Traffic Circles/Intersection Islands

Device name(s): Traffic Circles/Intersection Islands

Traffic circle

Approximate Cost: $10,000 – $60,000 excluding landscaping

Speed Reduction: 4-6 mph

Definition: Traffic circles are raised circular islands constructed in the middle of an intersection. Traffic circles require motorists to maneuver around the circle to proceed through the intersection, which will result in motorist speed reduction.Traditional circles are “yield upon entry”, meaning that cars in the circle have the right of way and cars entering the circle must wait to do so until the path is clear. No automobile can travel in a straight path. Neighborhood traffic circles are raised islands placed within an intersection. They are not to be confused with modern roundabouts, which are applied it to a different set of circumstances. Neighborhood traffic circles have resulted in average reduction of speed by 11% (from 34.1 to 30.2 mi./h) and a 70% reduction in intersection collision – a 28% reduction in collisions overall.

Fast Facts:

  • Can be used on Local Street-  yes
  • Can be used on Collector- yes
  • Can be used on Arterial- no
  • Reduces Speed- yes
  • Reduces Volume- no
  • Noise Impact- no
  • Restricts Access- no
  • Bicyclist Impact- possible
  • Transit Impact- possible
  • Parking Impact- possible
  • Emergency Response Impact- no

Advantages:

  • reduces speed through an intersection
  • re-prioritizes traffic increase accessibility for local residents
  • provides area for landscaping
  • can reduce collisions in intersections
  • increases pedestrian and bicycle safety
  • can have positive aesthetic value
  • can come to street that wants

Disadvantages:

  • increases regular maintenance
  • wrong-way left-turns could occur
  • may make pedestrian/bicycle crossing confusing
  • may create shortcut
  • may be confusing to some drivers
  • some trucks cannot navigate left turns
  • landscaping requires watering and maintenance
  • may require the elimination of some on-street parking
  • expensive to install

Criteria/Application(s):

  • Most effective when built in a series
  • calming intersections, especially with neighborhoods where large vehicles are not a major concern, but speed, volume and secure problems
  • 85th percentile speed is 5 mph above the speed limit or greater
  • 60% of households in affected area must support

Traffic Circle or Intersection Island

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