A trucker was hauling a load of drilling equipment Thursday evening when his load bumped against the steel framework over the bridge. He looked in his rearview mirror and saw the span collapse into the water behind him.
Motorists should not expect to drive on I-5 between Mount Vernon and Burlington for many weeks and possibly months, Treece said.
Treece asked people to plan for an extra hour to make their way through detours around the collapsed bridge. There are three detour options northbound and two options southbound.
About 71,000 vehicles use that stretch of highway every day. Late Saturday morning, traffic was moving freely through the detours.
"We're expecting it to get worse as the day progresses," Treece said, noting that at 11 a.m., the cloudy skies and cool weather could be keeping Memorial Day weekend travelers at home.
State transportation officials began working on both a temporary solution and a permanent fix within hours of the bridge collapse, he said.
The goal is to get I-5 open as quickly as possible, while making sure the solution is as safe as possible, he added.
Officials were looking for a temporary, pre-fabricated bridge to replace the 160-foot section that failed, Gov. Jay Inslee said Friday. That option could be in place in weeks. Otherwise, it could be months before a replacement can be built, the governor said.
Inslee said it will cost $15 million to repair the bridge. The federal government has promised $1 million in emergency dollars and more money could come later, according to Washington's congressional delegation.
Contact Donna Blankinship at https://twitter.com/dgblankinship.