Wash. Rev. Code § 81.53.090
When a highway crosses a railroad by an over-crossing or under-crossing, the framework and abutments of the over-crossing or under-crossing, as the case may be, shall be maintained and kept in repair by the railroad company, and the roadway thereover or thereunder and approaches thereto shall be maintained and kept in repair by the county or municipality in which the same are situated, or if the highway is a state road or parkway, the roadway over or under the railroad shall be maintained and kept in repair as provided by law for the maintenance and repair of state roads and parkways.
The railings of over-crossings shall be considered a part of the roadway. Whenever a highway intersects a railroad at common grade, the roadway approaches within one foot of the outside of either rail shall be maintained and kept in repair by highway authority, and the planking or other materials between the rails and for one foot on the outside thereof shall be installed and maintained by the railroad company. At crossings involving more than one track, maintenance by the railroad company shall include that portion of the crossing between and for one foot on the outside of each outside rail. The minimum length of such planking or other materials shall be twenty feet on installation or repairs made after February 24, 1937.
RCW 81.53.090