The chunk of Interstate 5 spanning the river collapsed around 7 p.m. local time, which authorities said began after a semituck bearing an oversized load struck a steel beam, the Seattle Times reported.
The impact caused the bridge to wobble, then fall into the water. A gold pickup with a trailer and an orange SUV went with it.
"You talk miracles,” said Dan Sligh, 47, who was in the pickup with his wife, said in an interview outside the hospital. “I don’t know what you want to call it. When you’re sitting down in the water and all that mangled metal of the bridge. You look around and you pinch yourself.”
“Forward momentum just carried us right over and as we saw the water approaching,” he said. “You just hold on as tight as you can. Then just a white flash and cold water.
Sligh said his shoulder was dislocated and his wife knocked unconscious, but he was able to pull himself and her out of the truck and keep them both above water until help arrived.
The other driver, a 20-year-old man, was also able to get out of his vehicle.
Rescuers said they don't think anybody else went into the water, but would search Friday morning to be sure.
Although the 58-year-old bridge was inspected last year and repairs made, Washington Transportation Secretary Lynn Peterson said, it had been classified by the National Bridge Inventory as "fracture critical," meaning damage to just one major structural part could take the whole thing down.
Authorities said the bridge will take at least three weeks to be fixed and reopen, forcing its daily traffic of about 70,000 vehicles to find an alternate route.
But despite the traffic nightmare descending on northwest Washington, everyone is mostly grateful the damage and death wasn't bigger.
"It's a miracle," said State Patrol trooper Jason Betts, the first officer on the scene after the collapse. "That's the only way I can explain it."