Each traffic circle is individually designed to fit the intersection without having to modify the street width or corner radii. Most of Seattle's local streets are 25 feet wide or less and traffic circles are usually 12 to 16 feet in diameter. A single unit truck having a 45 foot turning radius is used as a design vehicle to ensure that fire trucks can pass by the circle without running over the curbs. All intersections where circles are to be constructed are reviewed by the Fire Department and field tests are conducted where they have a specific concern. While traffic circles are designed to allow fire trucks to pass by them, they are constructed with a two foot wide mountable curb that allows fire trucks or larger vehicles, such as moving vans, to run over the curb without damaging the vehicle or the circle.
Landscaping is included in all the traffic circles currently being constructed.
The pavement inside the traffic circle is removed during construction to allow for drainage and accommodate tree roots. The landscaping plays two important roles, making the circle more attractive to the neighborhood residents and changing the character of the street making it less appealing for high speed driving. The local residents are required to maintain the plantings, which consist of ground cover and one to three trees. Residents are allowed to add their own low growing plants that will not block pedestrian or driver visibility. While landscaping makes traffic circles an attractive addition to a street, accident reduction is their greatest benefit.