A man and his teenage son jumped from an Interstate 65 overpass Friday to avoid being struck by an oncoming semitrailer, police said.

Both fell 60 to 70 feet to the pavement below, said Sgt. Rich Kelly of the Indiana State Police.

Matthew M. Johnston, 14, fractured his spine and ankle and was airlifted to Methodist Hospital in Indianapolis, where he was being evaluated, said hospital spokeswoman JoAnn Klooz.

His father, Mark T. Johnston, 45, broke his arm and was in surgery Friday afternoon at Methodist, Klooz said.

The Johnstons, from Stanchfield, Minn., had stopped their car on the overpass at about 1 a.m. to assist a motorist who lost control of his car while driving south near Lafayette, police said. The car had struck the bridge retaining walls and had come to a stop in the right lane.

A semi driven by Everitt H. Coombs, 45, of Sturtevant, Wis., could not stop in time to avoid a collision with the wrecked car, police said. The semi crashed into the car, causing it to spin and forcing the Johnstons to jump to avoid the truck.

The driver of the wrecked car, Nathan G. Kloeppel, 16, of Lafayette, and the truck driver were not injured.