this post was submitted on 10 Dec 2024

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185

Vehicle height compounds dangers of speed for pedestrians (www.iihs.org)

submitted 2 weeks ago by Joker@sh.itjust.works to c/fuckcars@lemmy.world

20 comments fedilink hide all child comments

IIHS researchers analyzed pedestrian crashes to develop injury risk curves showing how speed affects crash outcomes. They found that the effect of crash speed on injury risk was magnified for vehicles with taller front ends. Compared with risk curves developed using crash data from Europe, where tall passenger vehicles are less common, risk curves for the U.S. show pedestrians here begin to suffer more serious injuries at lower speeds.

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[–] donuts@lemmy.world 38 points 2 weeks ago (1 children)

Before anyone is like "of course, we already knew this"

Now it's proven with empirical data. This is what matters.

[–] FireRetardant@lemmy.world 14 points 2 weeks ago* (last edited 2 weeks ago) (1 children)

The issue isn't data, the issue is breaking the car culture. I've seen people nearly hit a pedestrian with right of way at a crosswalk while their car was turning right on red. Most of the time they freak out along the lines of "get out of the road, this is for cars." We've adopted a terrible attitude of the car driver is always right and the pedestrian is always wrong and that is the biggest thing that needs to change. We constantly accept dangerous designs that take pedestrians, drivers, and cyclists lives to save people literally SECONDS on their daily commute and whenever someone is hurt we blame the human factors instead of the designs of roads and cars.

We can throw as much data as we want, unfortunately it seems most drivers are on the side that seconds are more valuable than life.

[–] donuts@lemmy.world 5 points 2 weeks ago (1 children)

I'd argue that in order to (help) break this insane car culture, you need empirical data to prove it. This to counter the "it's not really proven, there's no evidence, just feelings" crowd.

[–] FireRetardant@lemmy.world 2 points 2 weeks ago* (last edited 2 weeks ago) (1 children)

We have the data. In my area an ancient subway moves more people than the widest highway in north america. They fight tooth and nail to prevent any new rail projects and literally have to print new laws to keep building highways that only make congestion worse. In my opinion it is way more of a culuture war than a numbers war. Many places, and even people, in north america will treat you as a second class citizen if you take transit but we bend over backwards to shave seconds off of car travel.

[–] Nouveau_Burnswick@lemmy.world 1 points 2 weeks ago

Hello Torontonian. Fuck bills 212 and 197, eh?

Kingstonian.

[–] Kolanaki@yiffit.net 12 points 2 weeks ago

I definitely should not be able to see a Ford pickup truck's bumper at the same level as my Fiesta's god damn windshield.

[–] Pyr_Pressure@lemmy.ca 1 points 2 weeks ago (1 children)

Is it the height that's an issue or the weight of the vehicle? I imagine taller vehicles are generally also a lot heavier.

Or is it because it becomes a wall hitting a pedestrian instead of something you can roll over the top of?

[–] Walk_blesseD@lemmy.blahaj.zone 1 points 2 weeks ago

Both!

[+] chillinit@lemmynsfw.com -18 points 2 weeks ago* (last edited 2 weeks ago) (3 children)

Injury is caused in the inelasticity of the collision, the energy absorbed by the body. To compute that we need to know both the vehicle's speed and it's mass. However, this study ignored mass. The best it can do is find a correlation. Very little of the article's conclusions in causation or implied remedies have much merit.

A high school physics student should be able to explain this in terms of momentum, energy, and scientific method. An AP student can also do the math. By second year of post-secondary they can communicate it to another. The actual scientific paper wouldn't dare present in such a ridiculous manner as this article.

[–] vin@lemmynsfw.com 10 points 2 weeks ago (1 children)

It's relative mass that matters. Weight of a car to the weight of a person is so high that a vehicle being 5 times heavier than another vehicle is irrelevant.

[+] chillinit@lemmynsfw.com -14 points 2 weeks ago (1 children)

Weight of a car to the weight of a person is so high that a vehicle being 5 times heavier than another vehicle is irrelevant.

Like I said above, a high school physics student knows better than this.

Show us your math so we can laugh at you.

[–] Albbi@lemmy.ca 6 points 2 weeks ago (1 children)

You sound like someone who has learned to critique scientific papers, but hasn't learned enough about how to actually improve on their methods. You sound like an absolute dick.

The paper shows vehicle height contributing to more serious outcomes. You could infer that the weight of the vehicle is correlates with vehicle height and therefore the mass of the collision is incorporated in the data. Vehicle height has the added benefit of also incorporating collision strength as pedestrians can't fall on the hood of the car and have that absorb some of the impact. There are huge vehicles that will probably hit me right in the head on a collision which would further contribute to the severity of the impact.

[–] yimby@lemmy.ca 9 points 2 weeks ago* (last edited 2 weeks ago) (1 children)

At the risk of feeding the troll, here is the math you are suggesting we do, which disproves all of your arguments. It pains me how confidently you speak of a topic you are clearly so uneducated about: your physics mentors should be disappointed in you.

Conservation of linear momentum:

m~1~v~1i~ + m~2~v~2i~ = m~1~v~1f~ + m~2~v~2f~

Let the vehicle be m~1~ and the human m~2~. Let the human's initial velocity be zero. Let us further assume an inelastic collision: the human and vehicle end up at the same final speed v~1f~=v~2f~=v~f~.

Thus:

m~1~v~1i~ = (m~1~+m~2~)v~f~

What we are concerned of is the ratio of initial vehicle speed, v~1i~, to post-collision speed v~f~. Your argument is that a lighter vehicle will have a larger drop-off in speed, recovering energy and reducing the severity of the collision. If you were right, the ratio v~1i~/v~f~ should be less than 1.0, and be significantly different for a heavy and light vehicle. We will prove this wrong shortly.

Rearranging:

v~1i~/v~f~ = m~1~/(m~1~+m~2~)

Already it is abundantly clear that when m~1~ >> m~2~, v~1i~/v~f~ will be 100%. I will leave you no room for counterargument here by working two examples. Take the most popular pickup truck, the Ford F150, at 2125 kg. Take one of the smallest compact cars, a Honda Fit, at 1130 kg. Take the average adult human, at 65 kg.

For the F150: v~1i~/v~f~ = 2125/(2125+65) = 97%

For the Honda fit: v~1i~/v~f~ = 1130/(1130+65) = 95%

At 35 mph, that's a difference in speed delta of 0.7 mph, which is absolutely insufficient to explain the delta in injury severity presented in this article.

This proves what everyone knew all along: vehicle mass is insignificant in crash severity with a pedestrian because the masses of the two objects are so different. When the masses are similar (e.g. a small car colliding with a big car) yes, mass is important. But that's not what is being discussed and is not your argument.

I hope you go back to school and learn the basics before confidently acting superior. Take your downvotes and learn from this to do better.

[–] chillinit@lemmynsfw.com -4 points 2 weeks ago

Your argument is that a lighter vehicle will have a larger drop-off in speed,

This is where you went wrong.

But, you're not asking questions. So, I'll not invest into answers.

[–] Grass@sh.itjust.works 6 points 2 weeks ago (1 children)

A vehicle with a higher front end is going to be a bigger one with more mass so the results will probably be not to far off from if they actually used mass, but yeah kinda dumb. Maybe they were trying to find alternate wording because the average bigg truxx appreciator won't know what mass means.