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These days, most vehicles are designed so that, if you get into a crash at about 35 mph -- even if you run straight into a solid, immovable wall -- you're likely to walk away. But recent crash tests and an analysis by the Insurance Institute for Highway Safety concluded that if you crash into the "underride guards" on the backs of tractor-trailers at that speed, the consequences can be deadly.

These rear guards are the primary countermeasure for reducing deaths and injuries when a passenger vehicle crashes into the back of a tractor-trailer, says Adrian Lund, IIHS president.

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 those large trucks and trailers that are not currently required to have them.

In 2009, 70 percent of the 3,163 people who died in all large truck crashes were occupants of cars or other passenger vehicles, Lund said. In many of these crashes, the upper part of a passenger vehicle's cabin was crushed when the body of the truck or trailer smashed through the vehicle's safety cage.

"The way passenger cars are designed, if you crash into another passenger car, the front-end structures can withstand and distribute a tremendous amount of crash energy, in a way that minimizes injuries for vehicle occupants," says Lund. "But hitting the back of a large truck is a totally different situation. Your vehicle could be one that earns top marks in frontal crash tests, but if that truck's underride guard fails -- or if the truck doesn't have one at all -- your chances of walking away from even a relatively low-speed crash are not good at all."

In the Institute's recent study, it took case files from the Large Truck Crash Causation Study -- a federal database of roughly 1,000 real-world crashes in 2001-03 -- and analyzed them to identify patterns of crashes involving heavy trucks and semi-trailers with and without underride guards. Only 22 percent of those crashes either didn't involve underride, or had only negligible effect. 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) estimates that about 423 people in passenger vehicles die every year when their vehicles strike the backs of large trucks, and that more than 5,000 passenger vehicle occupants are injured in such crashes.

Based on that data, the Institute conducted crash tests at various speeds to gauge how serious the injuries to passengers could be at those speeds. The Institute's crash tests evaluated three semi-trailer rear guards that comply with current U.S. government regulations. Two of the trailers were also certified to meet Canadian requirements, which are more stringent than U.S. regulations when it comes to strength and energy absorption. In the tests, a 2010 Chevrolet Malibu was crashed into the rear of the parked trailers.

Lund stresses that the purpose was not to assess the Malibu's crash-worthiness. The Malibu has already earned a Top Safety Pick designation from the Institute and got a 5-star safety rating in the National Highway Traffic Safety Administration's New Car Assessment Program.

"The purpose was to ascertain if some underride guards perform better than others, and to find out what crash speeds and underride designs produced different types of failure," says Lund. "The damage to the cars in some of these tests was so devastating that it's hard to watch the footage of the tests without wincing. If these had been real-world crashes, there would be no survivors."

Decapitation is a very real possibility in underride crashes. In three of the crash tests the heads of the dummies in the car either smashed into the trailer or into the car's hood after the hood was ripped off and was pushed into the occupant compartment. One such test involved a Hyundai Translead 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 of the guards that were tested.

Meanwhile, a trailer made by Wabash National Corp., which was equipped with a guard that met Canadian requirements, successfully prevented underride of the Malibu's passenger compartment in a center-rear test at 35 mph. The Wabash's guard was the strongest of the three that were tested. A trailer made by Vanguard National Trailer Corp. ranked in the middle.

"The Wabash trailer had strong attachments, which is what kept the guard in place," says Lund. "As a result, the guard engaged the Malibu's front end, which allowed the car's structure to absorb the crash and distribute the energy of the crash. If that was a real-world incident, that would have been a survivable crash."

The Institute also conducted tests with overlaps of 50 percent and 30 percent to discern what would happen if a car crashed into the trailer with only part of its front end instead of a full head-on crash.

In a 35-mph test with a 50 percent overlap, the guard on the Vanguard trailer allowed severe underride. Its guard meets both U.S. 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 end of the guard that was struck in that 30 percent test bent forward, allowing for significant underride.

This test showed that even the strongest guard leaves as much as half of the rear of the trailer vulnerable to severe underride, says Lund, adding that the guard only worked as intended when the striking car engaged the center.

"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 the guards on their trailers. We think all guards should be evaluated this way. At the very least, all rear guards should be as strong as the best one we tested.

"Absent regulation, there's little incentive for manufacturers to improve underride countermeasures," concludes Lund. "So we hope NHTSA will move quickly on our petition."


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  • 487 Comments
      • 4 Years Ago
      How 'bout if people learn not to follow so close.
      neal
      • 4 Years Ago
      hey, pay ATTENTION while driving you idiots!!! or, get OFF the road!
      bkoster2
      • 4 Years Ago
      It's obvious that many of you have no clue .....but you're still an expert on this subject. Maybe you've had a bad day or a close encounter with a truck at some point.....neither will help you here. IF you haven't driven a truck and been subjected to every kind of idiot driver already, you have no business responding. IF you HAVE driven a truck for a living for any length of time you'd have had plenty of opportunities to see first hand what i'm talking about. NObody is reponsible for anything other than the vehicle that THEY are driving....period. IF I crash into the truck ahead of me....it's MY fault...not the trucks ....not the truckdriver! When they make all vehicles idiot proof, then and only then, will this stop. However try as they might, making anything "idiot proof" isn't working quite like they hoped it would.....least of all a vehicle...car or truck! The old saying is "you have to be smarter than the machinery"...and many have already proven they aren't. Sorry folks....time to take responsibility for your own actions and stop trying to blame someone else.
      jh
      • 4 Years Ago
      I drive a truck and have never had an accident period due to my fault and it pisses me off that normal people not truck driver usualy cause the accidents. I have had several people drive under me in cars while they are texting or reading the paper or a book. Im sure some trucker fresh out of school especially the young one cause accidents by not having enough experience. But the main problem with 4 wheelers is they ride right beside a truck or tail gate us that will get you killed,let my steer tire blow or a cap on trailer blow-it can and may come thru your winshield a kill you. So you can cut the 17 hour a day working trucker some slack and say thanks for getting my food-tv-building materials to the store so i can buy it. You can all so thank obama for negelecting the middle east and causing the fuel prices to go up so your tv-and food are going up now while my pay check goes down due to fuel cost.jh
      • 4 Years Ago
      @Tglenton1...what a waste of good air you are.
      • 4 Years Ago
      Dont blame the trucks design, pay attention, dont hit the truck
      • 4 Years Ago
      Main cause and almost everybody does this. TAILGATING !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
      • 4 Years Ago
      The problem is the newbe truck drivers comming out of truck driver school try to drive a rig like a car they need to slow down, and they got to learn you have to always give the cars the right of way because they dont know any better.I always give cars alot of room away from me.I never would tailgate a car with a truck.Because that could be my daugher or wife driving that car that the truck is tailgating.Also I dont think these truck driving schools teach these drivers how to shift a 18,13 or super 10 speed transmission they learn the drive in auto trans and they sure cant back up either I dont know how many times I had to get out of my truck to back up for a new truck driver who couldnt they just give them a CDL and put them out there.No wonder there are so many crashes lately.
      qegalpal
      • 4 Years Ago
      I know a few truck drivers and they are some of the safest drivers out there. truckers are almost always the ones getting cut off by some azzwipe trying to stay ahead of everyone else on the road to get the first. meanwhile the poor trucker with a full and HEAVY load is trying to slow down fast enough to keep from killing him, anyone else or up-setting his load. the only thing I have against truckers is their use of re-treads. I wish there was a statistic for how many people are killed by re-treads exploding off a truck and or hitting/trying to avoid the debris they leave behind, aka road gators.
      • 4 Years Ago
      Come on guys. We all know ********* almost always the 4 wheelers fault if it ends up under your rig, but I've had a few close calls and I really don't want to have to jump out of my cab and try to pry somebodies family out from under my trailer. Of course the problem would go away if all drivers followed the rules, ******** not going to happen. If some lives can be saved for a few hundred dollars, why not. The next idiot that gets pulled out from under a trailer could be your son or daughter.
      • 4 Years Ago
      So why if the article is about the rear guards on big truck did they post a picture of the front of a truck?
      • 4 Years Ago
      The problem is following to close and the under ride guard not going down far enough because the auto industries changed th car designs if you change the guard to fix the lower cars the suv s will suffer .......make the under ride on the vehicles that cause and have been changed .....BET IT WON"T BE A BIG ENOUGH PROBLEM TO DO THAT -------JUST SHOVE IT OFF OFF ON AN INDUSTRY THAT CAN'T AFFORD IT !!!!!
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