Design
In 2018, the City began collecting concurrency mitigation fees to fund necessary improvements to enable the intersection to support the traffic demand, or concurrency. An alternative analysis and intersection type evaluation was completed to identify the appropriate intersection improvement. A signalized intersection and roundabout design alternatives were analyzed as the potential intersection improvement options meeting the Washington State Department of Transportation (WSDOT) requirements. This analysis, known as the Intersection Control Evaluation (ICE), concluded a roundabout is the best solution for this location.
The ICE study involved the forecasting of the future demand for the base model and the testing of various project alternatives to determine the optimal control solution for an intersection. Factors such as traffic safety, transportation standards, and geographical characteristics were considered when determining the final design decision.
The following schematic drawing shows a preliminary design concept for a roundabout at SR 503 and NW Onsdorff Boulevard intersection:
(Select a map below to expand the view)