Wash. Rev. Code § 47.56.070
The department of transportation may, in accordance with this chapter, provide for the construction and operation of toll tunnels, toll roads, and other facilities necessary for their construction and connection with public highways of the state. It may cause surveys to be made to determine the propriety of their construction and operation, and may acquire rights-of-way and other facilities necessary to carry out the provisions hereof; and may issue, sell, and redeem bonds, and deposit and expend them; secure and remit financial and other assistance in the construction thereof; carry insurance thereon; and handle any other matters pertaining thereto, all of which shall be conducted in the same manner and under the same procedure as provided for the constructing, operating, and maintaining of toll bridges by the department, insofar as reasonably consistent and applicable.
RCW 47.56.070