Lagging Tractor-Trailer Standards Pose Decapitation Risk for Car Occupants

Rear-ending a tractor-trailer truck sounds pretty bad. But the reality is even worse, according to crash tests performed by the Insurance Institute for Highway Safety (IIHS), which is petitioning the government to strengthen rules for “underride” guards on the back of trucks.

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 per- cent 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, Institute 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 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.

Crash tests

The study raised questions about how and why guards failed and at what speeds, so the Institute conducted crash tests evaluating 3 semi-trailer rear guards complying with U.S. rules. Two of the trailers also are certified to Canadian requirements, which are more stringent than the United States when it comes to strength and energy absorption. The tests involved crashing a 2010 Chevrolet Malibu into the rear of parked trailers.

The goal wasn’t to evaluate the Malibu’s crashworthiness. The midsize sedan earns top safety ratings from both IIHS and NHTSA.

“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 a serious threat

Decapitation is a serious threat in underrides. In 3 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.

One such test involved a Hyundai trailer whose underride guard bent forward, sheared its attachment bolts, and broke after the Malibu hit it in the center rear at 35 mph. This was the weakest guard tested. The trailer was manufactured by Hyundai Translead.

In contrast, a Wabash trailer outfitted with a guard certified to Canadian specifications successfully prevented underride of the Malibu’s passenger compartment in a center-rear test at 35 mph. The trailer was made by Wabash National Corp. Its guard was the strongest of the 3 evaluated.

“Strong attachments kept the Wabash guard in place so it could engage the Malibu, allowing the car’s structure to absorb and manage the crash energy,” Lund said. “In the real world, this would be a survivable crash.”

Regs haven't kept pace

The basic problem is that while car safety standards have been constantly improving, underride regulations have basically remained the same, IIHS said.

“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 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 crashwor-thiness,” Lund said. “Absent regulation, there’s little incentive for manufacturers to improve underride countermeasures, so we hope NHTSA will move quickly on our petition.”