About 71,000 vehicles a day used the stretch of I-5 through Mount Vernon before it was blocked by the bridge collapse.
Mount Vernon is about 60 miles north of Seattle and 40 miles south of the Canada Border. The roadblock on both directions of I-5 is expected to cause a major disruption in trade and tourism between Seattle and Vancouver, British Columbia.
The Transportation Department has set up detours. The closest is within sight of the I-5 bridge and mostly used for local traffic between Mount Vernon and Burlington.
Traffic is being diverted off southbound I-5 at Exit 230. For an alternate route, take eastbound Highway 20, then south on S. Burlington Blvd. and west on E. College Way (SR 538) to southbound I-5.
Northbound I-5 traffic must exit at Exit 227. An alternate route is east to E. College Way to northbound Riverside Drive-S. Burlington Boulevard, then west on George Hopper Road to I-5.
To use SR 9 as an alternate northbound route, bypassing Mount Vernon, take Exit 221 at SR 534 east to northbound SR 9 to SR 20 westbound to I-5.
Officials are urging drivers to avoid the area if possible.