Seatbelts - Sorta Kinda Work? Or Almost Perfectly Reliable?

[fessie]

There’s a youtube segment that’s been making the rounds today. Apparently their 3-yr-old boy died in a rollover car accident because his 3-pt seatbelt failed, causing him to be ejected from his family’s van. I believe he was in a booster seat appropriate for his height and weight, as mandated by law, but honestly I’m not sure since I can’t bear to watch the whole thing.

Their point is that small kids need to be in 5-pt harnesses instead.

Anyway, the author of the clip states

Kyle’s seatbelt came unlatched during the roll and he was ejected. His seatbelt was later examined by several experts who determined it was faulty and told me that seatbelts regularly fail, especially in roll over accidents.

I’m like - huh? I thought seatbelts were supposed to be just about perfect.

I tried the googles and found a whole lot of lawyers who’d be glad to represent me if I or my family have been injured in an automobile accident. One of them did have some interesting data:

@steven laird

In the late 1970S, NHTSA opened an engineering analysis based on allegations that some buckles would release when they were subjected to a sharp blow on the front or back. Subsequent testing by the NHTSA Office of Defect Investigation was conducted to determine the vulnerability of seat-belt latching mechanisms to inadvertent latching. Tests of 225 American cars manufactured over an eight-year period showed that 50 buckles opened inadvertently. Where an individual has been injured in a collision and it appears that he was not wearing the belt post-crash, yet eyewitnesses confirm he had buckled up, he may be the victim of a poorly designed latching mechanism.

Isn’t that a 22% failure rate? Doesn’t that seem rather high?

The NHTSA has a lot of data concerning parents’ failure to use restraining systems properly, but I didn’t see any mention of seatbelts themselves failing.

So I’m wondering - did these parents contribute to their child’s demise by not restraining him properly? Or do seatbelts fail frequently?

Or was this family just spectacularly unlucky?

[Askance]

225 cars = 1125 buckles, 50 (4.7%) of which (according to the 30 year old report) failed “when they were subjected to a sharp blow on the front or back”. If it were true I guarantee that the design of the buckles would have been modified accordingly; maybe that’s why the buckles are mostly down by the sides of seats these days.

[commasense]

I’m not an automotive engineer, but I do have a little more experience with auto safety issues (theoretically, at least) than the average man on the street.

Where to start? First, I wouldn’t take at face value anything that a lawyer says on a Web site intended to drum up business.

Second, I think you may have misinterpreted, or the site have have mischaracterized, the study. Specifically, I don’t think the interpretation that led you to the 22% figure is accurate. I suspect that it’s saying that in a study that covered 225 different models (not 225 cars) 50 belts failed. (I grant that I could be wrong about this.) In any case, as askance pointed out, it’s from 30 years ago, and technology has advanced.

Third, rollovers are a relatively rare form of accident, and the three-point belts that work well in the vast majority of collisions can’t be expected to offer perfect protection when the car goes upside down. All engineering represents a compromise between many factors, such as expense and durability, or convenience and effectiveness. The three-point harness was shown to be much more effective in preventing injury than a simple lap belt, while still being simple and quick to get in and out of.

A five-point harness would undoubtedly offer more protection, but as the owner and user of one in my track car, I can tell you that you wouldn’t want to have to use one on a regular basis. Instead of taking about three seconds to reach over and snap a single connection, it takes about a minute to snap in all the latches and tighten down the lap and shoulder straps of a five-point system. Also, it completely restricts your ability to move in the seat. Just what you want in a race car, but not exactly ideal when you need to reach over and get something out of the glove box. So five-point harnesses are just not a reasonable compromise for ordinary street driving.

Furthermore, even if you wanted to mandate five-point harnesses just to prevent injuries or deaths in rollovers, you’d have to go further and significantly strengthen the roof. This is a point of contention among amateur autosports enthusiasts like myself, because some people install harnesses in their cars for the added control they get from being tightly strapped to the seat, without going the next step and installing a roll bar.

Once you’re strapped into your seat with a five-point harness, if you do roll onto the roof, your head and neck will be held firmly in place as the roof collapses on you. If you’re wearing a three-point belt, you can bend over sideways and, with a little luck, not break your neck or crack open your skull. So a five-point harness without a substantially stronger (i.e. more expensive) roof structure would be worse than a three-point and weak roof.

I don’t have much info on child safety seats, so the parents’ choice of seat, or the way they used it, might have contributed to the tragedy. But if not, they were just very unlucky.

[fessie]

Thank you, commasense, for sharing your expertise.

And obviously you’re both correct, I misunderstood the statistics - although doesn’t it still demonstrate that in 20% of accidents involving a carload of people, one person’s seatbelt would fail? I realize those data are old, but I couldn’t find anything else.

The 5-pt harness is really only a viable option for parents of small children, who are faced with a baffling array of seating options when they go shopping.

It was the parents’ offhand quote “seatbelts fail all the time” that really threw me. Now we moms have one more thing to fret over - and this one really IS a threat; children of all ages are far more likely to die in a car accident than from being snatched by a stranger from their backyards.

[Richard_Pearse]

@commasense

Also, it completely restricts your ability to move in the seat. Just what you want in a race car, but not exactly ideal when you need to reach over and get something out of the glove box.

There’s no reason why the shoulder straps couldn’t be on an inertial reel. But ultimately, you’re right, it would result in more people not wearing the belts all together. The benefit of a stronger seat belt may be out-weighed by less people bothering to wear them.

[Hypno-Toad]

Three point seatbelts have saved me from death or permanent injury twice. I don’t plan on giving them up any time soon.

[ethelbert]

I believe many of the allegations of seat belt failure have to do with the buckle becoming unlatched during an accident due to poor design of the buckle. Some buckles were originally designed with buttons that protruded from the case. During an accident, the button would come in contact with part of the car or body and the latch would release. A study done many years ago might reflect the higher failure rate of the early buckles. However, even the best designed buckle might unlatch during an especially violent accident.

If you enter ‘seat belt defects’ into google, you will find many sites, all of them from law firms, that detail some of these problems.

[Rick]

The three point seat belt is the single most effective safety item ever to be installed in a car period.
However with that said, you have to recall that every time a person gets into a car they have to fasten the belt. It is possible on some belts to get the tounge almost into the buckle and think that it is buckled. Also when dealing with a child there is always the possibility that the child will play with the buckle while driving. I know my kids each did this a time or two, until they learned that if they unfastened their belt, I stopped the car and waited.
Can a belt fail? Sure. Any mechanical thing more complex than a crowbar can fail. Do they fail very often? No. In our sue happy society no car maker could afford to make a car had regular seat belt failures. Is there a difference in failure rates between car makes? Probably.

[mlees]

Also, the seat belt needs to be properly adjusted for the passenger, I presume.

My threepoint belt, which snaps from left to right, crosses over and rests on my left coller bone. I wonder if, in an accident, I would get choked or my larynx crushed. (I have been in one serious accident a year ago. Seat belt from the car prevented injury.)