crashed chevrolet malibu with roof pillars severely damaged after an impact with a semi trailer
Insurance Institute for Highway Safety semi trailer crash test - Click for high-res image gallery

A new study by the Insurance Institute for Highway Safety has found that underride guards on semi trailers are prone to failure. Despite major advances in passenger car safety since the mid-1970s, it seems the guards on tractor trailers still fail to reliably prevent vehicles from sliding under trailers in the event of a collision – a similar result to studies conducted over 30 years ago.

Of course, some trailers are better than others, but there is no testing standard for evaluating the underride guards and their attachment points and hardware. Despite this, there is a federal safety standard for the guards, and there's also a more stringent Canadian specification that requires the guards to be stronger and absorb more crash energy. In analyzing the Large Truck Crash Causation Study, a federal database of about 1,000 actual crashes from 2001-2003, the Institute determined that of the 115 crashes where a passenger vehicle struck the rear of a truck or semi, nearly 80 percent involved underride, and nearly half of those vehicles suffered severe or catastrophic damage.

The guards aren't required on as many trucks as you'd first think, despite a 1996 standard calling for increased strength, guard size and energy absorbtion. Many trucks are exempt due to their trailer or chassis configuration, with dump trucks being a notable (and notably dangerous) example. When hit straight-on, the guards can perform better than offset tests, but in crash tests, the IIHS found performance was all over the map for trailer underride guards.

The worst performance in these new IIHS tests belongs to a Hyundai trailer whose guard bent and tore from its attachment points in a 35-mph crash test with a 2010 Chevrolet Malibu. Instead of keeping its passengers safe with its high-performing safety design (the Malibu is an IIHS Top Safety Pick), the front of the car slid under the trailer and left the roof structure to absorb the impact with the trailer. A Wabash trailer with a Canadian-spec guard kept the Malibu from plowing under the trailer in the 35-mph center crash test. Offset impacts – when only part of the guard is engaged by a vehicle – are still troublesome, and even the high-performing Wabash trailer suffered severe underride in a 30-percent overlap test.

In light of this ever-present danger on roadways, the Insurance Institute for Highway Safety is callig for more stringent standards, closing the gaps that allow many trucks to go without guards or use guards that don't meet the 1996 standards for strength and energy absorption, and a more comprehensive standard that incorporates a method of better protecting vehicles in offset impacts as well as crash tests by trailer manufacturers to certify that the underride guards and their mounting systems live up to the intent of the law. Full press release after the jump.


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[Source: Insurance Institute for Highway Safety]


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Underride guards on big rigs often fail in crashes; Institute petitions government for new standard
ARLINGTON, VA - New crash tests and analysis by the Insurance Institute for Highway Safety demonstrate that underride guards on tractor-trailers can fail in relatively low-speed crashes - with deadly consequences. The Institute 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.
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," says 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 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.
In the latest study the Institute 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. 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.
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 US 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 is an Institute TOP SAFETY PICK and earns a 5-star safety rating in NHTSA's New Car Assessment Program.
"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 says. "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 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 says. "In the real world, this would be a survivable crash."
Offset tests: The Institute also ran tests with overlaps of 50 percent and 30 percent to find out what happens when a car hits the trailer with only part of its front instead of head-on.
In a 35 mph test with a 50 percent overlap, the guard on a Vanguard trailer allowed severe underride. The trailer was made by Vanguard National Trailer Corp., and the guard is certified to US and Canadian standards. In contrast, the Wabash trailer's guard successfully prevented underride in the same test. The outcome for the Wabash was different when the overlap was reduced to 30 percent. The struck end of the guard bent forward, and there was severe underride.
This test shows that even the strongest guard left as much as half of the rear of the trailer vulnerable to severe underride. The guard only worked as intended when the striking car engaged the center.
Offset tests stress guards' unsupported outboard ends. The vertical frame supports that attach guards to their trailer chassis are closer to guards' centers than ends. Preventing underride in narrow overlap crashes like these might mean devising a new way of attaching guards to trailers to utilize the side rails, in addition to requiring manufacturers to conduct compliance tests with guards on trailers.
"Under current certification standards, the trailer, underride guard, bolts, and welding don't have to be tested as a whole system," Lund says. "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 crashworthiness," Lund says. "Absent regulation, there's little incentive for manufacturers to improve underride countermeasures, so we hope NHTSA will move quickly on our petition."