Wash. Rev. Code § 47.44.040
Whenever any bridge exists on the route of any state highway and crosses any stream, body of water, gulch, navigable water, swamp, or other topographical formation constituting the boundary of this state or the boundary of a county, city, or town of this state and the bridge is owned or operated by this state jointly with any such county, city, or town, or with any municipal corporation of this state, or with such other state or with any county, city, or town of such other state, the department is empowered to join with the proper officials of the county, city, or town, or the municipal corporation of this state or of such other state or of such county, city, or town of such other state in granting franchises to persons or private or municipal corporations for the construction and maintenance on the bridge of water pipes, flumes, gas pipes, telephone, telegraph, and electric light and power lines and conduits, trams and railways, and 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, or any other such facilities. All such franchises shall be granted in the same manner as provided for the granting of like franchises on state highways. Any revenue accruing to the state of Washington from the franchises shall be paid to the state treasurer and deposited to the credit of the fund from which this state's share of the cost of joint operation of the bridge is paid.
RCW 47.44.040
Urban public transportation system defined: RCW 47.04.082.