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While traveling down the highway it is likely that you have, at some point, been behind a semi truck. Whether attempting to cut gas mileage by drifting close behind or gaining on them to make the pass, many drivers have come dangerously close to a trucks back end.

If you are one of those drivers, you’ve probably noticed the red and white striped bar that hang down from the trailer looking somewhat like a guardrail between you and the big rig’s tires. This steel barrier is known as a Mansfield bar and is designed to keep following vehicles from going under the trailer in the event of a crash.

The Mansfield bar was created after the death of actress Jayne Mansfield, whose tragic end came when the car she and her children were riding in slammed into the rear of a semi truck. The collision sheared the roof of the vehicle almost completely off killing Mansfield and her two adult passengers. Her three children who were in the back seat survived the accident.

The invention of the Mansfield bar was hailed as a success after initial crash tests showed that it worked to prevent cars from going underneath a semi’s trailer. However, it was later discovered that while the Mansfield bar did indeed work, its success hinged largely on the angle of impact. When vehicles collided with the semis rear coming straight at the bar, it was successful. However, a change to the trajectory led to a decreased success rate. In fact, when anything less than 30 percent of the vehicles front end hit the bar, the success rate dropped dramatically.

Semi trucks are everywhere on the road. While they may sport various safety measures such as the Mansfield bar, the danger they pose to other drivers largely rests with their operators. Driver fatigue and distracted driving are some of the leading causes of semi truck accidents. Safety additions are important, but nothing can replace responsibility. Having a Mansfield bar on the back of a semi doesn’t mean the driver can forget safety.  An injured individual can still hold the driver or their carrier legally accountable.