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February 10, 2015
FHWA Resource Center 1
Modern Roundabouts: Changing our Intersection LandscapeSouth Tahoe, CA • February 10, 2015
Hillary N. Isebrands, PE, PhDUSDOT ‐ FHWA Resource CenterSafety & Design Technical Service TeamLakewood, CO
Vail , CO Kings Beach, CA
Incline Village, NV
Source of Images: Isebrands, Google Earth, Isebrands
Topics for Discussion
» Intersection Safety Facts
» Roundabouts Facts & Characteristics
» Designing for All Users & Roadway Character
» Roundabout Examples
» Summary
» Questions/Discussion
Photo Source: Isebrands
February 10, 2015
FHWA Resource Center 2
Intersection Safety Facts
Source Isebrands, FHWA
» About half of all severe crashes occur at intersections
» 25% of all fatalities are at intersections» Angle crashes account for over 40% of fatal crashes at intersections
» Left turn crashes account for over 20% of fatal crashes at intersections
» Ped/Bike crashes account for 25% of fatal crashes at signalized intersections
FHWA Focused Approach to Safety
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» Increase awareness of intersections» Increase visibility of intersections and traffic control devices
» Improve the design of intersections to reduce conflicts
» Improve driver navigation to reduce confusion
» Improve the operations of intersections» Improve sight distance at intersections» Improve driver compliance with traffic control devices
Key Areas for Improving Intersection Safety
Source of Images: Google Earth
Middleton, ID
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Roundabout Facts & Characteristics
Source of Images: Google Earth
Roundabout Safety Experience
» Fatal and injury crashes reduced significantly
» The number of conflict points is ¼ of traditional intersection
» Changes in the types of crashes
» Slow speeds for all vehicles
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Pedestrians Roundabout Experience
» Low speeds (15‐25mph)
» Fewer conflict points (16 to 8 ped‐veh)
» Shorter crossing distances
» Cross only one direction of travel at a time
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Photo credits: Butzek
Source of Images: Seattle DOT and Asheville, NC
Asheville, NC
Physical Features of a Modern Roundabout
Pedestrian Crossing
Raised Central Island Counter‐clockwise
Circulatory Roadway
Deflected Entry Path with Yield control
Raised Splitter Island
Raised Truck Apron
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Not All Circular Intersections Are Roundabouts
Roundabouts
RotariesNeighborhoodtraffic circles
All circularintersections
Others
Neighborhood Traffic Circle
Image Source : FHWA/NCHRP 672
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FHWA Resource Center 7
Traffic Circle to Roundabout Retrofit
Smaller diameter ‐ 225 ft
Photo Source: NYSDOT
Large diameter (600 ft +)
Traffic Circle to Roundabout Retrofit
Source: Google Earth
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FHWA Resource Center 8
Designing for All Users & Roadway Character
Source of Images: Google Earth
Roundabout Guidance
» FHWA» Proven Safety Countermeasure (2008, 2012)» NCHRP 672 Roundabouts: An Informational Guide (2010)
» CalTrans» Highway Design Manual» Intersection Control Evaluation (ICE)Directive
» NVDOT
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FHWA Resource Center 9
Roundabouts and Road Users
» From Pedestrians 17
» To Bikes
» To Cars
» To Trucks
» To Farming equipment
» To Oversized trucks
» To Transit
Photo Source: Isebrands
Roundabout Categories & Typical Footprint
» Mini‐roundabouts
» 45 to 90 ft diameter
» Mountable center island
» Single‐Lane Roundabouts
» 90 to 180 ft diameter
» Low to high approach speeds
» Multilane Roundabout
» 150 to 300 ft diameter
» Hybrid designs common
Source of Images: Google Earth
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FHWA Resource Center 10
Variables that Affect Footprint
» Number of Lanes» Traffic Volumes
» Turning movements
» Diameter» Large Vehicles (Bus, Truck)
» Approach Geometry
» Sidewalks, Crosswalks, Multi‐use Paths
» Bike Lanes
Photo Source: CH2MHill
Planning Level Capacity ‐ AADT
Source: NCHRP 672, Exhibit 3‐12
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FHWA DRAFT Calibrated Capacity Model ‐ SLR
Source: FHWA
Roundabout Examples
Source of Images: Google Earth
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Mini Roundabout ‐ Shakopee (Scott County) MN
23Photo Credits: Tony Winiecki, Scott County MN
Mini Roundabout – Harford County, MD
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Main St. and Center St. Hamburg, NY
Image Source: NYSDOT
Single Lane ‐ Urban Compact
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135 ft
95 ft
140 ft
75 ft
85 ft
Mt Horeb, WI
130 ft
63 ft45 ft
Single Lane Roundabout
Source: San Diego, CA and Kings Beach, CA
http://tahoetopia.com/webcam/kings‐beach‐construction_cam_cafe
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Hybrid (2x1) Roundabout
Source: Waunakee, WI Eagle, CO
Single Lane Roundabouts
Source: Hopeland, CA Source: Hwy 88 Minden, NV
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Multi Lane Roundabouts
Photo Source: Isebrands Source: Google Earth
Source: Isebrands Source: City of Richfield, MN
Large Vehicles
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Transit‐Video
Source: City of Richfield, MN
Photo credits: Isebrands
Bikes at Modern Roundabouts
Photo credits: Isebrands
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Accessibility at Modern Roundabouts
Raised Crosswalk Pedestrian Hybrid Beacon
Rectangular Rapid Flash Beacon
Photo credits: Isebrands, FHWA
Education – Videos and Websites
http://www.youtube.com/watch?v=OvoFjirrgYA
http://safety.fhwa.dot.gov/intersection/
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Corridor Applications
US 6
Source: Google Earth Avon, CO
» Why are they important?» Roundabouts are still fairly “new”» Roundabout design not in academic curriculum
» Not every agency has a roundabout expert on board (and that is okay)
» An unbiased opinion almost always adds value
» You can learn a lot from a peer review – it makes you a better designer
» On‐call contract or pre‐qualified designer until in‐house expertise are developed (Iowa DOT, Kansas DOT, GDOT)
Peer Reviews
Source of Images: Google Earth
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Summary
» Safe» Most vehicles average 15 to 25 mph thru intersection
» Fewer conflict points
» Reduce probability of right angle, injury type crashes
» Reduces fatal and injury crashes on average by 80%
» Efficient» All movements (LT, TH, RT) have equal priority
» 24 hours a day (little stopping during off peak)
» Smart» Game changing design in terms of safety and operations
» Provides flexibility where none may have existed before
Thank You • Questions and Discussion
Hillary N. Isebrands, PE, PhD
FHWA Resource Center, Safety & Design Technical Service Team• Lakewood, [email protected] • (720) 963‐3222 office • (720) 545‐4367 cell
Source of Images: Isebrands, Google Earth, Isebrands
Clearwater, FL MnDOT
FSU