Traffic Circles
Description:
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.
Purpose:
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.
Effectiveness:
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.
| Advantages | Disadvantages |
|
Effectively reduce vehicle speeds
Improve safety conditions (for example, there are fewer
left-hand turn crashes involving other vehicles)
Visually attractive |
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 |
Cost:
Traffic circles cost approximately $5,000 to $15,000 each.
Parking Impacts:
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:
Noise impacts are minimal. There may be some noise related to
vehicles decelerating and accelerating near the circles.
Other Considerations:
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.