The Washington Transportation Department says an average of 71,000 vehicles a day used the stretch of Interstate 5 through Mount Vernon that is now blocked by the collapse of the Skagit River bridge.
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 nearby and mostly used for local traffic between Mount Vernon and Burlington.
The department also is recommending detours using Highway 20 and Highway 9 that add tens of miles to a trip.
Officials are urging drivers to avoid the area if possible.
The Interstate 5 bridge that collapsed into the Skagit River was built in 1955 and was inspected two times last year in August and November.
Transportation Department spokesman Noel Brady in Seattle says it had a sufficiency rating of 47 out of 100. The state average is 80, according to an Associated Press analysis.
Brady says the bridge was 1,112 feet long and 180 feet wide with two lanes in each direction. There were four spans or sections over the water supported by piers. The span on the north side is the one that collapsed. The bridge was about 25 feet over the river.
It was a steel truss bridge, meaning it had a boxy steel frame. The vertical clearance from the roadway to the overhead supports was 14.6 feet.