Hollywood and traffic safety become forever entwined after the death of rising star Jayne Mansfield in 1967. According to Auto Week, Mansfield was riding in a car that crashed into the back end of a semi-truck. The accident killed all adults in the vehicle, but fortunately, the children all survived. Because of this accident, the government introduced the requirement for a safety device on trucks, which people often refer to as the Mansfield bar. 

This accident happened due to fog that prevented the driver from seeing the truck in front of it slowing down. Because commercial trucks sit higher than the typical car, it is very easy for the smaller vehicle to go underneath the larger one. This can take the top off the vehicle, resulting in very serious injuries.  The Mansfield bar, or underride guard, stops a smaller vehicle before it can continue under the vehicle, which can prevent deadly injuries. 

Ride underrun protection system 

The formal name for this bar is the ride underrun protection system. It is a steel bar that hangs down from the rear of the semi. The idea is that your car will hit that bar with its bumper, which will stop it from sliding under the truck. 

The issues 

The issue with the bar is that it works sometimes but not all the time. If your vehicle has a low bumper, the bar can simply push your hood back into your vehicle, allowing the bottom of your car to still go under the truck. In addition, this bar offers no protection along the sides of the truck, which also poses an underride risk.