Washington Revised Code Title 36. Counties § 36.75.030. State and county cooperation

The state department of transportation and the governing officials of any county may enter into reciprocal public highway improvement and maintenance agreements, providing for cooperation either in the county assisting the department in the improvement or maintenance of state highways, or the department assisting the county in the improvement or maintenance of county roads, under any circumstance where a necessity appears therefor or where economy in public highway improvement and maintenance will be best served.