Description:

• raised islands, placed in intersections, around which traffic circulates
• motorists yield to motorists already in the intersection
• require drivers to slow to a speed that allows them to comfortably maneuver around them
• sometimes called intersection islands
• different from roundabouts

Applications:

• intersections of local or collector streets
• one lane each direction entering intersection
• not typically used at intersections with high volume of large trucks and buses turning left

Design/Installation Issues: typically circular in shape, though not always usually landscaped in their center islands, though not always often controlled by YIELD signs on all approaches, but many different signage approaches have been used key design features are the offset distance (distance between projection of street curb and center island), lane width for circling the circle, the circle diameter, and height of mountable outer ring for large vehicles such as school buses and trash trucks

Potential Impacts:

• no effect on access
• reduction in midblock speed of about 10 percent; area of influence tends to be a couple hundred feet upstream and downstream of intersection
• only minimal diversion of traffic
• intersection collisions have been reduced on average by 70 percent and overall collisions by 28 percent
• can result in bicycle/auto conflicts at intersections because of narrowed travel lane
  

Emergency Response Issues:

• emergency vehicles typically slow to approximately 13 mph; approximate delay of between 5 and 8 seconds per circle for fire trucks
• fire trucks can maneuver around traffic circles at slow speeds provided vehicles are not parked near the circle

Other/Special Considerations:

• large vehicles may need to turn left in front of the circle (which could be unsafe at higher volumes); legislation may be required to legally permit this movement
• quality of landscaping and its maintenance are key issues
• landscaping needs to be designed to allow adequate sight distance
• care must be taken to avoid routing vehicles through unmarked crosswalks on side-street approach

Typical Cost:

• approximately $3,500 to $15,000 (1997 dollars)

1627 I ("Eye") Street, NW, Suite 600
Washington, DC
20005-3538 USA
Phone: 202-785-0060
Fax: 202-785-0609
Send comments to:
website@ite.org

SPEED HUMP | SPEED TABLE | RAISED INTERSECTION | CLOSURE | NEIGHBORHOOD TRAFFIC CIRCLE | CHICANE | CHOKER | CENTER ISLAND NARROWING