Jack knifing is usually the result of a breaking accident, and what happens is the trailer usually swings out at a 90-degree angle and it then comes to a rest. It can hit the driver as well as other drivers along the way.
There are many possible factors that can cause a semi-truck to jack knife. Things like road conditions, speed, weight of the load the truck might be carrying, and turning on a curved pass, can cause the truck to jack knife. It’s important to remember that semi-trucks also take a long time to break.