Comment by mkmk | Hacker News Reader

Comment by mkmk | Hacker News Reader

Parent Full thread

This feature once saved me from what would have otherwise been a very nasty crash, many years ago.

I was driving too fast in a borrowed car over a small hill and hadn't realized that traffic had stopped just out of my sight until too late. I heard a beep and saw flashing on my dash and I started braking but a moment later the emergency braking system kicked in, braking much harder than I would have been able to. The car stopped, hard, a foot or two short of the pickup truck in front of me.

As the brakes kicked in, my seatbelt tensioned and pulled me into my seat, which was surprising because, although I had a vague idea of emergency braking, I didn't know the seatbelts would do that. And although I may be mis-remembering since this was so long ago, it feels like the passenger seat next to me started moving (I'm not sure why) – I should look that up.

Made me infinitely grateful for the engineering that went into this system. I was quite young and insufficiently cautious, and it was an eye-opening experience.

Seatbelt tensioners are life savers. They're a little explosive charge under the chair near the seatbelt attachment point that yanks hard on the belt to squeeze you against the chair while the car comes to a stop. They're super powerful and you don't want to mess with them unless you know exactly what you're doing (see also: airbags).

Interesting! My recollection was that it was a non-explosive tensioner, but maybe I'm wrong. Thinking about explosive tensioners reminds me of an EOD tool I recently learned about – the rocket wrench. https://www.youtube.com/watch?v=11qa5LFB6zI [1:36]

There are spring loaded ones too but they're not as powerful or as fast.

https://laughingsquid.com/a-slow-motion-video-of-a-pyrotechn...

Hm I think it was something else entirely. If I recall correctly, it felt like a motorized ratchet pulling me back in my seat.

Was that a VW? Sounds like their PreCrash system. When it detects impeding collision, it tensions seatbelts and closes windows.

So do you have to replace the explosive even if you don't end up crashing?

If it's an explosive one, yeah.

> the emergency braking system kicked in, braking much harder than I would have been able to

So this is completely not true. You can brake as hard as any system can, there's no magic to it. Just press on the brake pedal hard, in any ABS car.

Surprisingly, this is something people often don't do. I am an instructor at car control clinics, one of the exercises is panic braking. All you need to do it press on the brake pedal. Easily 50%+ of students struggle with this. Just press hard. That's it.

Also, please take car control clinic. It will save your life and those around you.

I believe that the statistics are that most people don't brake anywhere near hard enough in accidents, because you're just not used to pushing the pedal that hard.

Yes this is what we see in the car control clinics.

I've been involved in these since the 90s. Back then the braking exercises were about teaching threshhold braking since most cars didn't have ABS.

I speculated that once ABS becomes mainstream we'll need to remove these exercises from the classes since there won't be anything left to teach, just press the brake and the car will do all the work.

I never foresaw that "just press the brake" was going to be so difficult for so many people that the braking exercises are still to this day very useful and most people fail badly the first few attempts!

For anyone reading, if you've never braked hard, braking hard in an ABS car means push on that brake pedal with the full force of your leg muscles as hard as you possibly can and then keep that pressure on, don't let go.

(Also, please sign up for a car control clinic.)

In the UK the driving test includes an emergency stop which means everyone has to learn to do one. It definitely is surprising the first time you do one. It's worrying that there are drivers out there who haven't done one and don't even think they are capable of doing it when necessary.

Yes, unfortunately in the US getting a driving license does not include any car control training. It is really criminal negligence by the part of the government/DMV.

> braking much harder than I would have been able to

Any idea why you weren't able to apply full brakes? I remember reading that most people don't in an emergency and that's why the emergency brake boost was created, but haven't seen the reason for it.

This is just one of those suspicions I have had for many years and done nothing to verify, but I think part of it is probably that everyone sits too far back from the pedals.

I have my seat adjusted so that with my back and butt against the back of my seat (so I’m braced against something) I can push the brake pedal and have it hit the bottom of travel just a bit before my knee locks without having to take my heel off the floor and try and press it with my toes or something.

My wife is almost a half foot shorter than me and when I drive her car I don’t need to adjust the seat at all. I find a similar situation driving most people’s cars.

So, y’know, I think people literally can’t apply the brakes all the way… because they can’t reach the bottom of the pedal travel.

I suspect it's more like people brake at first like a startle reflex, but they only brake really hard once their brain does the calculus and full panic sets in. Then they can bend the brake pedal.

On a motorcycle this is actually a lifesaver that's a very natural reflex because you want to load the front suspension and tire before you almost lock it up.

I'm not sure what the exact amount of force is, but I took a more performance oriented driving course that included some hard braking at highway speeds.

It's fairly violent. In normal driving we never do this, it would cause someone to rear end you and it's not necessary. So we have lots and lots and lots of practice braking at a moderate pace. Braking fast in normal day to day life is maybe a 70% force. We're used to trying to think how much pressure is the right amount of pressure.

What they told us is basically to try to break the pedal off. I think it's the easier way to remember, if the crap hits the fan, just put your foot through the floor and get stopped. The less thinking and modulating, the better.

To add on, most people have never experienced what “full braking” is in any car since it is so uncommon to even use half of the ultimate braking power a car can deliver in a non-track day or non-emergency situation. Even a modern Toyota Camry can sustain on average >1 g of deceleration force from 70 mph to 0.

Thus, people think they have applied full brakes but in reality they are only 60-70% of the way there.

Maybe people who learned to drive on pre-ABS cars?

I can remember clearly my thoughts during before bumping into someone in front of me: it was quick alternates between “BREAK NOW” and “beware slipping”. Traffic was quite slow but but I was terrified to not being able to choose what voice to listen in my head, it was a very strange dissonance experience.

I braked too softly and ended up in the bumper of the car in front of me. The rental car did had ABS and I knew it but didn’t thought of it during the breaking.

in panic mode brain doesnt work well

I've had two situations where it prevented me rear-ending someone.

The system also had several misfires, like when there were cars parked on the curb on a long turn, but mine in particular doesn't start braking until I do - it just beeps and makes the dashboard light up in red.

It's pretty reliable and I would be all for mandating at least this basic implementation.

Reply on news.ycombinator.com