Wash. Rev. Code § 47.48.040
Except as provided under RCW 47.48.060, when any state highway, county road, or city street or portion thereof shall have been closed, or when the maximum speed limit thereon shall have been reduced, for all vehicles or any class of vehicles, as by law provided, any person, firm, or corporation disregarding such closing or reduced speed limit shall be guilty of a misdemeanor, and shall in addition to any penalty for violation of the provisions of this section, be liable in any civil action instituted in the name of the state of Washington or the county or city or town having jurisdiction for any damages occasioned to such state highway, county road, or city street, as the case may be, as the result of disregarding such closing or reduced speed limit.
RCW 47.48.040