The Insurance Institute for Highway Safety is always looking for new ways to make America's highways safer, and this latest test checks out the crashworthiness of one of the most overlooked vehicles on the road: tractor trailers. Pointing out design flaws inherent in semi trailers during rear-end collisions, the IIHS performed three different tests on eight of the most popular semi trailers on the market including a full-width impact, a 50-percent overlap (where only half of the car makes contact with the trailer) and a narrower overlap where only 30 percent of the car hits the trailer.

In the tests, which were run at 35 miles per hour using a 2010 Chevrolet Malibu, all of the trailers safely prevented the vehicle from underriding – going underneath the trailer – during the full-width crash. Compared to the results from this same test just two years ago, it's a big improvement in safety. In the 50-percent test, only one of the trailer's underride guards failed allowing the rear edge of the trailer to impact the passenger compartment, which would have most likely killed the driver. In the 30 percent overlap test, only one trailer managed to prevent the crash car from going under the trailer. The safest trailer, produced by a company called Manac, had the underride guard beams pushed out to the edges of the trailer providing additional strength and support. All of the trailers passed US and Canadian crash standards.

Scroll down for the crash-test video as well as a press release from IIHS.


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New crash tests: Underride guards on most big rigs leave passenger vehicle occupants at risk in certain crashes

ARLINGTON, Va. - Modern semitrailers for the most part do a good job of keeping passenger vehicles from sliding underneath them, greatly increasing the chances of surviving a crash into the back of a large truck, recent tests by the Insurance Institute for Highway Safety (IIHS) show. But in crashes involving only a small portion of the truck's rear, most trailers fail to prevent potentially deadly underride.

Most semitrailers are required to have underride guards. These are steel bars that hang from the backs of trailers to prevent the front of a passenger vehicle from moving underneath during a crash. Earlier research showed that the minimum strength and dimensions required for underride guards are inadequate, prompting the Institute to petition the National Highway Traffic Safety Administration (NHTSA) in 2011 for tougher standards. The Institute also asked the agency to consider applying the standards to other types of large trucks such as dump trucks that aren't required to have any underride guards.

Although NHTSA hasn't responded yet, trailer manufacturers already are installing guards that are much stronger than the agency requires. These guards generally work well to prevent underride, except in crashes occurring at the outer edges of trailers, the crash tests show.

One likely reason manufacturers are installing guards that are stronger than required is a tougher standard that trailers in Canada have had to meet since 2007. More recently, IIHS crash tests have drawn attention to the issue, and at least one manufacturer has started selling a trailer with an improved underride guard since the tests began.

To see how well the latest guards work, IIHS engineers put trailers from the eight largest manufacturers through a series of progressively tougher crash tests. All of the trailers had underride guards that met both U.S. and Canadian standards. Both standards require a guard to withstand a certain amount of force at various points. Under the Canadian regulation, a guard must withstand about twice as much force as required by the U.S. rule at the point where it attaches to its vertical support.

In each crash test, a 2010 Chevrolet Malibu struck a parked truck at 35 mph. In the first scenario, the car was aimed at the center of the trailer. All eight guards successfully prevented underride, including one from Hyundai Translead, whose previous model failed a full-width test by IIHS. In the second test, in which only half the width of the car overlapped with the trailer, all but one trailer passed. However, when the overlap was reduced to 30 percent, every trailer except one from the Canadian manufacturer Manac failed. Manac sells dry van trailers in the U.S. under the name Trailmobile. The Institute uses a 30 percent overlap for the most challenging underride test because it is the minimum overlap under which a passenger vehicle occupant's head is likely to strike a trailer if an underride guard fails.

"Our tests suggest that meeting the stronger Canadian standard is a good first step, but Manac shows it's possible to go much further," says David Zuby, the Institute's chief research officer.

The danger of underride

All the improvements in occupant protection that have helped drive down crash deaths in recent decades count for little when the front of a passenger vehicle ends up under a truck. When this happens, the top of the occupant compartment gets crushed because the structures designed to absorb the energy of a crash are bypassed. The airbags and safety belts can't do their jobs, and people inside can experience life-threatening head and neck injuries.

The crash tests show how this occurs. The 2010 Malibu was an IIHS Top Safety Pick, and in the 40 mph moderate overlap barrier test used to evaluate the Malibu's frontal crashworthiness, measurements recorded by a dummy in the driver seat indicated serious injuries were unlikely. Similarly, in the underride tests in which the guards held up, the Malibu's structure and airbags protected the dummy, and injury measures were generally low and not life-threatening. In contrast, when the guards failed, head and neck injury measures were so high that real drivers would have died.

In 2011, 260 of the 2,241 passenger vehicle occupants killed in large truck crashes died when the fronts of their vehicles struck the rears of trucks. That's down from 460 out of 3,693 in 2004. The decline is likely due in part to changes in both truck and passenger vehicle traffic resulting from the weak economy.

Gaps in federal crash data make it difficult to pinpoint exactly how many of these crashes involve underride. A 2011 IIHS study of 115 crashes in which a passenger vehicle struck the back of a heavy truck or semitrailer found only about one-fifth involved no underride or negligible underride. Nearly half of the vehicles had severe or catastrophic underride damage, and those vehicles accounted for 23 of the 28 fatal crashes in the study.

Crash test results

The Institute previously released the results of an initial round of crash testing on three semitrailers conducted in 2010 and 2011. The weakest guard tested at that time was from Hyundai. It met the U.S. standard for strength but not the Canadian one. When the Malibu hit the center of the Hyundai trailer at 35 mph in a full-width crash, the guard broke, resulting in catastrophic underride. In 50 percent overlap tests, the underride guard on a Vanguard trailer allowed moderate underride at 25 mph and severe underride at 35 mph.

In contrast, a Wabash trailer had no underride in either the full-width or the 50 percent overlap test. However, when the Wabash was put through a 30 percent overlap test, the underride was catastrophic. That's because the Malibu hit the guard outside its vertical attachment bar, causing the unsupported end of the guard to bend forward. The Wabash underride guard hasn't been redesigned since then.

Since the initial evaluations, IIHS tested Hyundai and Vanguard trailers again after those companies made changes to their underride guards. Trailers from five more companies also were tested. All eight manufacturers now have underride guards meeting the Canadian standard, and none of the current designs had any difficulty passing the full-width test.

Most passed the 50 percent overlap test, too. The exception was the Vanguard. The guard's vertical support broke off the trailer when the guard was hit by the car, just as it did in the test of the previous design.

"Vanguard's older and newer underride guards were certified to the Canadian standard, so clearly the Canadian regulation, while an improvement over the U.S. rule, isn't stringent enough," Zuby says. "Failing the 50 percent test is a big problem because in our analysis of real-world crashes with the rears of trucks, about half of those with severe underride had overlaps of 50 percent or less."

Although the rest of the trailers passed the 50 percent overlap test, most had the same difficulty with the 30 percent overlap that the Wabash trailer experienced in the initial round of testing. The problem stems from the location of the underride guards' vertical supports. On most trailers, the supports are attached to the slider rails, which run lengthwise under the trailer and allow the position of the wheels to be changed depending on the load. Using this structure as the underride guard's attachment point means the vertical supports are located an average of 28 inches from the trailer's edge.

Manac, the only trailer to pass the 30 percent test, takes a different approach. The supports of its underride guard are attached to a reinforced floor and spaced just 18 inches from the edge. The Malibu and the dummy inside it not only fared better, but the Manac trailer also had damage estimates among the lowest of all the trailers. It required only a replacement underride guard.

"If trailer manufacturers can make guards that do a better job of protecting passenger vehicle occupants while also promising lower repair costs for their customers, that's a win-win," Zuby says. "While we're counting on NHTSA to come up with a more effective regulation, we hope that in the meantime trailer buyers take note of our findings and insist on stronger guards."

The Insurance Institute for Highway Safety is an independent, nonprofit scientific and educational organization dedicated to reducing the losses - deaths, injuries and property damage - from crashes on the nation's roads. The Institute is wholly supported by auto insurers.


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    • 1 Second Ago
  • 66 Comments
      56Jalopy
      • 1 Year Ago
      Good use for Malibu's!
        Dean
        • 1 Year Ago
        @56Jalopy
        The Malibu may not be anyone's favorite car, but it probably gets someone to and from work reliably, and safely, so that they may pay taxes, which in turn helps provide you with those welfare checks, so you can sit at home in your mom's basement all day long surfing the internet.
          S.
          • 1 Year Ago
          @Dean
          "It's a a Jump to Conclusions mat. You see, it would be this mat that you would put on the floor... and would have different CONCLUSIONS written on it that you could JUMP TO."
      canuckcharlie
      • 1 Year Ago
      scary stuff!
      Tigaros
      • 1 Year Ago
      how about those yellow school busses...there is no way one would walk away from a crash with them
        S.
        • 1 Year Ago
        @Tigaros
        How do you rear end a 15 foot tall, bright yellow vehicle with bright flashing lights unless you're completely stupid (or driving distracted)? They don't exactly stop on a dime...
        xspeedy
        • 1 Year Ago
        @Tigaros
        The problem is those are really trucks with a big bus body on them.
      bleexeo
      • 1 Year Ago
      Dang, those narrow overlap collisions are BRUTAL!
      Eta Carinae
      • 1 Year Ago
      this is why i dont ride behind trucks.......i try to get pass them as quick as possible
        The_Mell
        • 1 Year Ago
        @Eta Carinae
        "as quick as possible" Nice idea. But what if the big rig does an evasive maneuver just in that moment you want to pass? *bamm* While the best way to handle effects of an accident is to prevent it, there is no guarantee to be able to do so. That's why we need to have safety measures like seat belts, airbags and strong(er) underride guards...
          S.
          • 1 Year Ago
          @The_Mell
          Giving semis adequate distance, keeping your eyes on the road, not hanging in their blind spots, etc. That's how you prevent accidents. You can't keep legislating for these odd "what if" situations if drivers aren't going to take responsibility for their own safe driving.
      dss10
      • 1 Year Ago
      Why, with all of the research that the IIHA does and the resulting implementationn of their safety recomendations, does insurance rates continue to go up?
        RJC
        • 1 Year Ago
        @dss10
        They like the money. And that's not sarcasm.
        BipDBo
        • 1 Year Ago
        @dss10
        Perhaps it's just inflation. Newer, more expensive cars are more expensive to repair. Health care costs have skyrocketed, and therefore, so has liability. Despite inflation in general, my rates have gone down in the 15 years that I've been with Allstate. Sorry to hear yours keeps going up. Perhaps you're just a crappy driver.
        kevsflanagan
        • 1 Year Ago
        @dss10
        Because....fraud and many states have loose regulations if any upon the Insurance industry.
        • 1 Year Ago
        @dss10
        [blocked]
          RWD
          • 1 Year Ago
          Zing! Way to push an unrelated agenda buddy!
      Rich
      • 1 Year Ago
      Everyone needs to drive a Corevette for safety... tucks right on in there.
      Krystal Kid
      • 1 Year Ago
      According to the rear end collision data from the Swedish insurance company Folksam and Autoliv 56% of all rear-end crashes are full overlap and 28% of rear-end collisions have 1/3 to 2/3 overlap. Only 14.2% of rear end collisions would be less then 1/3 overlap and end up hitting the outside edge of this under-ride guard as shown in the video. The under-ride guard on semi trailers is set at 22" measured from the ground to the bottom of the guard. There are more pickup trucks on the highway with bumpers higher then 22" - most you can drive right off the show room floor. So how about an under-ride guard for pickup trucks like those from sparebumper.com? Is the IIHS is barking up the wrong tree?
      Mazdaspeed6
      • 1 Year Ago
      One of my worst fears.
      BlackDog
      • 1 Year Ago
      Ouch!
      lasertekk
      • 1 Year Ago
      A simple (to implement as a law and engineer on the product) uniform bumper height matching requirement --on all vehicles operated on public highways--would eliminate this problem. No excuses.
        Danrar
        • 1 Year Ago
        @lasertekk
        Yep. And any modification to ride height that takes the bumper out of the safe range is illegal. No fines - you get your car impounded - only way to get it back is to pay the impound fee and prove the modification was removed.
          ksrcm
          • 1 Year Ago
          @Danrar
          Where do you think you live? In some kind of free country? No, you get you vehicle expropriated. And if you cry for your loss, it's not that bad - you can still watch it roll around town with D.A.R.E. stickers on it. In its original state.
        fzeppelin
        • 1 Year Ago
        @lasertekk
        Amen!
        Matt44
        • 1 Year Ago
        @lasertekk
        In reality that would never actually work. Vehicles with long overhangs need to be taller so they do not drag on hills. While your idea would work for most tractor trailers because they do not have long overhangs it would not work for vehicles such as school busses. Also, every off road enthusiast would not like these laws because it would make their vehicles no longer street legal because their bumpers need to be higher to stay out of mud and rocks.
          Danrar
          • 1 Year Ago
          @Matt44
          BFD. If you're a true enthusiast tow your monster truck to the site. Of course we all know 70% of the jacked up trucks never see dirt.
          S.
          • 1 Year Ago
          @Matt44
          But he does have a point about the overhangs on buses/semi trailers.
        J.D. McFarland
        • 1 Year Ago
        @lasertekk
        I like the idea, but it would likely result in some strange compromises. You would need an average ride height similar to something like a Nissan Juke (maybe even higher) Most cars would take a hit in fuel economy and off road vehicles would need modifications to meet the new law. Sports cars would end up looking ridiculous. It would save lives, but I doubt it would ever go into effect.
        BipDBo
        • 1 Year Ago
        @lasertekk
        Some of those guards did protect the driver of the car crashing from behind. Some did not. The difference was not in the height. The difference was in the strength of the guard.
      • 1 Year Ago
      [blocked]
        Daniel D
        • 1 Year Ago
        If you read the article you would know this is about doing what can be done to improve the odds. Defy physics? Never mentioned or suggested in the article.
        Rich
        • 1 Year Ago
        If by defying you mean moving the fulcrum, then yes... but you'd be alone on that claim.
        S.
        • 1 Year Ago
        You spelled "gubmint" wrong.
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