1 Roundabouts – Be Brave and Be Careful! Presenter: Steve Thieken, PE, PTOE Burgess & Niple, Inc. APWA 2008 Public Works Congress & Exposition New Orleans, Louisiana August 19, 2008 Presenter Background B.S. Civil Engineering – University of Dayton M.S. Transportation Engineering – The Ohio State University 15-years experience in Transportation and Traffic engineering and planning Roundabout Convert! ITE Roundabout Taskforce Member
Transcript
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Roundabouts – Be Brave and Be Careful!Presenter:
Steve Thieken, PE, PTOEBurgess & Niple, Inc.
APWA 2008 Public Works Congress & ExpositionNew Orleans, Louisiana
August 19, 2008
Presenter Background
B.S. Civil Engineering – University of Dayton
M.S. Transportation Engineering – The Ohio State University
15-years experience in Transportation and Traffic engineering and planningRoundabout Convert!ITE Roundabout Taskforce Member
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AcknowledgementsCity of Dublin– Ken Richardson, PE– Jeanie Willis, PE– Paul Hammersmith, PE– Barb Cox, PE
City of Hilliard– Letty Schamp, PE– Butch Seidle, PE
Delaware County, Ohio– Chris Bauserman, PE– Ryan Mraz
City of Athens, Ohio– Andy Stone, PE
Kittelson & Associates
Objectives
• Provide some roundabout basics• Illustrate a wide range of real situations where
roundabouts provide an excellent intersection solution (Be brave!)
• Explain some lessons learned (Be careful!)
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A roundabout...
… is an intersection with a generally circularshape.
… requires all entering traffic to yield to circulating traffic.
… has appropriate geometric features to ensure slow entering and circulating speeds.
The Modern Roundabout
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The Modern Roundabout
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Roundabouts are a subset of circular intersections…
Roundabouts
Rotaries
Neighborhoodtraffic circles
Others
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Other Circular Roadway Designs
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dtsThe Neighborhood Traffic Circle
Other Circular Intersection Designs
The Rotary
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Other Traffic Circles: Fort Worth, TX
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Conversion of Rotary to Roundabout:Kingston, NY
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Key Roundabout Features
Key Dimensions
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Why Roundabouts (vs. signals)?
Much saferMore efficient (less delay)More aesthetic design opportunitiesReduced noiseReduced vehicle emissions – greener!Lower operating costs (and less energy consumption)Access managementLess R/W required for approach lanes
Roundabouts are Safer
-76%-35%
-87%-72%-71%-32%-81%-29%
-60%TOO FEW
-67% TOO FEW
SIMILAR SIMILAR
Source: NCHRP 572
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Fewer Conflict Points
Reduces number of conflict points from 32 to 8
Reduced Severity of ConflictsSeverity related to relative velocities of conflicting streams
Rear-end
Sideswipe
Angle
Angle
Head-on
Least severe
Most severe
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Roundabouts are Usually More Efficient
Roundabout gives higher capacity and lower delays than All-Way Stop Control under same conditions
Roundabout likely to have higher delays than Two-Way Stop Control if TWSC is operating without problems
Roundabout within capacity will generally produce lower delays than signal under same conditions
Maximum ADT (4-leg intersection)
0
10,000
20,000
30,000
40,000
50,000
60,000
0% 10% 20% 30% 40%Left Turn Percentage
Max
imum
AA
DT
(K=0
.10)
1 Lane (50% Minor)
1 Lane (33% Minor)
2 Lanes (50% Minor)
2 Lanes (33% Minor)
Source: Roundabouts: An Informational Guide
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Pedestrians at Roundabouts
“Personally, I love them, . . . you only have to stop one lane of traffic, then go to the middle and wait. The cars can’t go much faster than 20 mph through the roundabout so the crossing aspect is great”
From the Howard-Suamico—Denise Haltom, School Crossing Guard, Suamico, Wisconsin
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Pedestrian Crash StatisticsBritish studyShows that all three main classifications of roundabouts produce lower pedestrian crash rates
Dutch StudyShows reductions in crash rates after intersections where changes from signalized to roundabouts89% reduction in pedestrian injury crashes
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Four potential vehicular conflicts exist for each crossing:1. Crossing movements on red
(typically high-speed, illegal)2. Right turns on green (legal)3. Left turns on green (legal for
permitted left turn phasing)4. Right turns on red (typically
legal)
Signalized Intersections Safe?
Pedestrian Crashes at Roundabouts
Two potential vehicular conflicts exist for each crossing1. Conflict with
entering vehicles2. Conflict with
exiting vehicles
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Lower speed is safer for pedestrians
15%
32 km/hr20 mph
50 km/hr30 mph
65 km/hr40 mph
45%
85%Chance of pedestrian death increases with vehicle speed
Source: United Kingdom
Space Requirements
Source: NCHRP 572
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Why Roundabouts (vs. signals)?
Much saferMore efficient (less delay)More aesthetic design opportunitiesReduced noiseReduced vehicle emissionsLower operating costs (and less energy consumption)Access managementLess R/W required for approach lanes
Design Considerations
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Bicycles in the Roundabout
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Cyclist Movements at Roundabouts –Circulating as a Vehicle
Bikes merge with motor vehicles
Bikes re-enter bike lane
Lower motor vehicle speeds (15-20 mph)
Fewer conflict points with motor vehicles
Source: NCHRP 572
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Cyclist Movements at Roundabouts –Circulating as a Pedestrian
Bikes join shared path with pedestrians
Bikes return to bike lane
Bicyclists cross as pedestrians
Source: NCHRP 572
Pedestrians
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Access Board RulingRevised Draft Guidelines for Accessible Public Rights-of-WayR305.6.2 Signals. At roundabouts with multi-lane crossings, a pedestrian activated signal complying with R306 shall be provided for each segment of each crosswalk, including the splitter island.YOU MAY WANT TO PLAN FOR THIS!NCHRP 3-78
Exercise Care WhenBuildings or expensive property on cornersOther traffic control devices are close byBottlenecks are close byThere are steep grades and unfavorable topographyThere are heavy pedestrian and/or bicycle movementsLocated within a coordinated signal network
Speed Profiles Design to slow trafficSmooth transitions -relative “R” speed differences should be less than 12-mph, preferably less than 6-mph
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Path Overlap
On multi-lane roundaboutsGuide drivers into proper lane Path overlap can result in above average # of crashes
Large TrucksP
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Emergency Vehicles
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TrucksUse CAD tools to check truck paths
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LightingIlluminate pedestrians and bicyclistsIlluminate curbs and vehicle pathMake driver aware of approaching roundabout
Landscaping/Sight Distance
Don’t block critical sight distancesReducing sight distance will help to reduce traffic speedsUse landscaping to make roundabout apparent
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Maintaining Traffic during Construction
Maintaining Traffic During Construction
Keep it as simple as possibleUse closures and detours where possibleIdentify critical vehicular and pedestrian paths and seasonal considerationsMinimize constructing in “pieces”Wider footprint may provide an opportunity to maintain through traffic
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MOT (continued)
Be careful using “temporary” roundabouts– Safety– Use full pavement markings & signing
Lighting should be operationalPublic perception (first impression!)
QUESTIONS?
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Five Case Studies
U.S. 33 and S.R. 161/Post Road Interchange -Dublin, OhioSawmill Parkway Extension - Delaware County, Ohio Hilliard Triangle Project - Hilliard, Ohio Avery Road South Corridor Study - Dublin, OhioRichland Avenue Improvements – Athens, Ohio
U.S. 33 and S.R. 161/Post Road Interchange - Dublin, Ohio
Diamond Interchange Three-lane roundabouts at the exit ramp terminals Three-lane roundabout at an adjacent intersection2009 Construction
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ODOT & FHWA Approval
Operational Benefits
North Leg (Off-Ramp) A 3.0 A 3.6 B 14.0 B 16.3 D 53.2 D 43.0
West Leg (SR 161) A 3.6 A 3.0 A 9.4 A 6.4 D 53.9 D 48.0
South Leg (University) A 4.8 A 6.6 B 19.0 C 25.5 D 47.1 D 48.7
East Leg (SR 161) A 1.8 A 2.4 A 4.6 A 4.4 C 20.7 D 39.4
