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Roundabouts 101 Victor Salemann, PE David Evans and Associates.

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Presentation on theme: "Roundabouts 101 Victor Salemann, PE David Evans and Associates."— Presentation transcript:

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 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 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

20 Sample Design Visualizations Existing all-way stopProposed Roundabout

21 Sample Design Visualizations Existing t-intersectionProposed Roundabout

22 Sample Design Visualizations Existing traffic signalProposed Roundabout

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

24 A Recipe for Disaster Using thisWithout this Image source willamette.edu

25 Local Conditions Matter When using thisBe 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 Slow entry speeds Consistent speeds through the roundabout The appropriate number of lanes Smooth channelization Appropriate sight distance and visibility Some conflicting objectives Adequate accommodation for all design vehicles A design that meets the needs of pedestrians and bicyclists

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

33 Don’t Ignore Trucks Right turns vs. left turnsConsequences 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 flexibleBut 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 ConsiderationsUnderstand the Failure Mode Focus on corridor operation

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

37 Corridors Corridor ConsiderationsUnderstand 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 HAWKRRFB

42 Rural Roundabout Design Grandview/Blaine Road Whatcom County, WA

43 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 Design Grandview/Blaine Road Whatcom County, WA High Speed Entry 50 mph approach speed from east and west Extended splitter islands encourage early braking

45 Rural Roundabout Design Grandview/Blaine Road Whatcom 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 Design Grandview/Blaine Road Whatcom County, WA No Urbanization Low pedestrian demand – crosswalks not provided Moderate bicycle demand Moderate agricultural vehicles WSDOT design vehicles

47 Rural Roundabout Design Grandview/Blaine Road Whatcom County, WA Wetlands Natural and constructed wetlands on three quadrants Reverse approach curves minimized to reduce impacts Linear stormwater treatment utilized

48 Rural Roundabout Design Grandview/Blaine Road Whatcom County, WA BP Refinery Roundabout selected for safety benefits 800 vph volumes at shift changes required bypass lane Bypass lane accommodates super loads every 3-5 years All curb sections are mountable

49 Drought Tolerant Landscaping Grandview/Blaine Road Whatcom County, WA

50 How to Learn More Go watch a roundabout 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 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?

51 Conclusions Roundabout design is challenging The public is typically doubtful at first Bad design assumptions result in problems The FHWA Roundabout Guide really is more of a guide than a code Roundabouts can be design for rural locations at a reasonable cost Be aware of new Federal ADA requirements Corridors require additional considerations Be observant during construction Use a trained staff or a qualified local (regional) consultant

52 Questions? Victor Salemann, PE


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