Wash. Rev. Code § 47.04.180
On the recommendation of their public works departments or designees, counties or cities can petition the department of transportation to create a "twenty-four hour headlight policy" on state highways in their respective jurisdictions. The department shall develop criteria for approval or disapproval, such as traffic volume, accident statistics, and costs of signs. The department shall notify all counties about this program.
A jurisdiction requesting such a policy shall periodically report to the department regarding its educational efforts. A jurisdiction may petition the department to remove such a policy.
The jurisdiction shall educate its citizens on the "twenty-four hour headlight policy." The department shall place and maintain appropriate signs along the designated highway. Participating jurisdictions shall share in the cost of signing in an amount as determined by the department.
RCW 47.04.180