Wash. Rev. Code § 47.12.160
Whenever a part of a parcel of land is to be acquired for state highway purposes and the remainder lying outside of the right-of-way is to be left in such shape or condition as to be of little value to its owner or to give rise to claims or litigation concerning severance or other damage, and its value does not exceed the probable amount of the severance claims or damages, the department may acquire by gift, purchase, or condemnation the whole parcel and may sell that portion lying outside of the highway right-of-way or may exchange the same for other property needed for highway purposes. The provisions of this section do not apply if the taking of that portion of the land lying outside of the highway right-of-way would deprive any adjacent owner of an existing right of ingress and egress to his or her property.
RCW 47.12.160