Firefighters swarmed the FedEx delivery truck to cut its driver from underneath a large steel beam that crushed the hood but missed the cab. A second beam landed on the back of the truck.
The cause of the collapse was being investigated.
The driver, Robert Sylvester, 45, of Chico, Calif., was pulled free about two and a half hours after he was trapped. He suffered only a sprained ankle and minor cuts, his wife, Carol, told The Associated Press.
"We've gone from thinking he was absolutely the unluckiest person to the luckiest," she said, taking her husband home from Enloe Medical Center in Chico.
The Early Show co-anchor Harry Smith spoke with Sylvester and the men who pulled him from the wreckage, Fire Capt. Sean Norman and Capt. Chad Porter a paramedic.
Sylvester said the collapse happened so fast that he didn't immediately have a chance to think about dying. "It happened too quickly to really have that thought go through my head, but I didn't think of a good outcome," he said.
Norman said that he saw a large cloud of dust, which indicated that a significant incident had occurred. Porter said that it was like solving a puzzle to rescue Sylvester and avoid further danger. "It was initially easy to make access, but it was difficult to extricate him," Porter said.
As he was being rescued, Sylvester said that he stayed as calm as he could. He put his trust in the rescue workers who helped him keep his cool.
The construction worker, Jeffrey Doll of Olivehurst, who was on top of the structure, also was injured when it collapsed about 7:15 a.m.
"He rode it 50 feet down to the ground. It's incredible that he's going to survive that one," said Mark Dinger, a spokesman for the California Department of Transportation.
Doll, 39, was in serious condition with a fractured pelvis, fractured left elbow and broken lower left leg at the hospital in Chico, hospital spokeswoman Sharon Cuglietta said.
The overpass was being built over Highway 149 where it intersects with Highway 70, about an hour north of Sacramento, Calif., Highway Patrol spokeswoman Karen Ogle said. The project began last summer and was scheduled to be completed in the fall of 2009.
Highway 149 had been closed overnight and until 5 a.m. Tuesday while workers from private contractor FCI Constructors Inc. erected concrete columns and steel tubes weighing 2,400 to 3,000 pounds that were held together with cables and steel I-beams, Dinger said.
FCI has no record of health and safety violations, and a random inspection in July 2005 found no infractions, said Kate McGuire, a spokeswoman with the state Division of Occupational Safety and Health.
FCI Constructors President Curtis Weltz, who arrived at the site after the collapse, said he did not yet know what caused the structure to collapse.
"There's a bunch of different possible scenarios. It's never happened to us before," Weltz said.
Jacque Underdown, a spokeswoman for the project's second contractor, Granite Construction Co. of Watsonville, Calif., said the company was cooperating with investigators.
Carol Sylvester said her husband, a father of three who has worked for FedEx since 2003, had begun his delivery route and was driving north when he saw something fall.
"He saw something fall, he thought a box. Then things started hitting the truck," she said. "I think he's in shock and glad. It was a long time in the truck and he's glad to be home."
Construction crews planned to stabilize the remaining structure and remove an estimated 70 tons of steel worth about $50,000 that crashed onto the highway.
"The top priority right now is to stabilize this and get it reopened to traffic," Dinger said.
Meanwhile, FedEx was evaluating the "large number of packages" damaged in the accident.
"When it is deemed safe and all official investigations are complete, the packages will be retrieved and returned to our local facility," said spokesman Robert Boulware.
The Department of Transportation was rerouting traffic until the road could be reopened, possibly as early as Wednesday morning.
Associated Press reporters Samantha Young in Sacramento and Marcus Wohlsen in San Francisco contributed to this report.