Front-seat belts have pretensioners and load limiters

Saturday, July 13th, 2019

Seat belt technology has improved over the years — but only in the front seats, which are now safer than the back seats:

For the sake of comfort, modern seat belts give a little as occupants move. But if a passenger suddenly pitches forward, a mechanism called an inertia-lock retractor will prevent the belt from completely unspooling. This device is used in both front- and rear-seat belts.

“It doesn’t get any tighter,” Mr. Zuby said. “It just stops where it is.”

Front seat belts, though, have two safety features that typically aren’t found in back: a pretensioner and a load limiter.

The pretensioner reels in a seat belt when a vehicle rapidly decelerates, pulling occupants firmly against the seat to prevent them from smashing into the steering wheel or glove compartment. The load limiter causes the belt to loosen slightly if the tension of a passenger launching forward against an unyielding belt reaches a dangerous threshold.

“The idea of a seat belt is twofold,” Mr. Zuby said. “Pretensioners take out slack before the occupant pushes into the belt. Load limiters allow the belt to pay out to make sure the forces that keep you with the car don’t get high enough to injure you, in particular your chest.”

To see what happens in frontal crashes—when seat belts offer the most protection—the Insurance Institute examined injuries to 117 belted rear-seat passengers in collisions that occurred from 2004 through 2015. The occupants in the study, which was published in April, were age 6 or older. The vehicles were model year 2000 or later and were no more than 10 years old at the time of the crash.

Thirty-six of the rear-seat passengers were seriously injured and 81 were killed. More than half were more seriously injured than front-seat passengers in the same crash.


Since then, a 2013 study by NHTSA has found that front-seat occupants of passenger vehicles wearing seat belts with pretensioners and load limiters had a 12.8% lower fatality risk than occupants restrained by front-seat belts without these technologies.


  1. TRX says:

    But-but-but… when they were ramming air bags down our throats, they were telling us we wouldn’t *need* seat belts any more! The Wonder Bags were going to take care of everything!

    Heck, I remember the original seat belt campaigns from the mid’60s. When you buckled up, you created an invisible zone of force that protected you from any possible injury. When people asked why, if seat belts were so wonderful, why did we need air bags? The excuse was that you couldn’t forget (or refuse) them, and the belts would be redundant anyway.

    Of course, most states have laws mandating seat belts whether they’re useful or not, and none require air bags as far as I know… probably for the convenience of the “revenue enhancement officers” who can easily see if you’re wearing your bondage gear, but it can be difficult to tell if a car has functioning air bags without detonating them to see.

  2. Kirk says:

    I’m ambivalent about the whole thing, TBH. I think the benefit of airbags and seatbelts is reduced because of the fact that they tend to make the drivers and passengers overconfident and unheedful of consequence. Leave it to me, and I’d have both, but the overall societal consequences? LOL…

    Two things are going on, here: One, you’re enabling dumbasses to survive really stupid behavior, and I would argue that the long-term effect of that on the gene pool is entirely inimical. Two, you’re encouraging said dumbasses to do really stupid things, because they’re so certain that they’ll survive the wreck due to the safety gear, and that they will then almost certainly kill uninvolved third parties. I remember an accident a few years back where a couple of dumb and drunk teens stole a high-performance car, and managed to wreck it in such a way that they killed an older couple who were sleeping in their bed on the second story of their home… Leaving some other teens orphans. The drivers of the stolen vehicle survived without injury. Due, of course, to the “safety gear” installed in that high-end car.

    It’s a double-edged sword. The other point, too, is that the air bags often cause more injury than they prevent–I’ve got a friend who’s permanently injured because the airbags in his brand-new Mitsubishi activated for no real reason, and caused him to hit a median barrier after the bags deployed–Which was when he got injured. He was basically just driving down the road, the airbags activated when he was going about forty-fifty miles an hour, and the rest ensued.

    Funny thing about that–Mitsubishi settled on that one before it even got to court. The insurance guys went to them for info, they looked into it, and “Here’s slightly under a million dollars, and a non-disclosure agreement…”.

    I don’t think anyone even knows what the hell happened–My friend has no memory of the accident, just the airbags activating. The investigation showed no reason for them to activate, either–No skid marks, no signs of another car hitting him, nothing. Just… “FOOOM”, and then he hit the median barrier right after the bags deflated.

  3. Wang Wei Lin says:

    Kirk… In an accident staying in the vehicle within the designed safe space ‘cage’ gives you the best possible outcome except for the dumbass factor you mentioned. Watch a few unbelted crash videos on YouTube. Decades ago, before airbags, what really nailed it for me were the stories told by a state trooper about his accident investigations. He noted in collisions he would often find unbelted drivers and passengers scattered around the scene dead, dying or severely injured crying for their mommas. In the course of the subsequent investigation he would measure the space where they would be had they been belted. Generally the passenger spaces were preserved enough to save lives injuries notwithstanding. It’s too bad our modern technology is defeating the Darwin effect.

  4. Kirk says:

    Wang Wei… Don’t get me wrong; I’m using both if I can, but I’m also not driving like an idiot in confidence that they’ll save me from all sorts of misadventures. Which, unfortunately, is how a lot of idiots out there treat them.

    There are some things that serve the wise well, yet which are overall detractors for society. Passive safety systems are something I’m ambivalent about simply because they insulate the unwise from the consequence of their poor decision-making skills. Leave it up to me, and I’m gonna remove most “safety features”, and force these people to think about what they’re doing. It’s like ABS on ice; yeah, it helps the neophyte driver, but when you’re an experienced driver who knows how to pulse the brakes properly, it actually detracts from being able to control the car.

  5. Isegoria says:

    I think everyone else should have Tullock’s spike installed.

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