Under-ride guards on tractor trailers meant to prevent severe injuries during rear-end collisions often fail to do their job, according to the Insurance Institute for Highway Safety.

The group is calling for drastic changes in 18-wheeler safety standards after crash tests revealed car drivers can be decapitated if the run into the back of the large trucks.

"Damage to the cars in some of these tests was so devastating that it's hard to watch the footage without wincing," Insurance Institute for Highway Safety president Adrian Lund said in a statement. "If these had been real-world crashes there would be no survivors."

Under-ride occurs when a vehicle rear-ends a tractor trailer, forcing the hood of the car to go under the truck.

Guards were put in place to prevent this, but the U.S. National Highway Traffic Safety Administration admits improvement still need to be made.

The Insurance Institute for Highway Safety said almost 80 percent of all car-truck crashes that involve cars rear-ending trucks result in significant amounts of under-ride.