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WEI ZHANG F H W A O F F I C E O F S A F E T Y R & D
2 0 2 - 4 9 3 - 3 3 1 7
W E I . Z H A N G @ D O T . G O V
Field Testing, Marketing, and Crash Analyses of Mini-roundabouts
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FHWA Safety R&D Intersection Program
Field evaluation of innovative design concepts
Fundamental and Exploratory Research
Development and Support of Analysis Tool
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Field Evaluation Projects
Displaced Left Turn Intersections (2 sites in UT, LA)
Double Crossover Diamond Interchanges (8 sites in MO, NY, TN, KY)
Restricted Crossing U-Turn Intersections (9 sites in MD)
Intersection Speed Reduction By Lane Narrowing (10 sites in PA, OH, MO, MD)
Detection-Control System (8 sites in FL, IL, LA, TX)
Mini-roundabout (GA, MD, NY)*
*: Recruiting up to 10 sites for evaluation
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Products Developed
Roundabout Informational Guide
Signalized Intersections Informational Guide
Alternative Intersections Informational Guide
Field Evaluation Reports on DLF
RCUT
D-CS
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Fundamental and Exploratory Researches
Safety impacts of access mgmt policies and design techniques
In-vehicle pedestrian detection using stereo vision technology
Eye tracking study to detect driver visual distraction other abnormal events
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Software Tools Developed
Surrogate Safety Assessment Model (SAAM)
Interchange Safety Assessment Tool (ISAT)
Alternative Intersection Selection Tool (AIST)
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Mini-Roundabout, what is it?
A single-lane roundabout with inscribed diameter in the range of 50 to 80 ft
Defining feature is a traversable central island (and split islands) to handle large vehicles
Advantages include: Higher capacity than stop control
Fit into existing intersection ROW
Improve intersection operating efficiency and safety
Low cost ($25,000 to $50,000 per intersection)
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Design Objectives of the Mini Central Island
Traversable by large vehicles
Un-comfortable for small vehicles
Not causing problems for winter maintenance
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Suitable Locations for Mini-roundabout
Intersections on 2-lane or 3-lane high volume collector roads
Post speed 35 mph or less
Low truck volume
Comparable traffic volume from major and minor approaches
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Recommended Signing and Pavement Markings
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Partnership Responsibilities
FHWA Provides free technical supports (design templates, capacity
analysis, review of geometric and signing designs)
Conducts before/after operational & safety evaluations
Tailors evaluation to individual site’s improvement objectives whenever possible
Participating Agencies Identify suitable sites (intersections on 2 or 3 lane roads)
Cover costs of engineering design and construction
Provide available traffic counts and crash data
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Examples of Constructed Minis
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Mini-roundabout, France
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Mini-roundabout in England
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Mini-roundabout in Australia
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To Be Constructed, Atlanta, GA
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Newly constructed in Takoma Park, MD
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Best to use raised but traversable islands
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Surface Material of central Island Stamped epoxy or concrete
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Use edges that are raised
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Temporary Traffic Circle in Phoenix, AZ
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P A Y A T T E N T I O N T O T H E U S E F U L I D E A S T H A T C A N B E U S E D W H E N D E S I G N I N G M I N I -
R O U N D A B O U T S
The Following Examples are NOT mini-roundabouts
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Small size 1-lane roundabout, FL
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Small Roundabout in Phoenix, AZ
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Quasi Mini Grant Ln & Trailside Dr, Columbia, MO
Grant Ln is a high volume collector road with post speed of 35 mph
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Traversable Central Island Grant Ln & Trailside DR, Columbia, Mo
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Split Island, Grant Ln & Trailside DR, Columbia, Mo
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Takoma Park, MD
Large vehicle getting around mini-roundabout
Driving around a mini-roundabout
Traversing a mini-roundabout
Multiple cars entering a mini-roundabout
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Stevensville, MD
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Basic Characteristics
Traffic volume = 600 vph (595 vph collected): Leg 1: 160 vph, Leg 2: 240 vph, Leg 3: 200 vph.
Traffic movement: Left-turn (67%), Right-turn (33%)
Traffic composition: Car (46%), SUV/pickup (51%), and Truck (3%)
Average Travel time through the roundabout Right-turn: 2-3 sec Left-turn: 5-7 sec (car/SUV), 10 sec (truck)
Stopping Behavior Completely Stop (15%), Rollover and No-Stop (85%)
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Stevensville MD
Large vehicle exiting expressway
Camper
Long truck and boat
Long truck making right and left turns
Motorcycle and trucks etc
Simultaneous entries
Small truck and driver confusion
SUV with tow-car
Vehicle stream
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Contact Information Mini Roundabouts Evaluation
Wei Zhang (FHWA Safety R&D) (202) 493-3317, [email protected]
Joe Bared (FHWA Ops R&D) (202) 493-3314, [email protected]
Hillary Isebrands (FHWA Resource Center) (720) 963-3222, hillary.isebrands.dot.gov
Ramanujan Jagannathan (VHB) (703) 847.3071 x5240, [email protected]
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D - C S
Questions?
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Lake Stevens, WA (2016)