Wash. Rev. Code § 47.12.010
Whenever it is necessary to secure any lands or interests in land for a right-of-way for any state highway, or for the drainage thereof or construction of a protection therefor or so as to afford unobstructed vision therefor toward any railroad crossing or another public highway crossing or any point of danger to public travel or to provide a visual or sound buffer between highways and adjacent properties or for the purpose of acquiring sand pits, gravel pits, borrow pits, stone quarries, or any other land for the extraction of materials for construction or maintenance or both, or for any site for the erection upon and use as a maintenance camp, of any state highway, or any site for other necessary structures or for structures for the health and accommodation of persons traveling or stopping upon the state highways of this state, or any site for the construction and maintenance of structures and facilities adjacent to, under, upon, within, or above the right-of-way of any state highway for exclusive or nonexclusive use by an urban public transportation system, or for any other highway purpose, together with right-of-way to reach such property and gain access thereto, the department of transportation is authorized to acquire such lands or interests in land in behalf of the state by gift, purchase, or condemnation. In case of condemnation to secure such lands or interests in land, the action shall be brought in the name of the state of Washington in the manner provided for the acquiring of property for the public uses of the state, and in such action the selection of the lands or interests in land by the secretary of transportation shall, in the absence of bad faith, arbitrary, capricious, or fraudulent action, be conclusive upon the court and judge before which the action is brought that said lands or interests in land are necessary for public use for the purposes sought. The cost and expense of such lands or interests in land may be paid as a part of the cost of the state highway for which such right-of-way, drainage, unobstructed vision, sand pits, gravel pits, borrow pits, stone quarries, maintenance camp sites, and structure sites or other lands are acquired.
RCW 47.12.010
Urban public transportation system defined: RCW 47.04.082.
Right-of-way donations: Chapter 47.14 RCW.