Mini-circles can be used on residential streets to slow vehicle speeds.
Mini-circles are raised circular islands constructed in the center of residential or minor street intersections (generally not intended for use where one or both streets are arterial streets). They reduce vehicle speeds by forcing motorists to maneuver around them. Mini-circles have been found to reduce motor vehicle crashes by an average of 90 percent in Seattle, WA (Seattle has over 700 mini-circles). Drivers making left turns are directed to go on the far side of the circle prior to making the turn. Signs should be installed directing motorists to proceed around the right side of the circle before passing through or making a left turn. Mini-circles are commonly landscaped (bushes, flowers, or grass), most often at locations where the neighborhood has agreed to maintain the plants. In locations where landscaping is not feasible, traffic circles can be enhanced through specific pavement materials.
Mini-circles are an intersection improvement as well as a traffic-calming device and can take the place of stop or yield signs. Many unwarranted four-way stop signs are installed because of the demand for action by the community.
Mini-circles must be properly designed to slow vehicles and benefit pedestrians and bicyclists. Right-turning vehicles are not controlled at an intersection with a mini-circle, potentially putting pedestrians and bicyclists at risk if not designed correctly.
Therefore, tight curb radii should complement this treatment to discourage high-speed right-turn maneuvers. The occasional larger vehicle going through an intersection with a traffic circle (e.g., a fire truck or moving van) can be accommodated by creating a mountable curb in the outer portion of the circle.
Purpose
* Manage traffic at intersections where volumes do not warrant a stop sign or a signal
* Reduce crash problems at the intersection of two local streets
* Reduce vehicle speeds at the intersection
Considerations
* Do not make generous allowances for motor vehicles by increasing the turning radii—this compromises pedestrian and bicyclist safety.
* Larger vehicles that need access to streets (e.g., school buses and fire engines) may need to make left-hand turns in front of the circle.
* Other traffic control is often not needed; however, if needed, use yield, not stop signs.
* Mini-circle landscaping should not impede the sight distance.
* Treat a series of intersections along a local street as part of a neighborhood traffic improvement program.
Estimated cost
The cost is approximately $6,000 for a landscaped traffic mini-circle on an asphalt street and about $8,000 to $12,000 for a landscaped mini-circle on a concrete street.
