Some of the most devastating car accidents happen when another vehicle slams into the back of semi trailer. It can happen without warning when there’s low visibility on the roads or sudden stop in traffic. Most rear-end accidents are easy enough to walk away from, but rear-ending a semi can send the car under the trailer and crush the occupants. That’s what is referred to as underride.

At one point, underride was a sure way to die on the road. Unless the vehicle hitting the truck was traveling at a very slow pace, there was no way to reduce the severity of the accident. The oncoming vehicle typically would travel straight into the trailer. The trailer would crush the roof down and eliminate any space in the cabin for the passengers to safely exist in. Airbags are completely useless. Seatbelts made no difference.

The difference between today and just two decades ago is a change in the design of the rear ends of trailers carried by semis. Now most trailers have guards under the trailers of large semis. Most drivers will recognize this metal bar typically covered in reflective tape riding under the trailer and gave it no further thought. This bar could be the difference between life and death because there’s no feature in passenger cars to protect against underride.

However, there are still many dangers to underride accidents. These types of car crashes haven’t been eliminated because the bars are only the most effective in direct collisions. Every major trailer under crash tests passed when a car was aimed directly at the trailer going about 35 miles per hour. When about 50 percent of the car hits the guard, there is a majority of trailers that pass the test. When only about 30 percent of the car makes contact with the trailers, most guards were ineffective.

Rear-end accidents are far too common and underride is far too deadly for the average driver not to take heed when they are traveling behind a semi-truck with a trailer. Watch your distance and speed whenever you are behind a truck. Remember that your chances are greatest for survival if you can reduce speed and hit the guard rail head on as opposed to a glancing blow.