Traffic circles are raised islands placed in an intersection. They are landscaped with ground cover and street trees. Traffic circles require drivers to slow to a speed that allows them to comfortably maneuver around them.
The primary benefit of traffic circles is they reduce the number of angle and turning collisions. An additional benefit is they slow high-speed traffic.
Traffic circles are very effective at lowering speeds in their immediate vicinity. Traffic circles are most effective when constructed in a series on a local service street.
Effectively reduce vehicle speeds
Improve safety conditions (for example, there are fewer left-hand turn crashes involving other vehicles)
Require some parking removal
Can cause bicycle/auto conflicts at intersections because of narrowed travel lane
Can restrict emergency or transit vehicle movement if vehicles are parked illegally near the circle
Traffic circles cost approximately $5,000 to $15,000 each.
A minimum of 30 feet of curbside parking must be prohibited on the through street at each corner of the intersection.
Transit Service Impacts:
Tri Met buses can maneuver around traffic circles at slow speeds provided vehicles are not illegally parked near the circles.
Emergency Services Impacts:
Fire trucks can maneuver around traffic circles at slow speeds provided vehicles are not illegally parked near the circles.
Noise impacts are minimal. There may be some noise related to vehicles decelerating and accelerating near the circles.
If well-maintained, traffic circles can be very attractive. However, there are also a lot of traffic control signs and pavement markings associated with circles that are not so attractive.
Traffic circles are less effective at T-intersections and difficult to design for offset intersections.
Examples In Portland:
SE Lincoln/Harrison, between 20th and 60th Ave. SE Clinton, between 12th and 52nd Ave. NE 15th, north of Broadway.