Modern Roundabouts: Safety & Mobility Wrapped in a Pretty Package
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http://www.ohm-advisors.com - Mad about Modern Roundabouts: Coupling Safety and Mobility. This presentation delivers a primer on roundabouts, the differences between roundabouts, traffic circles and ...

http://www.ohm-advisors.com - Mad about Modern Roundabouts: Coupling Safety and Mobility. This presentation delivers a primer on roundabouts, the differences between roundabouts, traffic circles and rotaries, and the important rules of roundabouts.

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  • Modern Roundabouts 09/23/10
  • Modern Roundabouts 09/23/10 In their own way, rdbts may be intimidating to drivers. Single-lane rdbts are not really that hard to master, and drivers can acclimate to them rather quickly. However, the use of two or even 3-lane rdbts are not yet common and require a sophistication of design to get good results.
  • Modern Roundabouts 09/23/10
  • Modern Roundabouts 09/23/10
  • Modern Roundabouts 09/23/10
  • Modern Roundabouts 09/23/10 Here are the fundamentals for roundabouts. These apply for all rdbts, from a mini-rdbt in a subdivision handling maybe 100 vph in its peak, up thru a 3-lane rdbt, with by-pass lanes, serving upwards of 7,000 to 8,000 vph.
  • Modern Roundabouts 09/23/10
  • Modern Roundabouts 09/23/10 Again, you need to understand the score card for rdbts. Like other treatments there are good and bad points to consider. When done correctly … (summarize list) There have been a number of studies of US intersections converted from signals to Rdbts; they point to dramatic reductions in number & severity of crashes. Rdbts have far fewer conflict points. When used at interchanges, Rdbt = 6 merge + 6 diverge + 0 crossing = 12. Conventional ramps = 26 points, including 10 crossing.
  • Modern Roundabouts 09/23/10 For purposes of general guidance, note that I am suggesting that placing rdbts near RR grade crossings is a negative. However, there are an number of locations (many in the U.K, only a handful yet in the U.S) where a rail line passes directly thru the heart of a rdbt. It CAN be made to work; but the attempt should be left in the hands of experts.
  • Modern Roundabouts 09/23/10
  • Modern Roundabouts 09/23/10
  • Modern Roundabouts 09/23/10
  • Modern Roundabouts 09/23/10
  • Modern Roundabouts 09/23/10
  • Modern Roundabouts 09/23/10
  • Modern Roundabouts 09/23/10
  • Modern Roundabouts 09/23/10

Modern Roundabouts: Safety & Mobility Wrapped in a Pretty Package Presentation Transcript

  • 1. Jim Marcinkowski, PE ASCE, APWA & SWE Redding, California May 17, 2010
  • 2.  
  • 3.  
  • 4.
    • Short History of Driving in Circles
    • Some Roundabout Basics
    • Safety
    • Users (How To)
        • Pedestrians
        • Bicycles
        • Drivers
    • Mobility (Congestion)
    • Before/After Comparisons
    • Aesthetics
  • 5.
    • No Controls
    • Take Your Turn
    • Follow Rules of Road
  • 6.  
  • 7.
    • Right of Way Rule (Yield to Right)
      • STOP Signs
        • Police Control
          • Traffic Signals
            • Special Turn Lanes & Signals
            • Vehicle & Pedestrian Detection
            • Coordinated Signal Systems
  • 8.
    • Shape Controls
    • Movement
    View of Columbus circle, Circa 1915 (Courtesy: New York Department of Planning)
  • 9.
    • Circles, Small and Large
    • Really Big, High Speed Circles Are Called Rotaries
  • 10.
    • Yield-To-Right
    • Circulating traffic yield to the entering vehicles.
  • 11.  
  • 12.
    • Meanwhile in England…
  • 13.
    • Yield-To-Left
    • Entering vehicles yield to the circulating traffic.
  • 14.  
  • 15.  
  • 16.  
  • 17.  
  • 18.  
  • 19.  
  • 20.  
  • 21.  
  • 22.  
  • 23.  
  • 24.  
  • 25.  
  • 26.  
  • 27.
    • Roads Are The Most Dangerous
    • Public Facilities
    • On The Face Of The Earth
      • In the U.S., about 800 people are killed each week.
  • 28.  
  • 29. TRAFFIC SIGNALS ARE NOT SAFETY DEVICES
  • 30.
    • 32 Vehicle/Vehicle
    • 24 Vehicle/Pedestrian
  • 31.
    • 8 Vehicle / Vehicle
    • 8 Vehicle / Pedestrian
  • 32.  
  • 33. All crashes All injury crashes Serious injury & fatal crashes
  • 34.
    • Week by Week reporting of accidents (Feb, 2008)
    • - no accidents reported since 12/12/07 (source: West Bloomfield Township)
  • 35.
    • NO INJURY ACCIDENTS
    • Minor Damage
    • Majority of Citations
      • Failure to Yield
      • Unsafe Lane Change
  • 36. (17+ seconds curb to curb) (<4 seconds each crossing) Typical Intersection = 60’ vs. Roundabout = 13’ x 2
  • 37.  
  • 38.  
  • 39.  
  • 40.
    • Goals of Roundabouts:
      • Yield on entry
      • Slow, consistent speeds entering/ thru/ exiting
        • Size as small as practical
        • Path deflection on entry
      • Limits the number of vehicle to vehicle & vehicle to pedestrian conflicts
  • 41.
    • Narrated by
    • Paul W. Smith
  • 42.  
  • 43.
    • = Delay +
    • Fuel Wasted +
    • Pollution + …
  • 44.
    • Added Delay =
      • Fuel Consumption
      • Air Pollution
      • Noise
    • Excess Widening =
      • Resources to Pave
      • Storm Water Run Off
  • 45.
    • Expression of both:
        • Capacity
        • Driver perception
    • Ranges from ‘A’ (best) to ‘F’ (worst)
    • Primarily based on measure of average delay
  • 46.
    • Best demonstrated through a review of a case study:
      • US-23/THOMPSON ROAD
    • Tight Diamond Rural interchange
    • Thompson Road – 2 lanes
      • 2 lane bridge over US-23
    • US-23 – 4 lanes
      • On/off ramps – Single lane w/stop control
  • 47.  
  • 48.
    • Rural Interchange w/ Improvements
      • Widen Thompson Road to five lanes including bridge
      • Widen ramps for right and left turn lanes
      • Install traffic signals
      • Construction cost = $7 m
      • Need additional land
      • NOT SELECTED…
  • 49.
    • Roundabouts at Ramps
      • Do Not Widen Thompson Rd
      • Do Not Widen Ramps
      • Install Single-lane Roundabout at each ramp termini
      • Construction Cost = $ 2.5 M
      • No additional land needed
  • 50.  
  • 51.  
  • 52.  
  • 53.
    • Roundabouts At Ramps
      • Selected as the recommended alternative
        • Best LOS
        • Lowest delay
        • Lowest cost
  • 54.  
  • 55.  
  • 56.  
  • 57.
    • Half mile strip commercial area. 20,000 ADT
    • No access management = numerous turning conflicts
    • Existing pavement width = 80’ - “sea of pavement”
    • Two traffic signals w/third needed
    • New shopping center was being proposed.
  • 58.
    • Reduce speed through the section
    • Improve safety
    • Improve access for businesses and residential neighborhoods
    • Create pedestrian friendly environment
    • Improve aesthetics
  • 59.  
  • 60.
    • Reduce speed through the section
        • Reduction of 85 th percentile speed from 48 mph to 33 mph
        • Reduction in average delay time, i.e., it takes less time to drive this segment of road even with a 15 mph reduction in speed
  • 61.
    • Improve safety
        • Crash rate reduced 88% even with increased traffic flows from new development
        • Reduced severity of accidents
        • Reduce # of injuries.
        • Before rate = 10/year
        • After rate = 1/5 years
  • 62.
    • Improve access for businesses and residential neighborhoods
        • Over first five years after construction - 60% growth in sales tax revenue for this corridor. Nearly flat sales tax revenue growth for the rest of Golden, CO over same time period
        • Elimination of large traffic queues from parking lots
  • 63.
    • Create pedestrian friendly environment
  • 64.
    • Improve aesthetics
  • 65.  
  • 66.  
  • 67.  
  • 68.  
  • 69.  
  • 70.  
  • 71.  
  • 72.  
  • 73.  
  • 74.  
  • 75.  
  • 76.  
  • 77.  
  • 78.  
  • 79.  
  • 80.  
  • 81.  
  • 82.  
  • 83.
    • Defined roundabout
    • Use / location
    • Benefits
      • Safety
      • Traffic calming
      • Capacity
      • Environmental
        • Emissions - Stormwater
      • Aesthetics
  • 84.
    • Reduces the number & severity of crashes.
    • Reduces the number of conflict points.
    • Increases capacity, usually w/ fewer approach lanes.
    • Minimizes ROW needed.
    • Can be closely spaced (to structures, traffic signals or other Rdbts).
    • Adapts to unusual geometry.
  • 85.
    • May not be suitable for locations:
    • Imbalanced traffic flows,
    • Poor stopping sight distance,
    • Steep grades (>5%) w/ heavy truck traffic,
    • Close to railroad crossings,
    • Within system of coordinated traffic signals.
  • 86.
    • Existing congestion problems
    • Known safety problems
    • Balanced entering traffic volumes, or
    • High percentage turning movements
  • 87.
    • Roundabouts: An Information Guide, FHWA 2000
    • NCHRP 3-78 IMPROVING ACCESS TO ROUNDABOUTS AND CHANNELIZED TURN LANES FOR THE VISUALLY IMPAIRED
    • www.roundaboutsusa.com
    • www.ksu.edu/roundabouts/
    • www.alaskaroundabouts.com
    • www.roundabout.kittelson.com
    • West Bloomfield Township
    • RCOC
    • Dan Hartman – dhartman@ci.golden.co.us
    • Northeast Roundabouts
  • 88.
    • A Coupling of Safety and Mobility
    QUESTIONS?
  • 89.
    • Initial Costs To Build
      • Surface area paved
      • Staging construction
      • Traffic signs
      • Pavement markings
      • Traffic & pedestrian signals
      • Street lighting
    • Annual Costs To Operate
    • Electrical & Communication
    • Relamping
    • Depreciating equipment
    • Pavement markings
    • Crash damage to equipment
    • Emergency service providers responses to crashes
  • 90.
    • 8 Roundabouts in West Bloomfield Township / Farmington Hills – Joint MDOT, RCOC, City & Twp.
  • 91.  
  • 92.  
  • 93.  
  • 94.  
  • 95.  
  • 96.  
  • 97.  
  • 98.  
  • 99.  
  • 100.