Hacker News Reader

While seat belts work, I think what saved these kids lives were the crumple zones. Those do work twice. If the car crumples in areas that don't impact the riders that's a good thing. Nobody would have survived such a crash in a classic Chevy.

The front of that car is obliterated, but notice the damage ends where the cabin begins. New autos have been receiving upgraded crumple zones for decades because they work. And it looks like Tesla hasn't avoided the issue.

I don't know exactly where the hard parts (cabin) of the Tesla begin and end but it's possible to have enough energy to just barrel right through the crumple zone.

Crumple zones are directional, when you tweak them they lose effectiveness in their primary direction, that's part of why modern cars get totaled by less damage (your insurance doesn't want to pay big $ for medical when you crash again, with less effective crumple zones). The #1 purpose is to buy time for the airbag to explode before the occupant's faces are occupying the area it takes up once inflated. Acting as an energy absorbing barrier is second priority. It's perfectly possible to hit something hard enough that you only get the first functionality out of it. e.g you hit a brick wall so hard that the "oh the front of the car stopped quick, better explode now" logic has time to happen. Even at 100+mph, the time it takes to drive 4ft (the length of the hood) there's plenty of time for the airbag to explode. However, if the car is moving fast enough the "crumple zone" won't slow the car considerably. Imagine the difference between falling out of a second story window into a (freshly plowed) snow bank vs falling out off the empire state building into the same snow bank, sure it still decelerates you but not enough to matter. Based on the spot where the car wend airborne, it wouldn't surprise me if the crumple zone was tweaked making it easier to completely go though.

Crumple zones remove energy making the rest of the accident less dangerous. Air bags operate on a similar principle 1 second post accident most of the speed is gone even if the car is still in motion. In other words survive the 80MPH crash and the secondary 40MPH crash is vastly less dangerous.

PS: Sure, there are a tiny fraction of edge cases such as falling off a cliff where it's a longer term problem, but it's reasonable to ignore them.

> Forget the fancy safety features. The humble belt is more important than all of them put together.

Totally agree with the second sentence, but disagree with the first. It's not like these features are just thrown in for fun; there is research and testing behind them, and they do save lives.

It's like that oft-misquoted statistic that you lose 50% of your body heat through your head. In reality that's only true if you cover the rest of your body with clothes, but leave your head bare. Obviously wearing clothes is going to keep you warmer than wearing a hat. But, if it's cold out, it does make sense to put a hat on too.

> It's not like these features are just thrown in for fun; there is research and testing behind them, and they do save lives.

Exactly, but some of them are designed to be paired with a seat belt - I've heard that airbags can make things worse if you don't buckle up.

The NHTSA has a few videos showing exactly this.

Many of those features, particularly the early airbags, markedly improve safety only where the seatbealt isn't used. That was and still is a norm in the US, but in places like Europe or Canada where seatbelt use is near universal, the advantage is minimal. The costs (1000s) are not minimal. So some would say that removing the airbags and spending that money on other things (ie crash prevention) might be the more efficient approach to safety.

It gets really interesting with cars that have no crumble zone - like the Smart. They managed to build that little devil in a way, that the motor gets partially shoved beneath the floor of the car..

At least shock-absorbing seatbelts can absorb the first (and probably stronger) shock and act as a normal seatbelt after that. So I don't understand what is the point to be against that.

To absorb the first shock they have to lengthen. To act as a normal seatbelt afterwards again, they would have to shorten again to properly restrain you. They might not have enough time for that.

(All just speculation.)

Wouldn't the shock-absorbers still at least retain someone after being used once? I gathered that regular seatbelts will have to be replaced after an accident anyway, they too stretch a little in an accident without retaining their stretchiness.

To clarify this: flip implies end over end rotation where as roll implies side over side rotation. Therefore, it takes considerable more force to flip a car than it does to roll it.