From the Washington State Department of Transportation:

Beginning at 10 p.m. on Friday, July 24, crews will fully close westbound SR 18 and reduce SR 18 eastbound to one lane at SR 167.

The closure is necessary to add a new bridge pier to support a new SR 167 southbound HOT lane as it travels over SR 18. The closure will stay in place around-the-clock and work should be completed with all lanes opening by 5 a.m. Monday, July 27.