Modern Roundabouts

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Modern Roundabouts

• James H. Ito, P.E.

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Introduction

• Modern Roundabouts became an effective Traffic
  Control strategy in 1966 when the British adopted
  the Yield upon Entry rule.
• I am currently the Traffic and Lighting Traffic
  and Lighting Design Engineer for the City of
  Milwaukee and the President of Active Traffic
  Alternatives.

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Topics of Discussion

• I will identify the distinguishing features of
  Modern Roundabouts
• You will learn why Modern Roundabouts are being
  built
• You will see images of Wisconsins Modern
  Roundabouts, those in use and some of those
  proposed

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What is a Modern Roundabout?

• Modern Roundabouts are part of the Family of
  Circular Intersections

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What is a Modern Roundabout?

• Modern Roundabouts are part of the Family of
  Circular Intersections
• Distinguishing Features
• Yield at Entry
• Speed Control by Deflection

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Why Build Modern Roundabouts?They Enhance Safety
Reduce Delay

• Conflict Points Reduced

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Why Build Modern Roundabouts?They Enhance Safety
Reduce Delay

• Conflict Points Reduced
• Crash Reduction Statistics

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Before and After Results for 24 Intersections in
US Converted from Stop Sign or Traffic Signal
Control to Modern Roundabouts

• 89 Reduction in Fatal and Incapacitating Injury
  Crashes
• 76 Reduction in All Injury Crashes
• 39 Reduction for All Crashes

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Why Build Modern Roundabouts?They Enhance Safety
Reduce Delay

• Conflict Points Reduced
• Crash Reduction Statistics
• Traffic Delays Minimized

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What Do They Look Like?

• Howard Roundabouts

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What Do They Look Like?

• Howard Roundabouts
• Proposed Roundabout in Milwaukee

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What Do They Look Like?

• Howard Roundabouts
• Proposed Roundabout in Milwaukee
• Proposed Roundabout in Mount Horeb

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What Do They Look Like?

• Howard Roundabouts
• Proposed Roundabout in Milwaukee
• Proposed Roundabout in Mount Horeb
• Proposed Roundabout in Brookfield

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Traffic Control Panacea?

• Modern Roundabouts should not be used in a
  Traffic Signal System
• Modern Roundabouts can be installed next to
  Signalized intersections
• Modern Roundabouts complement Traffic Calming
  Devices
• Modern Roundabouts enhance Street Landscaping and
  are often used to create Area Gateways

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What This Means

• Modern Roundabouts offer Communities and
  Neighborhoods an Attractive, Safe, and Efficient
  form of Traffic Control
• Modern Roundabouts can be more Efficient and
  Safer than traffic signals
• Modern Roundabouts should not be used in a
  Traffic Signal System

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What Has Happened

• Wisconsin Department of Transportation, Bureau of
  Transportation Safety funded Training, 1998
  through 2001
• Howard Modern Roundabouts have been constructed
• Roundabouts have been designed for several
  Wisconsin locations
• Wisconsin DOT has an Engineer on staff with
  Modern Roundabout Design Experience from Colorado

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Who To Contact?

• Ray Smith, Brown County Highway Department,
  920-492-4925
• Mark Johnson, Wisconsin DOT, District 1,
  608-246-3842
• James Ito, City of Milwaukee, DPW, 414-286-3263
• Your BOTS Regional Program Manager

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Geometric Design Recommendations

• Iterative Process
• Hand Sketching Preliminary Designs
• Fastest Vehicle Paths
• Truck Swept Paths
• Radial Alignment of Entries
• Vehicle Path Overlap
• Extended Splitter Island Treatment
• Successive Curves on HS Approach

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Capacity Software

• ARCADY British method with 50 confidence
  limits. Capacities predicted have been measured.
  Has crash prediction module.
• RODEL Same as ARCADY but with user specified
  confidence limits.
• SIDRA Australian method based on gap acceptance
  processes.

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Simulation Models

• Simulation model results are best used for
  relative comparisons.
• Do not conclude that the values found from the
  model are the same as field data.
• Perform sensitivity analysis by changing selected
  parameters over a range and comparing results.

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QUESTIONS?

• COMMENTS?