Modern Roundabouts: Safety & Mobility Wrapped in a Pretty Package


Published on - 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.

Published in: Travel
1 Like
  • Be the first to comment

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide
  • 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

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