Wash. Rev. Code § 47.52.100
In connection with the development of any limited access facility the state, county or incorporated city or town highway authorities are authorized to plan, designate, establish, use, regulate, alter, improve, construct, maintain and vacate local service roads and streets, or to designate as local service roads and streets any existing road or street, and to exercise jurisdiction over service roads in the same manner as is authorized for limited access facilities under the terms of this chapter. If, in their opinion such local service roads and streets are necessary or desirable, such local service roads or streets shall be separated from the limited access facility by such means or devices designated as necessary or desirable by the proper authority.
RCW 47.52.100