RCW 36.75.200: Bridges on city or town streets.

The boards of the several counties may expend funds from the county road fund for the construction, improvement, repair, and maintenance of any bridge upon any city street within any city or town in such county where such city street and bridge are essential to the continuation of the county road system of the county. Such construction, improvement, repair, or maintenance shall be ordered by resolution and proceedings conducted in respect thereto in the same manner as provided for the laying out and establishing of county roads by counties, and for the preparation of maps, plans, and specifications, advertising and award of contracts therefor.