Officials in the north-western American state of Washington say the collapse of a road bridge into a river was caused by a truck with an oversized load hitting a girder.
Vehicles and people were thrown into the water of the Skagit river but there were no fatalities or serious injuries.
The four-lane bridge near Mount Vernon is on the main route between the cities of Seattle and Vancouver, Canada.
National Transportation Safety Board chairperson Deborah Hersman says the lowest point of clearance on the bridge was 4.1 metres but the truck had been permitted a load height of 4.6 reports Reuters.
Ms Hersman says the bridge was elliptical in shape, shorter on the sides than in the middle.