The Car and Truck Fleet and Leasing Management Magazine

IIHS Petitions for Stronger Underride Guards on Tractor-Trailers

March 02, 2011

ARLINGTON, VA - The Insurance Institute for Highway Safety said it is petitioning the federal government to require stronger underride guards that will remain in place during a crash and to mandate guards for more large trucks and trailers.

IIHS said new institute crash tests and analysis demonstrate that underride guards on tractor-trailers can fail in relatively low-speed crashes -- with deadly consequences.

Rear guards are the main countermeasure for reducing underride deaths and injuries when a passenger vehicle crashes into the back of a tractor-trailer. In 2009, 70 percent of the 3,163 people who died in all large truck crashes were occupants of cars or other passenger vehicles. Underride makes death or serious injury more likely since the upper part of the passenger vehicle's occupant compartment typically crushes as the truck body intrudes into the vehicle safety cage.

"Cars' front-end structures are designed to manage a tremendous amount of crash energy in a way that minimizes injuries for their occupants," said Adrian Lund, IIHS president. "Hitting the back of a large truck is a game changer. You might be riding in a vehicle that earns top marks in frontal crash tests, but if the truck's underride guard fails -- or isn't there at all -- your chances of walking away from even a relatively low-speed crash aren't good."

The institute has studied the underride crash problem for more than 30 years, including mid-1970s crash tests demonstrating how then-current guards were ineffective in preventing underride, Lund said.

In the latest study, IIHS analyzed case files from the Large Truck Crash Causation Study, a federal database of roughly 1,000 real-world crashes in 2001-03, to identify crash patterns leading to rear underride of heavy trucks and semi-trailers with and without guards. Underride was a common outcome of the 115 crashes involving a passenger vehicle striking the back of a heavy truck or semi-trailer. Only 22 percent of the crashes didn't involve underride or had only negligible underride, a finding in line with prior studies, IIHS said. In 23 of the 28 cases in which someone in the passenger vehicle died, there was severe or catastrophic underride damage, meaning the entire front end or more of the vehicle slid beneath the truck.

The National Highway Traffic Safety Administration (NHTSA) has estimated that about 423 people in passenger vehicles die each year when their vehicles strike the backs of large trucks. More than 5,000 passenger vehicle occupants are injured.

The study raised questions about how and why guards failed and at what speeds, so IIHS conducted crash tests evaluating three semi-trailer rear guards complying with U.S. rules. Two of the trailers also are certified to Canadian requirements, which are more stringent than those of the United States in areas of strength and energy absorption.

"The aim was to see if some underride guards perform better than others and to identify what crash speeds and configurations produce different types of failure," Lund said. "Damage to the cars in some of these tests was so devastating that it's hard to watch the footage without wincing. If these had been real-world crashes there would be no survivors."

Decapitation is a serious threat in underrides. In three of the crash tests, the heads of the dummies in the car made contact with either the intruding trailer or the car's hood after it tore free and pushed into the occupant compartment.

"Under current certification standards, the trailer, underride guard, bolts and welding don't have to be tested as a whole system," Lund said. "That's a big part of the problem. Some manufacturers do test guards on the trailer. We think all guards should be evaluated this way. At the least, all rear guards should be as strong as the best one we tested."

Another problem, IIHS said, is that regulatory gaps allow many heavy trucks to forgo guards altogether. When they are present on exempt trucks, guards don't have to meet 1996 rules for strength or energy absorption.

"Underride standards haven't kept pace with improvements in passenger vehicle crashworthiness," Lund said. "Absent regulation, there's little incentive for manufacturers to improve underride countermeasures, so we hope NHTSA will move quickly on our petition."

For more details about the IIHS research, click here.   

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