Traffic circle installation overview

In recent years, data showed that additional traffic calming tools were needed in some neighborhoods. Because of a decade-old City policy against installing new speed humps, the City’s Traffic Safety Committee (TSC) researched other physical traffic calming measures and found traffic circles to be the most effective option with installations beginning in 2016.  

What is a traffic circle and are they effective?

 Traffic circles are typically between 15 and 25 feet in diameter, placed at intersections of low-speed residential streets to reduce vehicle speeds and neighborhood cut through traffic. They are often placed in the middle of existing intersections with minimal changes needed. 

By forcing traffic to move to the right of the typical lane path, traffic circles effectively lower approach speeds and reduce the number and severity of collisions. The City of Seattle, for example, installed more than 1,000 traffic circles and documented 70 percent fewer collisions.

Can emergency vehicles, recreational vehicles and school buses utilize traffic circles?

Traffic circles can be designed to meet fire code and provide access to vehicle types necessary within residential neighborhoods. In Marysville, traffic circles have been tested using large city vehicles including a fire truck. In addition, traffic circles are installed utilizing mountable center island curbing with 3' minimum width driveable concrete aprons to enable access for even the largest vehicles.

Traffic Circle Standard Plan

How does the City decide where to install traffic circles?

The Traffic Safety Committee found the need for traffic calming on several neighborhood streets based upon documented conditions. These streets are typically wide, straight/flat neighborhood streets conducive to cut-through traffic and/or speeding. All roadways evaluated for traffic circles have a posted speed limit of 25 mph. The streets selected all have a larger percentage of drivers traveling well above the posted speed limit. The goal of traffic circle installation is to reduce vehicle speeds through neighborhoods and discourage drivers from using these streets to cut through neighborhoods.

Where are traffic circles now in place? Are they effective?

The City has installed seven (7) neighborhood traffic calming circle projects:

  • 71st Ave NE (64th ST NE (SR 528) to Grove ST)
  • 56th Ave NE (south of 132nd ST NE)
  • 92nd ST NE ( State Ave to 51st Ave NE)
  • 79th Ave NE ( 55th PL NE to 60th ST NE)
  • Beach Ave & Short ST
  • 3rd ST (State Ave to 47th Ave NE)
  • 2nd St (State Ave to 47th Ave NE)

The traffic circles have been successful in reducing traffic speeds, especially Excessive Speeds defined as drivers traveling greater than 10 mph over the speed limit. 

Traffic circle installation results

Location
Average Daily
Traffic (ADT)
Average
Speed (mph)
85% Speed
(mph)
% of vehicles
traveling greater than
10 mph over 25 mph
speed limit
All Locations Average
(Pre-Installation)
2087 29.9 34.5 14.2%
All Locations Average
(Post Installation)
1669 25.7 29.6 2.5%
Decrease 418 4.2 4.6 11.7
% Decrease
20.0% 14.0% 13.3% 82.4%