this post was submitted on 05 Apr 2026
260 points (97.4% liked)
Fuck Cars
15441 readers
808 users here now
A place to discuss problems of car centric infrastructure or how it hurts us all. Let's explore the bad world of Cars!
Rules
1. Be Civil
You may not agree on ideas, but please do not be needlessly rude or insulting to other people in this community.
2. No hate speech
Don't discriminate or disparage people on the basis of sex, gender, race, ethnicity, nationality, religion, or sexuality.
3. Don't harass people
Don't follow people you disagree with into multiple threads or into PMs to insult, disparage, or otherwise attack them. And certainly don't doxx any non-public figures.
4. Stay on topic
This community is about cars, their externalities in society, car-dependency, and solutions to these.
5. No reposts
Do not repost content that has already been posted in this community.
Moderator discretion will be used to judge reports with regard to the above rules.
Posting Guidelines
In the absence of a flair system on lemmy yet, let’s try to make it easier to scan through posts by type in here by using tags:
- [meta] for discussions/suggestions about this community itself
- [article] for news articles
- [blog] for any blog-style content
- [video] for video resources
- [academic] for academic studies and sources
- [discussion] for text post questions, rants, and/or discussions
- [meme] for memes
- [image] for any non-meme images
- [misc] for anything that doesn’t fall cleanly into any of the other categories
Recommended communities:
founded 2 years ago
MODERATORS
you are viewing a single comment's thread
view the rest of the comments
view the rest of the comments
You are thinking of perfectly elastic collisions. That's a fantasy and not applicable to the real world. A human body isn't a beach ball and cars have crumple zones (although I believe pickups suck in this regard as well).
And your comparison isn't applicable in terms of masses either. Both a sedan and a pickup are way heavier than a person.
Edit: Without getting too deep into the math, let me put it this way: The energy of the impact is equal to the energy that the car loses during that impact. The car doesn't lose mass, so it depends instead on how much the car loses velocity. That depends on how the mass of the other object stacks up against the mass of the vehicle. Car hits something much heavier than itself? It stops and all of it's kinetic energy is expended. Car hits something much lighter? A bug on a windshield. A human obviously isn't quite as neglibly light as a bug and the mass of both the human and the vehicle do factor into this, but with both a sedan and a pickup truck, the speeding vehicle never expends more than a fraction of it's kinetic energy on the impact itself. The rest of it is dealt with via breaking, and a pickup will have a harder time slowing down due to it's kinetic energy.
Car crumple zones are tuned to prevent damage to the car, not to pedestrians. If they were they would have airbags on the front of the car. A car can kill a pedestrian by hitting them with a crumple zone, without that zone crumpling.
This means most of the non-elasticity is in the pedestrian's body; how they flop onto the hood of a normal car, and how their bones crumple and flesh splatters before their brain and vital organs do.
Of course if a car hits a pedestrian hard enough, the crumple zone will crumple to reduce damage to the car, but that's overkill as far as the pedestrian's life is concerned.
That said, if you (unrealistically) assume the speed at impact and the geometry of the hood are the same, the difference between a car that weighs 20 times what a person does and one that weighs 40 times that is (40/41 - 20/21), or only about 2.5%.
Realistically, the weight increases the braking distance and the hood geometry makes the pedestrian's body perish more elastically.
Well, yeah. I can kick a dent into a car, but mostly I just raised crumple zones to emphasize that these are inelastic collisions we're talking about.
And yes, the breaking distance is pretty much the only way that vehicle mass is relevant for pedestrian survival.