According to the Insurance Institute for Highway Safety, many fatal truck accidents are a result of a passenger car sliding under the rear of an 18 wheeler in a crash. In these collisions, known as ‘underride’ accidents, the windshield of the automobile impacts the deck of the semi trailer often crushing the upper part of the passenger compartment. There can be a high risk of decapitation during these types of accidents.
Because of this danger the trailers on 18 wheelers have a device known as a rear impact guard. This is a device like a bumper that extends directly down from the rear of the trailer. This safety device is intended to prevent a car from sliding under the semi trailer. Unfortunately a recent test by the Insurance Institute for Highway Safety (IIHS) indicates that the guards may fail in an accident.
To test the efficacy of the rear impact guards, the IIHS crashed a late model passenger car into the back of semi trailer. The car was moving at 35 miles per hour while the trailer was standing still. The force of the collision easily plowed through the guard leaving the passenger compartment to be struck directly by the deck of the semi. They also tested a version of the guards that are 75 percent stronger than the current requirement call for. This stronger version effectively kept the car from going under the trailer.
While a car’s collision with the guard may still result in a serious accident, the impact of the crash will be directed into the grill area in the front of the car, allowing safety features like crumple zones and airbags to be more effective while keeping the passenger compartment intact.
Source: Insurance Institute for Highway Safety “Underride guards on big rigs often fail in crashes; Institute petitions government for new standard” March 1, 2011