Hacker News new | ask | show | jobs
by rob74 582 days ago
Hence the "arms race" of ever huger cars, yes. And, if you value your life, don't even think about cycling or going by foot with such cars around...
4 comments

Yes. Anyone who has worked on conservation of momentum problems in high school physics should recognize this. Even at low collision speeds if there is a large disparity in mass between the vehicles then the lighter one experiences a lot of acceleration.

For an extreme case think of a low speed collision between a bowling ball and a ping pong ball.

It boils down to "delta-V".

In a mismatched collision, the smaller vehicle needs to withstand a higher delta-V than the larger vehicle.

Also, in many cases the bumper heights are mismatched so the larger vehicle's strong structure runs into higher, weaker parts of the small vehicle, further exacerbating the problem.

Which is why I'd like a wedge car made to go under a large car in a front end collision.

https://i.imgur.com/xHWAeR4.png

There are several things you can do to dramatically reduce your risk. Cycle during the day, while sober, with bright colors, with a helmet, and avoiding multi-lane roads. If you do these things you've statistical eliminated most of the risk.

> victim blaming

It's an exercise in reducing risk, not assigning blame.

> the law says I can cycle on those roads

The law can't bring you back to life, but if you want to take the risk that's your decision.

We need to think more game theoretically. Since our courageous cyclist must already have a deathwish to be on the same roads as these vehicles, he should go all in with a vest packed with C4 and ball bearings so that, in the event of a crash (which will cripple him anyway), at least he takes out Starbucks Mom on his way to Paradise.
I would wear the hell out of a helmet shaped like a nitro crate from CTR.

https://crashbandicoot.fandom.com/wiki/Nitro_Crate

If the risk is 100x and you eliminate 90% of it, then statistically eliminating most of the risk still doesn't make it all that great a choice.
If you do as I suggest then you eliminate a lot more than 90% of the risk. 62% of cyclist fatalities weren't wearing a helmet, so that alone is a huge thing you can do to improve your odds. 22% are drunk. 50% are on major roads. https://www.iihs.org/topics/fatality-statistics/detail/bicyc...

I knew I would get responses about "why don't cars just..." e.g. why should I change, they're the ones who suck. I'm not suggesting or opposing public policy changes here. I'm giving practical advice which makes cycling much safer than the statistical average.

If you do all of what I say, it's a reasonably safe and healthy pastime.

> If the risk is 100x

Where does this number come from?

People who bike for transportation, not just fun, sometimes need to bike at night, on less bike-friendly roads, or without high-visibility clothing. It doesn’t seem to me that the sentence for that should be death.
> or without high-visibility clothing.

Please, try to get some high-visibility clothing. The difference in visibility is between hundreds of meters with high-visibility clothing and meters without.

> It doesn’t seem to me that the sentence for that should be death.

Maybe not death but severe injuries. Being visiblevin the night is a game changer.

At the very least wrap your bike frame in reflective tape ("DOT C2 tape" is what you want to punch into Amazon if you're in the US).
Not really an option for people who mainly ride bikeshare bikes (e.g. me). But those have pretty good lights, at least.
Why don't you paint your car fluo yellow and put a big fluffy bumper around it?

Since it's your car that does the killing in an accident, not the cyclist. Right?

"You" is singular as a cyclist. Wearing appropriate gear can drastically improve your (again, singular) safety.

"You" is plural for motorists. A single motorist deciding to own and operate a soft-and-safe-mobile will not affect your (singular or plural are interchangeable here) risk appreciably.

It doesn't mean you're wrong, and you (singular) can pick your battles, but I think I'd prefer to be alive than correct.

With electric bikes there is the possibility of adding safety gear to bicycles since the extra drag can be offset by motor power. Even just the simple example of allowing the rider to wear better, motorcycle-style protective gear would be a massive improvement - since they aren't pedalling so hard. Such gear could be actively heated/cooled as well.
I'd rather be in a small car and hit a tree/electrical pole than in a massive vehicle.
Since the heavier vehicle has higher momentum, it would decelerate slower when hitting a semi-static-object, which decreases the forces on your body. The smaller vehicle would stop much quicker and you would jerk forward. So a heavier vehicle at the same speed would probably be better, all else being equal. And that's neglecting the additional material a larger vehicle typically has that deforms over longer distance than with a shorter car.
>it would decelerate slower when hitting a semi-static-object

You just changed the problem.

Did I? Trees and electrical poles aren’t completely rigid, right?
To a car? Many trees are! They are quite rigidly affixed to the ground.
So many are and some aren't. So in many cases it doesn't matter which car you're in, and in some cases the heavy car is better. That means the heavy car is still net better.

I still haven't seen a single argument why a smaller car would be better in a collision.

Yeah, the point was deliberately to show that a small car performs better in such situations.

If you had to change the problem, it shows you were avoiding the uncomfortable truth.

But a small car doesn’t perform better, why would it? Surely a large car is better when driving into an electrical pole than a small car. What advantage does the small car have?

Also, just to clarify, how did I change the problem? The problem with car crashes is rapid deceleration which injures you, and lighter cars are worse in that aspect compared to heavier cars.

Not really, the car itself is a semi-static object, even if you're driving a block of raw steel.
I did automotive safety and I can assure you, these act as static for all intensive purposes.

Being a skeptical Socrates doesnt change that the momentum is significantly higher, and you arent moving that pole any significant distance.

I'm not sure why there is such a strong denial of reality here. Is it ego?

Crumple zones have been a thing for almost a century.

Momentum doesn't matter. It matters in a vehicle on vehicle collision, but since the pole is essentially infinite I'm not sure why you're bringing it up. Acceleration is what impacts the human body, and it's determined by speed and distance. For the same speed, a larger car will have a longer distance to stop, therefore lower acceleration, and less force on the body.

Even if you assume that the pole doesn't move at all, having less momentum doesn't help you. A smaller car isn't better, in the best case it is equal. But a larger car probably also has a larger crumple zone so it is still better. You still haven't given a single reason why a smaller car would have an advantage.
I'd rather be in a tank and flatten the tree / pole.
I`d rather there were more trees and fast, affordable public transport options.
Interesting to hear the rationale in this choice ?
Might save the tree...
Good point.