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Participation in the Neighborhood Traffic Control Program
(How to Build a Traffic Circle in Your Neighborhood)
Participation in the Program | Community Support | Traffic Safety Analysis | Design and Construction | Point Criteria | Landscaping
If you have any questions about the Neighborhood Traffic Circle Program, or are interested in applying for a traffic circle, please contact 684-0353.
Please note: The City of Seattle has decided to postpone its participation in the America in Bloom contest until next year. With the limited time until judging and the need to mobilize multiple neighborhoods and community groups, Seattle could not put its best face forward in time. However, the city is very excited about participating in next year's contest and urges citizens who are interested in helping to let us know. You can do so by contacting Urban Forestry at 684-TREE (8733). We will be sure to contact you as we take steps later this year to become an America in Bloom champion.
Participation In The Program
 Because of high demand and limited funding, an evaluation process for determining projects to be included in the NTCP has been established. This process involves the following steps, which must be completed before an intersection may be considered eligible. (Locations with physical characteristics that do not allow the feasible placement of a traffic circle will not be considered.)
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Step 1 - Community Request
SDOT requires support from the residents of the affected area before constructing a traffic circle. Responsibility for completion of this step lies with the community and involves the following:
An individual or group must make a request for inclusion in the current NTCP evaluation period by calling SDOT at (206) 684-0353. All requests should be made prior to July 31; any request received after this date will be considered for funding in August of the following year.
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Step 2 - Preliminary Traffic Safety Analysis
SDOT will evaluate the safety record of each location based on crash history.
At this stage, if the location does not qualify for funding, the contact person listed on the request will be notified by mail. Information about other potential funding sources may be provided.
If a location ranks sufficiently high on our prioritization list for NTCP funding, the contact person will be notified by mail, with a petition with a map of affected properties..
Step 3 - Petition Process
If the neighborhood decides to proceed with the traffic circle project, petition forms will be given to the applicant, and signatures must be gathered from at least 60% of the households (owners or renters) and businesses (property or business owner) within one block of the proposed traffic circle. Only one signature per household is needed. Signed petitions must be submitted to SDOT by October 15, to be considered for the following year's construction. Completed petitions can be mailed or delivered to: Seattle Department of Transportation, Key Tower, 700 Fifth Avenue, Suite 3900, Seattle, WA 98104-5043.
Step 4 - Traffic Safety Analysis
After receiving a valid petition, SDOT will conduct speed and volume studies. The data will be used to prioritize the location for construction using the Point Criteria for Traffic Safety Analysis.
Community Meeting (optional)
A meeting may be held in the neighborhood to discuss the project, including results of the traffic analysis, the design concept, and the procedures leading up to construction. Maintenance of the traffic circle landscaping, an important component of this project, and identification of a landscape volunteer will also be discussed during the meeting. |
Step 5 - Design & Construction Overview
Traffic circles are designed according to the existing geometry of each intersection and sized to accommodate the passage of emergency vehicles.
The Fire Department, Metro/King County Transit and other agencies review locations for new circles and may conduct a field test to check for maneuverability. Then, final plans are made and sent to construction crews with specifications. The first visible evidence that a circle will be built is its outline drawn in the intersection. In general, asphalt circles are built on asphalt streets and concrete circles are built on concrete streets. The outer rim of the circle is reinforced so that larger vehicles can go over it if necessary. Once the outer rim is built, the street is broken out of the center if it is to be landscaped. Finally, soil is added and the necessary signs are installed.
After construction, the circle will be monitored for a period of six months to one year. During this time, traffic speeds and volumes are measured to help determine the effectiveness of the circle. If a volunteer signs up to maintain plantings, soil and plants will be supplied; otherwise, it will be covered in asphalt.
NOTE: The City of Seattle Standard Plans and Standard Specifications for Road, Bridge, and Municipal Construction are available online at www.seattle.gov/util/Engineering/
Standard_Plans_&_Specs/index.asp
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Measuring for and laying out the traffic circle design.
Construction phase
Standard Reflector Sign
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Example of Traffic Circle Specification
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Point Criteria
Accident History
Points are determined from annual Accident Rates - average number of reported accidents over the past three years. |
| Points |
Annual Accident Rate (accidents/year) at intersection |
| 0.5 |
If accidents on a midblock section of street exceed 2 per year over the last three years. |
| 1 |
0.5 - 0.875 |
| 2 |
0.876 - 1.250 |
| 3 |
1.251 - 1.625 |
| 4 |
1.626 - 2.000 |
| 5 |
2.001 - 2.375 |
| 6 |
2.376 - 2.750 |
Traffic Volumes
(Vehicles per Day - Average Weekday Traffic) |
| Points |
Traffic Volumes |
| 0.5 |
500 - 1100 |
| 1.0 |
1101 - 1700 |
| 1.5 |
1701 - 2300 |
| 2.0 |
2301 - 2700 |
Traffic Speeds
(85th Percentile Speed) |
| Points |
Traffic Speeds (mph) |
| 0.5 |
26 - 29 |
| 1.0 |
29.1 - 32 |
| 1.5 |
32.1 - 35 |
| 2.0 |
35.1 - 38 |
| 2.5 |
38.1 - 41 |
| 3.0 |
41.1 - 44 |
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Traffic Circle Landscaping
Overview
Neighbors are responsible for the planting and maintenance of the traffic circle after it has been built. Landscaping is installed during the planting season (spring or fall). An SDOT Urban Forestry employee takes input from residents about plant material selection during the months of January and June, depending on the season when construction is completed. Plants are chosen based on their drought tolerance, resistance to occasional car traffic and right-of-way landscaping guidelines, which promote visibility. The recommended plant list contains a variety of suitable plants that have performed well in the past. Plants are delivered to the home of the landscape coordinator in the spring or fall and a planting party usually follows. Residents are responsible for the maintenance of traffic circle plantings. Replacement plants are not typically available through the Traffic Calming Program if the originals die due to neglect or automobile run-overs. Funding for vegetation rehabilitation is available through the Department of Neighborhoods.
Plants Provided at the time of installation
More about the landscaping process:
Each year SDOT provides plants for between 60 to 120 new traffic circles, chicanes, triangles and medians. Purchases are made in bulk to keep costs down, so this requires selecting a common plant pallet that accommodates the needs of everyone. Although every effort is made to get the plants neighborhood groups request we sometimes need to make substitutions. As always, purchasing depends upon plant availability. So, we ask for flexibility and patience as we are serving a considerable number of neighborhood groups.
Groups may purchase their own plant material if they would like to plant sooner or have specialty plants in mind that we might not be able to get. SDOT can not reimburse groups for these expenses, but your planting plan should be sent to SDOT Urban Forestry for permitting before plant purchases are made. Flower bulbs are not provided, but they are a lovely addition and we encourage you to plant them! Daffodils, in particular, grow really well. They need little care and will increase in number as they bloom each spring!
A circle must be at least 14 feet in diameter to qualify for a tree. For a typical 16-foot diameter device we usually provide:
1 Tree
4-5 shrubs (no more than two different types)
12 perennials (no more than three different types)
2 Flats of groundcover (one type)
All shrubs and perennials are limited to two feet in height. Multi-stemmed trees and shrubs that can grow tall, such as roses and lilacs are not acceptable. It is also advisable not to plant shrubs that require shearing. Usually the plants remain long after the person willing to consistently maintain them has left.
Recommended Right-of-Way Plant List
Traffic Circle Maintenance Tips
Salmon Friendly Gardening Tips from Seattle Public Utilities
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