The three hurt Saturday at the outdoor Harrisburg MotorSports Complex were taken to a hospital in nearby Eugene, Linn County Sheriff Tim Mueller said. Sheriff's officials said their injuries were not life-threatening; their identities and conditions were not available early Sunday.
The 1975 Ford pickup, fitted with large tractor tires, had slowed to about 10 mph just before coming to a stop, Guilford said. Emergency crews responded to the complex about 30 minutes after "Monster Air 2012" began Saturday.
Dan Mills, who built and owns the complex and served as the announcer for Saturday's event, said numerous precautions had been taken to keep spectators safe. But he said the truck's hydraulic steering went out suddenly during a two-truck race and that the driver, after losing control of the vehicle, couldn't stop it as it veered into the spectator area.
"It went to the right and there wasn't anything he could do to stop it," Mills told The Associated Press on Sunday. "This was my worst fear - what happened ... It was the freakiest thing I've ever seen."
Mills said he has been in touch with the three victims. He said they included a father and son, and a man believed to be in his early 20s. Mills said the truck did not run over any of the spectators but that its front end merely "pushed them back."
"I think they just basically got hit by the front of the truck," he said.
Sheriff's officials identified the driver as Kyle Atchley.
Mills said he plans to continue the three-day show Sunday, with added precautions that include not allowing spectators into the area when the accident occurred. He said about 1,000 people attended the Saturday event.
Associated Press reporter Mark Evans contributed to this report from Phoenix.