What is the purpose of the steel beam that hangs below the rear bumper of a tractor trailer?

Those steel bars to which you refer are safety devices called underride guards. They are designed to prevent passenger vehicles from sliding underneath trailers in rear-end collisions with semi-trucks. Crash tests by the Insurance Institute for Highway Safety found that most underride guards do a decent job of preventing passenger cars from sliding underneath when the front of a vehicle strikes the rear of a truck. However, crashes where the car hits the outer edge of a trailer could put passengers in greater danger since the part of the guard that sticks out toward the ends of the truck doesn’t have as much support as the center.

If you are involved in a rear-end collision with a semi-truck that stopped suddenly without warning, call the Memphis truck accident attorneys at Greer Injury Lawyers. We have the years of experience you need to file a successful claim.