The four-lane Interstate 5 bridge -- more than half a century old -- collapsed about halfway between Seattle and Vancouver, British Columbia, Washington State Trooper Mark Francis said.
Francis said he did not know what caused the collapse, which came at the start of one of the busiest holiday weekends of the year in the US, Memorial Day weekend. The collapse came before sundown on a clear day. The state Transportation Department said it was investigating whether an oversize truck load may have struck the bridge.
"I hit the brakes and we went off," Sligh told reporters from a hospital, adding he "saw the water approaching ... You hold on as tight as you can."
Sligh, his wife and another man in a different vehicle were dumped into the chilly waters of the Skagit River when the span collapsed last evening. They were injured, but authorities said it appeared nobody was killed in the bridge failure that raised the question about the safety of aging spans.
Sligh and his wife were taken to Skagit Valley Hospital with non-life-threatening injuries. The other man was reported in stable condition at United General Hospital in Sedro-Woolley, hospital CEO Greg Reed said.
Authorities are trying to determine what caused the bridge to collapse about 100 kilometres north of Seattle in Skagit County.