Detailed description given by Montana Highway Patrol on the horrific incident:

Here is a backstory behind the video: MHP Trooper Wade Palmer and Cadet (now Trooper) Timothy Templeton arrived at the scene of a crash involving a mother and her two small children. Conditions were hazardous as the crash occurred during a blizzard. The dash-cam footage captures a series of subsequent collisions occurring after the initial crash that disabled the family’s vehicle. In the first subsequent collision, a semi-truck hits the passenger vehicle parked on the shoulder of the road, causing the mother to be ejected from the vehicle. She landed in the highway median. Trooper Palmer located the victim in the median and rendered aid. While that was happening, Cadet Templeton saw an out-of-control truck and trailer headed directly toward Trooper Palmer and the victim. Templeton shouted a warning and Trooper Palmer was able to pull himself and the victim to safety within seconds, thereby saving his life and that of the mother. Thankfully, everyone survived. The mother and her two children are on the road to recovery.