Wash. Rev. Code § 81.64.010
The legislative authority of the city or town having control of any public street or road, or where such street or road is not within the limits of any incorporated city or town, then the board of county commissioners wherein such road or street is situated, may grant authority for the construction, maintenance and operation of electric railroads or railways, motor railroads or railways and railroads and railways of which the motive power is any power other than steam, together with such poles, wires and other appurtenances upon, over, along and across any such public street or road and in granting such authority the legislative authority of such city or town or the board of county commissioners, as the case may be, may prescribe the terms and conditions on which such railroads or railways and their appurtenances shall be constructed, maintained and operated upon, over, along and across such road or street, and the grade or elevation at which the same shall be maintained and operated.
RCW 81.64.010