California ? Authorities scrambled Monday to find at least nine drivers who apparently escaped from vehicles trapped in a weekend tunnel inferno that killed three people on a key transportation route.

Thirty-one vehicles were involved in the pileup in the curving tunnel on Interstate 5, but the California Highway Patrol has accounted for only 23 people, including two men and a 6-year-old boy who were killed.

If all of them were at the wheel at the time of the crash, excluding the boy, that leaves nine drivers unaccounted for. The number could be higher if there were passengers in those vehicles.

Investigators are confident only three people died, but CHP Assistant Chief Warren Stanley said they have no idea what happened to the others who left their vehicles to the flames.