Wash. Rev. Code § 47.56.250
Whenever a proposed toll bridge, toll road, toll tunnel, or any other toll facility of any sort is to be constructed, any city, county, or other political subdivision located in relation to such facility so as to benefit directly or indirectly thereby, may, either jointly or separately, at the request of the transportation commission advance or contribute money, or bonds, rights-of-way, labor, materials, and other property toward the expense of building the toll facility, and for preliminary surveys and the preparation of plans and estimates of cost therefor and other preliminary expenses. Any such city, county, or other political subdivision may, either jointly or separately, at the request of the transportation commission advance or contribute money or bonds for the purpose of guaranteeing the payment of interest or principal on the bonds issued by the commission to finance the toll facility. Appropriations for such purposes may be made from any funds available, including county road funds received from or credited by the state, or funds obtained by excess tax levies made pursuant to law or the issuance of general obligation bonds for this purpose. General obligation bonds issued by a city, county, or political subdivision may with the consent of the commission be placed with the department of transportation to be sold by the department to provide funds for such purpose. Money, or bonds, or property so advanced or contributed may be immediately transferred or delivered to the department to be used for the purpose for which contribution was made. The commission may enter into an agreement with a city, county, or other political subdivision to repay any money, or bonds or the value of a right-of-way, labor, materials, or other property so advanced or contributed. The commission may make such repayment to a city, county, or other political subdivision and reimburse the state for any expenditures made by it in connection with the toll facility out of tolls and other revenues for the use of the toll facility.
RCW 47.56.250