It happened in the eastbound lanes near Interstate 540 at the Durham/Wake County line.
After the first crash, the Good Samaritan stopped his WCA Waste Corporation truck and was walking back along the highway. That's when June Howard hit him.
"I was coming down 40 and I was going to get on the ramp there to 540, and all of a sudden I see him running, and so then I jerked the wheel back to the left cause I thought I was going to hit him," Howard told ABC11.
Howard said he couldn't avoid the man.
"Soon as I could get a place to pull over here and park, I pulled over and parked and starting running back over there to see about him," said Howard.
WCA identified the Good Samaritan as Chris Crowell. Witnesses said he was conscious and talking as paramedics tended to him, but police described his injuries as serious - including severe internal bleeding after being hit in the torso by a mirror on Howard's car.
Duke University Hospital said he was in critical condition after surgery.
Another man was also injured in the initial crash. His injuries were described as non life-threatening.