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Comment by Palomides | Hacker News Reader

the majority of the pollution probably comes from semi trucks rather than passenger cars, due to the huge weight and number of wheels

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Agree, the damage to the road (and the tyres, presumably) is proportional to weight^4.

https://en.wikipedia.org/wiki/Fourth_power_law

> The fourth power law (also known as the fourth power rule) states that the stress on the road caused by a motor vehicle increases in proportion to the fourth power of its axle load

I hate that the 4th power law is called a law. It's not a law of nature, it's a lazy curve fit.

Think about this...if car does 'x' damage to the road, 2 cars does 2x damage. 2 cars welded together side by side (axle to axle so the axle count stays the same) would also do 2x damage, but the 4th power law says it does 16x damage.

If it's wrong by a factor of 8 in the simplest thought experiment it's not a law. You can obviously make a heavy load act like many small ones, or concentrate a light load so it does a lot of damage.

Constant * X^4 just coincidentally went through the data in a single 1950s dataset...and for some reason we're calling it a law 70 years later, when it's really just a loose trend that we could easily break with a little engineering. And we probably have broken it...tires, roads, and vehicles have changed a fair bit in 7 decades.

If you're welding the two cars together connecting the axles you're still having 8 contact patches instead of 4, so the axle load is the same as 2 separate vehicles they're just moving in tandem.

You'd need to stack the two cars on top of each other to increase the axle load. In which case I'd say it's not obvious how much more the road wear would be without looking at data.

I'm not saying the 4th power law is absolute truth, I truly don't know what the wear patterns would look like on a modern surface. But your example isn't proving it wrong at all.

> Think about this...if car does 'x' damage to the road, 2 cars does 2x damage. 2 cars welded together side by side (axle to axle so the axle count stays the same) would also do 2x damage, but the 4th power law says it does 16x damage.

Are you removing the two inner wheels from the axle? Those would also support weight

A little off topic, but what are the roads releasing into the environment as they wear down? Asphalt is often somewhat radioactive since it's made from oil? Is there benzene in there? What is the scale of asphalt nanoparticles compared to tire nanoparticles?

Where i live, 80% of all vehicles are passenger vehicles. I'm not sure that the extra wheels on semis would make up for that difference, especially with the slow increase in size of passenger vehicles.

Something like 98% of ware from road vehicles is caused by semi’s vs 2% from cars and trucks.

20% * 18 = 3.6 vs 80% * 4 = 3.2, so barring some 3rd category semi’s would have more tires. They also have a lot more weight on each of those tires.

Road wear is proportional to weight.

Semi tires are hard, long-lasting compounds relative to soft consumer tires with deep treads and soft rubber.

> Road wear is proportional to weight

No, it scales at the fourth power of the axle weight.

Hard long lasting compounds don’t actually make up for fully loaded semi’s weight. They are much larger tires and with consistent heavy loads may only last 25k miles (or 100k with light loads).

So more and much larger tires and fairly similar lifespan = they liked make up a significant majority of tire pollution.

there are 200000x the number of private cars. are you sure?

Your estimate isn't even close--you're off by about 4 orders of magnitude.

Fact: In California, the number of trucks is about 300K vs cars at 14M (about 40x).

Fact: California AADT on roads for trucks ranges from a couple of percent up to almost 50%. Very few roads have less than 10% AADT from trucks.

Fact: Damage to roads goes as fourth power of axle load.

Speculation: Given that tires are the primary means to transmit that damage to the roadway, it wouldn't surprise me if the trucks are responsible for the vast majority of tire particulates.

Reference: https://dot.ca.gov/-/media/dot-media/programs/traffic-operat...

it's widely accepted that trucks cause the majority of road wear, considering the tire is the softer part in contact there, it seems pretty plausible

I don't have a citation to point to, though!

edit: there are roughly 100x registered passenger cars in the US as semis

Well, given a semi only averages 8x the miles of a car per year, your initial claim is wrong.

https://afdc.energy.gov/data/10309

Hi SideQuark. I'm writing you here as there's no contact email on your profile--I wanted to ask you if you ever tried a SAT solver on RomuTrio to find cycles (or you can give me some hints). I'm referring to this: https://news.ycombinator.com/item?id=22457101.

You can write me at sebastiano.vigna@gmail.com. Thanks for any info!

BTW, thanks for explaining that you cannot prove things about a single permutation using random permutations--it's so obvious that it is very difficult to explain, and the same absurd argument pops over and over.

Road wear depends on weight.

Semi truck tires have hard, slow-wearing compounds.

A fully loaded tractor trailer has 5 axles and weighs 80,000 lbs, it does 9000-10000x more damage than a passenger car.

This is why states operate weigh stations — overweight trucks cause significant damage.

Semi’s drive 12+ hours a day most days of the year. Passenger cars just go to work and they store and back.

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