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.
A minimum of 30 feet of curbside parking must be prohibited on the through street at each corner of the intersection. Tri Met buses can maneuver around traffic circles at slow speeds provided vehicles are not illegally parked near the circles. 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.