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Comment by nickff | Hacker News Reader

Here is the Yale press release: https://news.yale.edu/2020/09/02/asphalt-adds-air-pollution-...

And the paper: https://advances.sciencemag.org/content/6/36/eabb9785

I'd also like to point out that road wear is approximately proportional to the cube (^3) of the weight per axle on a vehicle, so cars are probably responsible for a minority of this pollution.

*edit: some are pointing out that the relevant road wear is proportional to the 4th power of vehicle weight, see the comments below for details.

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I thought it was roughly to the 4th power of the vehicle? At least that's what this chart [1] suggests and I've heard in a few engineering podcasts

[1] https://streets.mn/2016/07/07/chart-of-the-day-vehicle-weigh...

It's a complicated function that behaves like different powers at different depths.

But superficial wear (this study) should have a higher power than deep wear (your link). Civil engineers normally used the 3rd power for deep wear...

Maybe the people on your link got a table from something different than what they though it was.

Vehicle weight is not directly proportional to axle count - a 9 axle semi with trailer can weigh 80,000 lbs or 9000 lbs/axle, a 2-axle car weighs 3500 or 1750 lbs/axle. Alternatively, multiplying axle count by 4.5 increases vehicle weight by 25x - so the two can both be true at the same time, the power just changes whether you use vehicle weight or axle load.

What effect does tire width have? Very narrow (<165mm) tires vs dual tires of trucks for example. Smaller area of friction versus lower pressure

>What effect does tire width have?

probably quite an effect, but reducing damage via width will also decrease vehicle efficiency and increase rolling resistance, so the gains at the road may be lost in an overall loss of efficiency at the vehicle, not to mention manufacturing and materials cost, when finagling the tire-width variable.

I don't have any numbers, though.

> will also decrease vehicle efficiency and increase rolling resistance

Not necessarily; one could formulate the tread rubber for such wider tires so they're less grippy per square cm of tread contact-surface, and so exactly as grippy as before per fully-loaded tire. Basically making every change in the opposite direction from what dragster tires do (other than the width.)

That's for peak power. Efficiency is lost in the deformation bending and returning of the walls of each tire as it rolls. i.e. A really highly loaded tire needs to be really well pressurized to prevent overheating and failure due to the losses.

Got a link to engineering podcasts?

> I'd also like to point out that road wear is approximately proportional to the cube (^3) of the weight per axle on a vehicle, so cars are probably responsible for a minority of this pollution.

Could you clarify that a bit? Do you mean that the friction of the tires on the road releases nasty emissions?

No, heavy trucks wear out the road significantly more than cars and result in asphalt having to be replaced more frequently.

This is another case where the gas tax isn't really adequate for funding road issues due to the disproportional increase in costs to the increase in fuel usage by trucks. All of the light vehicle drivers subsidize the heavy trucks in all mileage/fuel based tax schemes.

For this reason, in northern latitudes, weight limits for trucks drop significantly during the spring season. Shipping water bottles, ice salt and windshield washer in stores becomes a real pain in the ass.

For what it’s worth, you can buy windshield washer concentrate online. In months where the temperature gets cold, though, you want the alcohol based stuff that won’t freeze and burst a line.

Sounds like we need to expand our rail capacity. Our current rail freight capacity is near 100%.

Why not tax each mode of transportation proportionately to their true cost, and let the market decide?

How do you price in the fact that heavy trucks destroy the road faster, causing them to be replaced more often, causing more pollution?

In other words, how do you price in the pollution? And do you really want to?

Yes, you really do want to. It would be lovely if we could charge proportional to the externalities.

As for how... beats me. Best we can do is rough approximation, and accept that we will continually find out we were wrong and have to adjust the cost structure.

We could get the approximations quite wrong and still get massive economic improvements from where we currently are!

However the challenge isn't the approximations, but the political difficulties. Even taxing based on mileage would cause an uproar. And taxing large pickups proportional to their economic toll on infrastructure would probably start a violent revolution.

Large pickups aren’t an appreciable part of the problem here - 18 wheelers are.

There are a lot of smaller roads where 18 wheelers never travel, and where a 2x weight increase means 10x the road wear (between the cube and fourth power of weight, according to simple models in this thread).

Charge the asphalt companies a carbon tax, and let municipalities create road taxes based on vehicle weight/usage to pay for the extra costs created for road maintenance

The how is difficult -- studies like this are part. "Do you really want to?" is a clear yes. It's called a Pigovian tax, and it's the most unambiguously "correct" way to tax things: you tax things in accordance to their harm to third-parties (and subsidize things in accordance to their benefits to third-parties).

Markets only work if we internalize the externalities, which can most efficiently be done through taxation. Pollution is one of the standard examples of an externality.

Because there is no "true cost" and it's all subjective.

You can ratchet up the tax on heavy trucks because "muh road wear" but then you'll have a world where everything is delivered in small trucks and there will be problems with that. At the end of the day it comes down to a subjective question of which problems get which priority.

or transportation of goods like food become more expensive so people rely on their local farmers instead of getting avacados shipped in from the moon

If you do anything to a low level of the economy (e.g. fuel or energy prices) to the point where consumption at the upper levels is reduced then you're also screwing the poors hard enough that you are either going to get voted out of office or shot in short order (depending on how your system of government handles power transitions).

I agree, but none of this is remotely just or fair without a minimum wage that is a living wage. And what that is needs to be reassessed if policies change the cost of living.

that's life - frank sinatra

Good thing it's something totally within our power to change. - Probably Also Frank Sinatra

>You can ratchet up the tax on heavy trucks because "muh road wear" but then you'll have a world where everything is delivered in small trucks and there will be problems with that

Is that really a bad thing? If shipping via big trucks (compared to small trucks) causes $200 more road wear per year, but saves $100/yr in gas (and other expenses), why shouldn't we use small trucks?

> At the end of the day it comes down to a subjective question of which problems get which priority.

You're right, there will be some subjectivity involved, but at least the general goal is trying to be as neutral as possible. It's not unlike cap & trade for dealing with climate change - letting the market decide what's the most cost effective way.

Small trucks may cut enough emissions by reducing road-wear. If everyone switched from large trucks to an even larger amount of small trucks it's possible the problem is made worse.

Why the focus on small trucks as if they're a panacea?

>If everyone switched from large trucks to an even larger amount of small trucks it's possible the problem is made worse.

Right, but isn't the whole premise that the damage is the truck's weight cubed (or ^4)? Splitting large trucks to small trucks only increase wear linearly.

>Why the focus on small trucks as if they're a panacea?

I'm not. It's a hypothetical.

>it's all subjective.

Let's dream for a moment where the tort system worked perfectly. All environmental externalities would be perfectly priced by class actions. Cause $100,000 of lung damage, pay $100,000 to the survivors. If only such efficient courts existed...

> then you'll have a world where everything is delivered in small trucks and there will be problems with that

So then tax those problems until taxes represent the true societal cost of things

Rail networks have massive network effects. Might be best to let the market not have that one. What with the huge risk of regulatory capture and all.

Looking at e.g. the UK, having some mixed public-private rail system doesn't seem to work that well.

The most efficient freight railways in the world are probably in the USA, and passengers in Japan. Both private vertically integrated things, with the one company owning both rails and trains. But yeah, massive potential for problems as well.

I don't really have a good solution. I'd guess the best industry structure is just "it depends", nothing that is superior to other ways of doing it in all circumstances..

I sort of wonder if private train companies in the US would achieve the sort of interconnection we have in Tokyo. The train station nearest to my house is owned by one company, but after going East two stops the stations and rails are all owned by another company. The station that's part of both of these companies' lines is also a major transfer station to a major line owned by a third company.

As a user of transit I mostly don't have to care about this, but I ended up calling three companies when I lost something on the way home.

This was sort of figured out during the massive railroad booms in the US throughout the 1800s. You can let the market have parts of it but you need guardrails so you don't have some asshole that owns a bridge holding everything up for a city: https://en.wikipedia.org/wiki/Livingston_Avenue_Bridge#Histo...

Motor carriers operate with tight margins and require a heavy regulatory hand. There are multiple overlapping jurisdictions, etc. Law of averages make fuel tax work, but there are holes... if you buy fuel in Delaware, less revenue comes to Pennsylvania, etc.

Shitty operators will do anything to save a buck -- trucks with no brakes operating overweight will travel at night to avoid enforcement based on knowledge of enforcement. Others will find holes in enforcement to avoid penalties -- shady trucks operating in Manhattan will be registered in places where unpaid New York tickets won't impact their registration, for example.

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

If you have a commercial vehicle you are supposed to be tracking how many miles you travel in each jurisdiction and how much fuel you buy in each jurisdiction.

I'm sure the "flag of convenience" states that operate cut-rate truck registrations are very diligent in auditing compliance. </s>

Don't y'all have these amazing rivers that aren't really used any more for transportation? Maybe you should couple that up with rail transport :-)

Barge traffic on rivers has been and still is a thing. Maintaining the rivers isn't cheap or easy, of course.

I know the comment was tongue in cheek, but the area in question (Los Angeles) doesn't have navigable rivers. In fact, the Los Angeles river is better paved (lined with cement for various reasons) than some roads in the area.

And as a sibling comment points out, where the US does have good rivers/lakes, notably the Mississippi-Missouri-Ohio network and the Great Lakes, they are used extensively for transport. The only one I can think of that is disused is the Hudson and canals that connect to the Great Lakes.

But the same is true for Europe: larger rivers allow larger, more efficient ships and are still used for transport, and the canal system is too narrow and so mostly recreational now.

You can always (sometimes at large cost) dig wider and deeper canals, or make existing ones wider and deeper. https://www.britannica.com/technology/canal-waterway/Major-i... has plenty of examples of recently dug or now large canals supporting large ships.

How solid is rail transportation in California?

For freight? It's pretty solid.

In calendar year 2019, the alameda corridor [1] processed about 4.8 million twenty foot equivilent units (TEU) [2] and the ports of los angeles and long beach processed about 9.3 million [3]. So around about half of the container trips to or from the port are by rail rather than truck. Some of the containers may just get put on trucks at the rail yards at the other end of the corridor to avoid trucking congestion in the port, but I don't think there's a lot of that. (I could be wrong)

For passengers? It's pretty iffy outside of commuter rail, Amtrak operates on freight lines, and is deprioritized, and there's a lot of freight volume, so there's a lot of delays for passengers.

I don't know the right keywords to find data for the ports of Oakland and Stockton. They probably have a decent rail volume too, but they have more challenging geography to get east than in southern california.

[1] the rails between the port of la/long beach and major rail yards exiting los angeles

[2] http://www.acta.org/pdf/Monthly_TEUREV_History.pdf

[3] https://kentico.portoflosangeles.org/getmedia/a43d3038-7713-...

The way you frame this makes it seem like a road tax is in our future. That, in turn, makes me more skeptical about this study, the funds for which were granted by the EPA. I’m not really insinuating the EPA is after your tax dollars, but the fact that a government agency funds a study that can have tax implications should at least raise an eyebrow. I don‘t know how common this is.

The problem I have with this is that the gas tax was [Edit: this is apparently not true, as was pointed out below] created because exhaust fumes were damaging the environment and reducing air quality - and I agree with that. But now that we have made significant strides towards reducing emissions - both in the way of more efficient vehicles and battery-operated vehicles - causing a decrease in gas tax dollars flowing in, suddenly we have another source of emissions which would require another tax.

I can’t help but feel that at least on some level this will be a money grab - even if the underlying study is confirmed long-term.

>the gas tax was created because exhaust fumes were damaging the environment and reducing air quality

Do you have a source for this? Everything I have read states that gas taxes were first enacted to finance road construction (thereby leading to more exhaust fumes), and gas taxes in place today often dedicate the majority if not all of their funds to road building.

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

Actually, I don’t have a source, it was just my assumption, so you’re probably right.

But seeing the downvotes roll in, I should have known better than to question the financial motivation for an environmental study on HN.

Pairing those questions with skepticism of government certainly didn't help.

I think the downvotes are about the misinformation, not the questioning!

I would also point out that gas taxes do not fully fund road infrastructure, and typically cover only about half the cost, meaning that road infrastructure is heavily subsidized by other taxes. (Which if course should be the case for infrastructure, but a lot of car advocates mistakenly believe that they are pulling their own weight with gas taxes.)

Thanks for the info. I’ve updated my original post to point out I was mistaken in my assumption.

As an aside, I treasure the moments when I get downvoted in HN; it's good to at least be thinking differently enough to cause a negative reaction a small amount of the time, IMHO.

You could get a decent approximation of the right tax by taxing diesel more. Especially after dieselgate, there are hardly any light vehicles that use it.

Except in Europe, where Diesel peaked at almost 50% of all vehicles sold - pre dieselgate.

That same hammer would also hamper innovation in new light diesel vehicles. All three auto makers now make diesel half ton trucks and Jeep is expanding it into more vehicles. We should encourage that.

A few things came to mind for me:

- Many of these emissions are described as being from paving, so more frequent repaving caused by increased wear would aggravate the issue.

- These issues seem to be related to temperature, and I suspect that the increased wear by heavier vehicles is largely caused by increased friction (which would increase temperature-related emissions).

- Cracks and potholes expose more asphalt, and are largely caused by the heavier vehicles.

Tires wearing out is indeed a source of pollution though. That material wears off onto the roads.

>I'd also like to point out that road wear is approximately proportional to the cube (^3) of the weight per axle on a vehicle, so cars are probably responsible for a minority of this pollution.

This is a very, very, large over-simplification and contains some large assumptions about road material, the road base, the ground pressure of the axles and the local climate (which affects the road construction techniques).

This is a rule of thumb to help city planners come up with a ballpark number that's within an order of magnitude. Don't present it as though it's a hard and fast rule.

Hence the caveat “approximately proportional”

Even if it's a ballpark figure, the GP's statement would still be correct, no?

As someone who had to study civil engineering as an undergrad a lot of the formula are empirical. 3rd power law might not coorelate with degradation of some road some road while others might exhibit 5th power law. However if I recall correctly the correlation between road wear and axle load was ^4.

Yes, each car does little damage compared to a truck or bus. But how do the numbers compare for the total number of cars vs HTV right now? Is the ratio of cars:HTV better or worse than 1:3?

Uh, why 1:3? European cars are generally about 4x lighter than European TIRs. If the proportions are similar in the US, you should be asking about 1:64 if the cube is right, or 1:256 if the fourth power is.

Edit: also, there's the duration of use per day. Typically about 1h for cars and 10h for trucks here, so you should be asking about 1:2560.

Could this problem be temporarily mediated by expanding the width of tires to increase the surface area and disperse the weight?

The press release doesn't say anything at all about road wear, pressure or friction, so cars vs. trucks has nothing to do with it.

It appears to be entirely about the role of asphalt releasing compounds when exposed to sunlight and high temperatures.

So even if there was zero traffic on the roads, asphalt would still be producing the described pollution on a bright summer day.

The greatest amount of semivolatile organic compounds escaped when the pavement was heated to 140°C

Asphalt is usually delivered at 275-300f (135-150°C) and needs to be over 185f (85°C) when applied. So, a warm summer day is cold by comparison. Resurfacing is also heavily impacted by use.

It does look like emissions are highest when the asphalt is fresh, even though they persist after that, so to the extent that more wear results in more frequent replacement (and so, more time during which the asphalt is fresh), there's probably some connection there?

Road wear is what makes communities repave roads, so cars vs. trucks has quite a bit to do with it.

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