Wash. Rev. Code § 36.75.190
Upon report by the examining engineer for the erection and construction upon any county road, or for acquisition by purchase, gift or condemnation of any bridge, trestle, or any other structure crossing any stream, body of water, gulch, navigable water, swamp or other topographical formation, which constitutes a boundary, publication shall be made and joint hearing had upon such report in the same manner and upon the same procedure as in the case of resolution or petition for the laying out and establishing of county roads. If upon the hearing the governing authorities jointly order the erection and construction or acquisition of such bridge, trestle, or other structure, they may jointly acquire land necessary therefor by purchase, gift, or condemnation in the manner as provided for acquiring land for county roads, and shall advertise calls for bids, require contractor's deposit and bond, award contracts, and supervise construction as by law provided and in the same manner as required in the case of the construction of county roads.
Any such bridges, trestles or other structures may be operated free, or may be operated as toll bridges, trestles, or other structures under the provisions of the laws of this state relating thereto.
RCW 36.75.190