Cars vs. SemiTrailers – Rear Underride Crashes. Five North American semitrailer manufacturers earn the Insurance Institute for Highway Safety’s new TOUGHGUARD award recognizing rear underride guards that are designed to prevent a range of deadly underride crashes. Semitrailers from Great Dane, Manac Inc., Stoughton Trailers LLC, Vanguard National Trailer Corp. and Wabash National Corp. earn the accolade.
An underride guard is the metal bumper that hangs from the back of a semitrailer. The idea is to stop a smaller vehicle from sliding beneath a high-riding trailer in a rear-impact crash to preserve survival space for the people inside the lower riding vehicle. All underride guards must meet federal safety standards, but IIHS research and crash tests have shown that many underride guards can buckle or break off in a crash. When guards fail, the resulting underride crashes often result in death or serious injury to people in passenger vehicles.
The IIHS TOUGHGUARD winners have rear guards that prevent underride of a midsize car in three test modes – fullwidth, 50 percent overlap and 30 percent overlap. In each configuration, a midsize car travels at 35 mph toward a parked semitrailer. In the full-width test, which is the easiest to pass, the car strikes the center of guard head on. In the 50 percent overlap, half of the car’s front end strikes the guard. In the toughest test, 30 percent of the front of the car strikes the trailer at its outermost corner. Underride guards are weakest at the outer edges of a trailer.
The TOUGHGUARD award is the culmination of six years of IIHS research and testing. The Institute began its underride crash test program in 2011 and has since evaluated multiple trailers from eight of the largest trailer manufacturers in North America.
In the initial round of evaluations, the guards on all of the semitrailers prevented underride in the full-width test. In the 50 percent overlap, 7 of 8 guards prevented underride. In the 30 percent overlap, only Manac’s guard stopped the car from underriding the trailer. Great Dane, Stoughton, Vanguard and Wabash subsequently reworked their designs and asked for retests.
The manufacturers used different countermeasures to toughen their guards. Stoughton, Vanguard and Wabash added vertical supports to the outboard edges, while Great Dane added larger fasteners to existing vertical supports to reduce the chances that the supports would be torn from the trailer. Great Dane also increased the size of the lower horizontal member of the bumper, which made it stronger. The new Great Dane design is the latest to be tested.
All of the changes manufacturers have made exceed current rules in place in the U.S. and Canada, as well as proposed new requirements from the National Highway Traffic Safety Administration that would essentially align U.S. underride regulations with Canadian ones.
Semitrailers from Hyundai Translead, Strick Trailers LLC and Utility Trailer Manufacturing Co. have passed the full-width and 50 percent overlap tests but not the 30 percent overlap evaluation. These three manufacturers are working on improvements, and IIHS will evaluate the new designs when they are available for testing.
In 2015, 427 of the 2,646 passenger vehicle occupants killed in large truck crashes died when the fronts of their vehicles struck the back of trucks. That is up 39 percent from 2011 when 260 of the 2,241 passenger vehicle occupants killed in large truck crashes died in impacts with the rear of a large truck. Gaps in federal crash data make it difficult to pinpoint exactly how many of these crashes involve underride. In a 2012 IIHS study of fatal crashes between large trucks and passenger vehicles, an estimated 15 percent involved the rear of the truck. An IIHS analyses of a smaller sample of fatal crashes found that 82 percent involving the rear of the truck produced underride.
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