Neighborhood Traffic Operations: Traffic Circle Program
Traffic circles are effective at reducing traffic speeds at intersections, as well as the number and severity of collisions. Especially when installed in a series, traffic circles also provide an overall traffic calming effect along the entire s treet corridor. Over the last 30 years, the City of Seattle has installed over 1,000 traffic circles on city streets.
Due to high demand and limited funding, we have developed a process for prioritizing traffic circles.
Step 1 - Community Request
All requests made prior to July 15th will be considered for the following year’s construction season.
Step 2 - Preliminary Traffic Safety Analysis
It is important to note that not all intersections are suitable for traffic circles. For example, traffic circles and most other traffic calming devices cannot be installed on streets that are Seattle Fire Department primary emergency response routes, because of their effect on emergency response times.
Residents who submit their traffic circle request by July 15th will receive a letter from SDOT, sometime in September. If the intersection does not qualify for SDOT funding, information on Other Funding Sources will be provided.
Step 3 - Petition Process
If preliminary analysis suggests your intersection is a strong candidate for funding, you will be asked to confirm community support. You will receive a petition form in the mail, as well as a map of affected property owners. The requestor, or other neighborhood volunteers, must collect signatures from affected households (owners or renters) and businesses (property owner or business owner) in the petition areas, typically within one block of the intersection. Only one signature per household or business owner is needed. A minimum of 60% of households and businesses must be in favor of the traffic circle.
Signed petitions must be returned by the deadline (we generally provide for a 6 week circulation period) to be considered for the following year’s construction. A completed petition does not guarantee a traffic circle will be constructed. Rather, the completed petition ensures that there is public support for the project, and allows SDOT to complete the final ranking of traffic circle requests. In addition, property owners at the intersection must be notified.
Step 4 – Speed and Volume Analysis
Building on the preliminary safety analysis, SDOT will conduct speed and volume studies. This information, along with the collision history, will be used to complete the final ranking of the intersections using established Traffic Circle Scoring Criteria. The highest scoring traffic circles will be constructed. The exact number of circles that will be built is dependent on available funding.
Step 5 - Design & Construction Overview
The traffic circle is made up of a 2’ wide concrete ring and reflectors are installed on the ring. The concrete ring is less than four inches high next to the road so fire trucks or other large vehicles can drive over a portion of the traffic circle without harming the landscaping. There are also reflective object marker signs in the center of the traffic circle so that the traffic circle is more visible at night. For more information on traffic circle design, see Traffic Circle Typical Design.
SDOT encourages landscaping in all traffic circles that are of sufficient size to support landscaping. Maintenance of the landscaping is the responsibility of the community, and several volunteers must be identified before the traffic circle is designed and constructed. If there are not enough identified volunteers, SDOT will eliminate the landscaping component from the traffic circle, and pave the interior of the circle instead.
It generally costs $15,000 to completely construct a traffic circle. SDOT staff designs the circle, and construction is normally completed by SDOT crews. Costs are kept down by not installing irrigation. Water must be brought from nearby residences to help establish the landscaping in the traffic circle.
Once a traffic circle is constructed, SDOT Urban Forestry provides a list of approved plants for the neighborhood to choose from. Plants are placed on this list because of their low mature height and ability to withstand the harsh environment of a traffic circle. Plants will be delivered to the home of a neighborhood volunteer either in the spring or fall. The neighborhood volunteer is encouraged to coordinate a planting party for all the volunteers on the block. Residents are encouraged to plant additional material from the approved plant list as space allows, as long as the mature height is not above 24" and stays within the borders of the circle. Future, ongoing maintenance is the responsibility of the community. Replacement plants are typically not available through SDOT, but access to free mulch and an invitation to the annual plant exchange is provided if you are registered with Urban Forestry.
If larger scale restoration is needed, community members can apply for a $250 sparks grant through Department of Neighborhoods at http://www.seattle.gov/neighborhoods/nmf/smallsparks.htm
If you have any further question regarding Traffic Circle Landscaping, please call SDOT Urban Forestry at 684-TREE (8733).
A meeting may be held in the neighborhood to discuss the project. Maintenance of the traffic circle landscaping and identification of landscape volunteers in addition to the traffic analysis and design concept will be discussed.