Wash. Rev. Code § 81.112.090
Except in accordance with an agreement made as provided in this section, upon the date an authority begins high capacity transportation service, no person or private corporation may operate a high capacity transportation service within the authority boundary with the exception of services owned or operated by any corporation or organization solely for the purposes of the corporation or organization and for the use of which no fee or fare is charged.
The authority and any person or corporation legally operating a high capacity transportation service wholly within or partly within and partly without the authority boundary on the date an authority begins high capacity transportation service may enter into an agreement under which such person or corporation may continue to operate such service or any part thereof for such time and upon such terms and conditions as provided in such agreement. Such agreement shall provide for a periodic review of the terms and conditions contained therein. Where any such high capacity transportation service will be required to cease to operate within the authority boundary, the authority may agree with the owner of such service to purchase the assets used in providing such service, or if no agreement can be reached, an authority shall condemn such assets in the manner and by the same procedure as is or may be provided by law for the condemnation of other properties for cities of the first class, except insofar as such laws may be inconsistent with this chapter.
Wherever a privately owned public carrier operates wholly or partly within an authority boundary, the Washington utilities and transportation commission shall continue to exercise jurisdiction over such operation as provided by law.
RCW 81.112.090