide Locations of reference studies Climate Vehicle sizes Familiarly with roundabouts Local context of your project Climate Vehicle sizes Familiarly with roundabouts

26. Design Objectives Good roundabout design Some conflicting objectives Adequate accommodation for all design vehicles A design that meets the needs of pedestrians and bicyclists • Slow entry speeds • Consistent speeds through the roundabout • The appropriate number of lanes • Smooth channelization • Appropriate sight distance and visibility

27. The best start to a good roundabout design

28. Offset Left Entry Design

29. Why Offset Left? • Reduces Entry Speed • Increases Exit Speed • Results in Good Speed Consistency • Accommodates Larger Trucks in the Same ICD • Eliminates RLR • Improves Crosswalk Visibility • Easier to Maintain

30. R Values with Offset Left Design

31. A Word about R values Focusing on fastest paths Can lead to bad design Ignores striping It is a design check Provides design guidance Does not ensure good design Striped paths can be very different Resulting actual speeds can be inconsistent

32. Getting the Details Right Basics Watch for… PM peak vs. AM Peak Driveways, delivery access Oversize loads even if infrequent Plowing and snow storage Valves in circulating lanes • Traffic data • Local access needs • Freight routes • especially on highways • Climate considerations • Utility considerations

33. Don’t Ignore Trucks Right turns vs. left turns Consequences Reduced intersection capacity Pedestrian risks Sidewalk encroachments Vehicle risks Crashes Vehicle damage Facility risks Curb/landscape damage Sign/illumination damage

34. Roundabouts at the Limit Very flexible But not very adjustable How much information would you want if you were asked to design a fixed time traffic signal that would not be changed for 20 years? Roundabouts are very forgiving until they are saturated

35. Corridor Applications Corridor Considerations Understand the Failure Mode Focus on corridor operation

36. Corridors Corridor Considerations Understand the Failure Mode Focus on corridor operation Evaluate queuing at critical legs Avoid internal gridlock

37. Corridors Corridor Considerations Understand the Failure Mode Focus on corridor operation Evaluate queuing at all legs Avoid internal gridlock Use corridor entry points as meters by controlling capacity

38. Common Design Problems • Exit geometry that is too constrained • Multi-lane exits (striping and signing) • Bypass lanes without receiving lanes • Complex grading and drainage • ADA compliance • Illumination • Automated Design Solutions

39. Owner Modifications Notice Anything? Owners looking to cut costs often make changes with significant impacts Communicate key design features to owners before construction Get out to the field during construction Photo by Shannon at Sequim Daily Photo

40. New ADA Requirements

41. Signalized Pedestrian Crossings for Multi-lane Roundabouts HAWK RRFB

42. Rural Roundabout DesignGrandview/Blaine RoadWhatcom County, WA

43. Rural Roundabout DesignGrandview/Blaine RoadWhatcom County, WA Project Setting • Intersection of a rural two lane highway (SR 548) and two lane county road • Shoulder section on all approaches • No urbanization anticipated • Wetlands on three quadrants of the intersection • BP Refinery accessing south leg

44. Rural Roundabout DesignGrandview/Blaine RoadWhatcom County, WA High Speed Entry • 50 mph approach speed from east and west • Extended splitter islands encourage early braking

45. Rural Roundabout DesignGrandview/Blaine RoadWhatcom County, WA Shoulder Section • Consistent with approach roads • Simplified drainage • Reduced costs significantly • Not addressed in FHWA Guide • Speeds within FHWA guide criteria

46. Rural Roundabout DesignGrandview/Blaine RoadWhatcom County, WA No Urbanization • Low pedestrian demand – crosswalks not provided • Moderate bicycle demand • Moderate agricultural vehicles • WSDOT design vehicles

47. Rural Roundabout DesignGrandview/Blaine RoadWhatcom County, WA Wetlands • Natural and constructed wetlands on three quadrants • Reverse approach curves minimized to reduce impacts • Linear stormwater treatment utilized

48. Rural Roundabout DesignGrandview/Blaine RoadWhatcom County, WA BP Refinery • Roundabout selected for safety benefits • 800 vphvolumes at shift changes required bypass lane • Bypass lane accommodates super loads every 3-5 years • All curb sections are mountable

49. Drought Tolerant LandscapingGrandview/Blaine RoadWhatcom County, WA

50. How to Learn More Go watch a roundabout Go drive a roundabout Drive lots of them Try all the movements Were they intuitive? Did you really need the signs and stripes? Observe your speeds Comfortable? • Watch lots of them • How do drivers behave? • How do different vehicles use it? • How do pedestrians use it? • How do bicyclists use it? • Look for signs of damage to curbs, landscaping, or signs