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What’s the point of the metal guards on the back of trucks?

How many times have you wondered what that funny metal bar is used for on the back of trucks? Will it cause additional destruction if a car rear ends it? Considering how dangerous truck accidents are in the first place, are these bars a good idea?

Well believe it or not, these metal bars (commonly referred to as underride guards) are actually safety measures to prevent truck rear end accidents from becoming fatal.

The Purpose of Underride Guards 

The U.S. Department of Transportation estimates that nearly 4,000 deaths occur each year as a result of collisions between passenger cars and large trucks. One common cause of fatalities to occupants of cars is the car sliding underneath the truck in a rear or side collision. Due to the horrific nature and high risk of these types of accidents, trucks are now required to have heavy duty metal bars—underride safety guards—attached to the back of the trailer in order to help prevent vehicles from being able to slide underneath.

They have two main protective functions: to act as a barrier and to absorb impact force.

  • Barrier: anyone who has seen a truck knows that its trailer is always higher than a normal car. The truck's tires are large and therefore raise the truck's axis. Unfortunately, it's this height that causes problems in the event of an accident. Since the trailer is raised to approximately the same height as a car's windshield, it allows space for a car to wedge itself underneath it. However, by having the guards placed on the same axis level as normal vehicles, cars are unable to pass the barrier to slide underneath
  • Impact absorber: during any collision, the main areas of a car that absorb impact are the bumpers, the engine block, and the vehicle's axis. However, during underride collisions, these impact absorbers don't have a chance to impact anything, let alone absorb the force, until they are under the trailer. This means that instead of being absorbed, the entirety of the accident's force is exerted into the impact of the trailer into the upper compartment of the car. This force can ultimately cause the windshield to shatter, the entire top of the car to sheer off, and everything in the cab to become crushed. However, when an underride guard is present, the bumper and engine block will absorb the force rather than causing so much damage

So, the next time you pass a truck you may want to take a second to appreciate the importance of that simple metal bar.