The Winston stock car race was winding down and fans were streaming across a pedestrian bridge to the parking lot when two loud cracks could be heard above the murmur of the crowd.

With the second crack, an 80-foot section of the 320-foot concrete-and-steel walkway snapped in half and fell onto the highway outside Lowe's Motor Speedway on Saturday night.

A total of 107 people received medical treatment, said track spokesman Jerry Gappens. Fifty-three remained hospitalized today, three in critical condition.

"It was an amazing sight; everyone disappeared," said Mike Aquino, 41, of Atlanta, who was treated for minor injuries. "There was a mass of people, and then they were all gone.

"For a split second, I was thinking I was going to die, and then I realized I was going to live."

Piercing screams filled the humid night air as adults and children slid and tumbled to the highway 17 feet below in a jumble of broken concrete, coolers, sneakers and grills.

"I heard it crack the first time, and the second time it went down," said Greg Southern. "It was just awful."

"All of a sudden, the bottom fell out from everybody," said Roger Dunham, who had just started across the bridge.

Steel bands in the concrete-and-steel bridge failed, said Don Idol, an assistant engineer with the state Department of Transportation. Exposed in the rubble, the steel showed signs of corrosion, probably caused by moisture, he said.

"It could be a material problem, or it could be a construction problem, maybe structural fatigue," said Don Goins, the state Department of Transportation's chief engineer for field operations. "We just have to look at that, and we don't know the answer yet."

The $1 million walkway was built in 1995 for pedestrian traffic only. It was inspected when it first opened, but inspections weren't required since then because it is owned by the speedway. State-owned bridges must be inspected every two years.

The walkway, and another one 500 yards away, carried thousands of fans over four-lane U.S. 29 to parking lots across the way. There were no vehicles on the road below.

Track officials estimate that 180,000 people attended Saturday night's NASCAR all-star race.

Tragedy has struck the speedway before, including last May, when three spectators were killed by a tire that was sent spinning into the stands after a crash. A lawsuit filed by the victims' families was settled this month for an undisclosed amount.

The next race scheduled at the speedway is next Sunday's Coca-Cola 600. Qualifying races start Wednesday.