Neighborhood traffic circles are:
- Horizontal speed control measures.
- Raised islands usually placed in the center of intersections.
- Typically circular in shape and can be landscaped, painted, or left
unfinished as long as they are easily noticed.
- Designed so that all traffic must yield to traffic within the circle.
A YIELD sign usually controls traffic on all approaches.
- Effective by impeding the straight-through movement of an intersection
and therefore causes drivers to slow their vehicles as they proceed
counterclockwise around.
- Ideal for residential applications.
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Typical Design:
- The design can vary significantly depending on the design purpose.
- The circles can be designed to be partially or fully mountable by
larger vehicles. This means that larger vehicles can ride over the whole
circle or part of the circle while making a tight turn or negotiating
the intersection.
- The Institute of Transportation Engineers has design recommendations.(2)
- The Pennsylvania Department of Transportation has design recommendations.(3)
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Placement Issues:
- Neighborhood traffic circles are typically used at unsignalized intersections
with average daily traffic volumes less than 3,500 vehicles.
- Neighborhood traffic circles are most effective at reducing vehicle
speeds when several are used in series.
- Areas with multiple neighborhood traffic circles typically find that
speeds are reduced 4-6mph.
- Neighborhood traffic circles may make it difficult for large trucks
(including emergency vehicles) to turn left. The circles can be designed
to be partially or fully mountable by larger vehicles (moving trucks,
fire engines...).
- Pedestrian crossings should be moved away from neighborhood traffic
circles.
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Approximate Cost:
- Installation costs of simple traffic circles that requires no modification
to the existing curbs, gutters, and drains ususally are between $3,000
and $8,000.
- If the installation is more complex and requires modification to the
right-of-way and other road features, the cost could exceed $20,000.(3)
- Landscaping the neighborhood traffic circle adds to the ongoing maintenance
costs.
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Comments:
- Proper signage and possibly lighting are necessary to ensure that
drivers understand how to properly negotiate the neighborhood traffic
circle.
- The center island doesn't necessarily need to be a circle; it an be
designed to fit the intersection configuration.
- Neighborhood traffic circles work well when installed in conjunction
with other measures such as: chokers and medians.
- When designing a neighborhood traffic circle, considerable attention
should be given to aesthetics.
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Advantages
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Disadvantages
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- Effective in reducing vehicle speed.
- Can significantly reduce serious motor vehicle collisions by
reducing right-angle conflicts.
- "The Insurance Corporation of British Columbia, summarizing
43 international studies, reported that circles reduce collisions
by 82 percent."(3)
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- May make left turn maneuvers difficult for emergency vehicles
and larger trucks.
- It is suggested that on-street parking be prohibited 30 feet
from the intersection.
- The potential exists for an increase in vehicle/bicycle accidents
and vehicle/pedestrian accidents as vehicles may not yield properly
or be deflected by the circle into a bicycle's or pedestrian's
path.
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