A section of Old Highway 99 north of Cook Road will be closed for about 18 months starting May 1 for construction of a new railroad overpass.
The existing 80-year-old wooden trestle overpass will be demolished and replaced by a concrete and steel structure.
The highway will be closed for about .3 miles from just north of Cook Road to Dahlstedt Road for the duration of the project.
Skagit County officials established a detour route along Interstate 5 several months ago.
“We’re telling people to add an extra 10 minutes to their trip,” county spokeswoman Bronlea Mishler said.
The county and its contractor have been waiting on approval from BNSF Railway in order to start work.
The project is receiving about $16.5 million in grant funding, including $12 million from a state highway bridge replacement program, Mishler said. The remaining $1.5 million for the project will come from county funds, she said.