Wash. Rev. Code § 47.08.020
For the construction, alteration, repair and improvement of state highways, county roads, or city and town streets in the state of Washington which are part of the public highway system, the good faith of the state of Washington is hereby pledged to make available funds sufficient to equal the sums appropriated to the state by or under the United States government during succeeding fiscal years and to use and expend the same within one year after the fiscal year for which appropriated, and in the manner and under the rules and regulations imposed by the secretary of commerce and to maintain, or cause to be maintained, the highways or roads constructed or improved with the aid of funds so appropriated, and to make adequate provisions for carrying out such maintenance.
RCW 47.08.020