Wash. Rev. Code § 47.56.256
If the department deems it not inconsistent with the use and operation of any department facility, the department may grant franchises to persons, associations, private or municipal corporations, the United States government, or any agency thereof, to use any portion of the property of any toll bridge, toll road, toll tunnel, or the Washington state ferry system, including approaches thereto, for the construction and maintenance of water pipes, flumes, gas pipes, telephone, telegraph, and electric light and power lines and conduits, trams or railways, any structures or facilities that are part of an urban public transportation system owned or operated by a municipal corporation, agency, or department of the state of Washington other than the department of transportation, and any other such facilities in the manner of granting franchises on state highways.
RCW 47.56.256
Severability-1961 c 257: See note following RCW 47.56.253.
Urban public transportation system defined: RCW 47.04.082.