Snow and ice caused a five car pile up, backed up traffic and sent two people to the hospital south of Ronan.
Montana Highway Patrol said one vehicle was trying to turn on Olsen Road.
North bound cars slowed and stopped.
But troopers said one vehicle appeared to be going too fast, and rear ended the line.
The investigator said a man who was injured, then got out of his vehicle and stood on the road.
The driver of a truck was heading north too, and came upon the scene of the wreck.
"Once he saw the guy on the road," said Montana Highway Patrol trooper Brian Casey,"he ditched his truck into the ditch. He tried to avoid hitting the driver that had jumped out of the vehicle and his actions probably saved some people lives."
The truck driver, Joe Fisher, said,"I witnessed a U Haul rear end a transit truck, spun him around the side of his truck into the guard rail. I was slowing down the driver of the transit truck," said Fisher," so to avoid hitting him I went off in the ditch."