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Comment by _Microft | Hacker News Reader

Maybe offtopic but a surprising bit of extra information regarding wear and vehicles:

Road wear scales with the fourth power of axle load, so heavier vehicles do much more damage than one might expect.

Take a 40t truck with 5 axles vs. a small car with a weight of 1t and two axles (e.g. VW Polo, maybe an older VW Golf might only weigh 1t as well):

(8t axle load / 0.5t axle load) = 16^4, i.e. the truck puts 2^16 (65536) times as much wear on the street as the car.

(8t axle load / 1t axle load (SUV)) = 8^4 = 2^12, even comparing it with an SUV and an axle load of 1t each, the truck is still 4096 times worse.

https://en.wikipedia.org/wiki/Road#Maintenance

https://books.google.de/books?id=7Yqxyefv-VAC&pg=PA252&dq=4t...

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> Take a 40t truck with 5 axles vs. a small car with a weight of 1t and two axles ...

Truck driver. Not quibbling, just adding nuance.

For your typical 40t scenario, allowed max weights are:

12,00 pounds on the front steering axle. It has one tire at each end.

34,000 pounds total on the two tandem "drive" axles on the truck. There are two tires at the end of each axle, so four per axle, eight total at the drive axles, and ten total on the truck.

34,000 pounds on the two tandem axles on the trailer, two tires at the end of each axle, eight total on the trailer axles, 18 total on the truck plus trailer rig.

34K + 34K + 12K = 80,000 pounds = 40t, if the trailer is fully loaded to max. It's about 35,000 pounds total if the trailer is empty.

So you should include in your calculations that the load is spread out over eighteen tires, as above.

There is also bridge loading to consider. https://en.wikipedia.org/wiki/Federal_Bridge_Gross_Weight_Fo...

So it would be better to have a bunch of smaller trucks moving cargo. And that means a lot more work for truck drivers.

True, reducing the cargo would require more trucks to carry the same load, increasing demand for truck drivers.

On the other hand, wouldn’t reducing the amount of cargo a single truck can carry makey individual truck driver less valuable?

The end result would probably depend on a lot of other factors, including the supply and demand curves for alternative forms of transportation (trains, boats, investment in autonomous solutions), as well as the supply and demand curves of the goods being transported (because if the cost goes up to pay for more truck drivers, maybe people will just stop buying that product).

Lots of ways to cut that. Consider pounds-mile/gal for freight on my 80k truck carrying 45k freight, vs your vanagon or beemer.

My truck gets at least 6mpg, usually 7.5, sometimes 9, and I've seen 10 once.

It may be better for the roads, but it may be overall worse for the environment and/or shipping costs.

Building an entire truck isn't free from cost and environmental impact, nor is maintaining it.

Fuel usage also increases with more trucks.

There's also an overhead each truck has that scales differently from how much it lugs, based on fuel it needs to carry and space for its driver.

Or for the companies who will own/lease the automated fleets, foregoing having to pay wages, health insurance, vacation time, or work breaks allowing them to ship quicker since they aren't forced to stop driving and take a break every x hours. You'll just get a smug smile and a "learn to code" line.

No, for the roads it would be better to have the weight distributed on more "area", hence: more wheels and bigger wheels for the same weight. And this does _not_ require more trucks, just more wheels below each truck.

However, an even more material-efficient solution would be to use railways instead.

> Truck driver. Not quibbling, just adding nuance.

You're absolutely quibbling though.

> So you should include in your calculations that the load is spread out over eighteen tires, as above.

The fourth power rule is specifically about axle load, not about wheel load. It's also an estimate / rule of thumb (which is why it's so useful), not a precision instrument.

But hey if you want more precision than the FPR we can do more precision: https://pavementinteractive.org/reference-desk/design/design...

As the link notes, road engineers usually work in LEF/ESAL (ratio to a standardised 18000lbs axle load), and provides some conversion tables.

Assuming a relatively large 4000lbs sedan this is 2000 lbs per axle, or 2x0.0003 LEF = 0.0006 LEF.

A fully loaded truck would be ~0.3 for the 12000lbs front axle, and 1.11 for each of the rear tandem axles, for a total of 2.52 LEF.

2.52 / 0.0006 = 4200. Which shows that the fourth power rule's 4096 was pretty close but if anything underselling it.

Yeah, they use dual tires so that they don't pop catastrophically, not to spare the road from wear.

I'm sure that's true, but are you saying it doesn't reduce wear?

I'm sure it reduces wear on the tires.

"The AASHTO load-equivalency factors strictly apply only to axles supported at each end by dual tires. Recent increase in steering-axle loadings and more extensive use of single tires on load-bearing axles have precipitated efforts to examine the effect on pavement wear of substituting single for dual tires."

https://www.fhwa.dot.gov/reports/tswstudy/TSWwp3.pdf

It probably reduces wear slightly. Increasing contact area necessarily decreases applied pressure. Then again, a wider effective contact profile damages more of the road than a narrower one would.

Let's not forget the context of this discussion, however. Fourth power expressions are still fourth power expressions after multiplication by a constant factor. 4/18 is a constant factor.

You're multiplying the input by a constant factor. If wear is proportional to (weight per tire)^4, and you've halved weight per tire by having twice as many, you've just reduced wear to 6% of its original value.

I don't know if doubling tire counts really does this, but it's hard to see why twice as many axles would help but tires per axle would not. It's possible (the pressure underneath the tires is reduced, but the tires exerting pressure on the road are closer together) but counter intuitive to say the least.

And there's no proof in this thread that it doesn't help except for masklinn's misinterpretation of the original study.

Also, road wear is a function of friction as well as pressure. Friction is increased with additional tires.

This is already taken in to account with the forth power rule, isn't it?

Fourth :)

That's been the benefit to me, still having a drivable rig when a tire shreds.

But, there is also something called a "super single" that's a double wide single wheel/tire, with one on the end of an axle rather than two. I'm told they're cheaper and lighter total, as opposed to the more common two per end. I've pulled a few trailers that had them. I don't really know why one or the other, I just drive them.

> The fourth power rule is specifically about axle load, not about wheel load.

Misunderstood that, sorry.

No, parent is mistaken. The forth power rule bakes in an assumption of dual tires at each end of an axle.

This fact is especially pertinent when folks with their F150s demand that road bikes be taxed equally to use bike lanes.

Taxing by fourth power axel weight per mile sounds good

$10 for a bike doing 1000 miles a year, so 1 cent a mile. Gross axel weight about 100lb.

So axel weight of 1000lb would be $100 a mile.

F150 at 2500lb would be $4,000 a mile.

I suggest putting the first year on the sale price, so that $200 bike costs $210, and the $60k f150 costs $60 million.

Yep that's usually the response I give to folks in my neighborhood FB group. They are conspicuously absent to the conversation after that.

Well maybe because it's a total nonsense argument? Unless you actually want to kill all road transport and everything reliant on it, which is effectively everything, in which case I also think it's clear why you're not getting any replies.

Per my other comment [1], it’s nonsense to actually collect $4000, but it’s not nonsense to have the ratios work like that.

Such a tax would eliminate marginal uses of trucks but not eliminate trucks entirely (since it would be a higher but not ridiculous tax).

It also works as a reductio against any wear-based tax on bikes, since it would imply an absurd tax on trucks.

[1] https://news.ycombinator.com/item?id=22519021

(Edited over past hour to fix numerous typos.)

You are missing that the cost of bike lanes isn't just in constructing and maintaining them. Adding bike lanes in cities means dropping car lanes because there's not enough space. That ends up creating potentially huge opportunity costs.

I wasn’t missing that, I just wasn’t addressing it; I was just addressing how to assess maintenance taxes. If there are other costs of having the road there, like its real estate usage, I agree that’s another factor to consider.

Okay. If we're just talking maintenance taxes then I agree the idea isn't nonsense. Excuse the misunderstanding.

Bike lanes can handle more traffic per surface area than car lanes. Utilization is unfortunately low in most areas, but capacity wise it’s a clear net gain for city centers.

Oddly enough, sidewalks are the most efficient use of space, but require good public transportation and extreme density to reach that threshold.

Not quite IMO.

Anyone who has done any amount of virtual traffic engineering (aka: Factorio, City Skylines, OpenTTD) knows that intersections are where the bottlenecks are.

Its incredibly difficult to design a max-throughput intersection. Roads have a huge amount of throughput, most "traffic" just gets stuck at offramps and traffic lights.

Narrowing a road to make room for bike lanes is a lower cost than people might think. If you're all going to get stuck at the next intersection anyway, it doesn't matter if you're a 2-lane, 4-lane, or 8-lane road.

> it doesn't matter if you're a 2-lane, 4-lane, or 8-lane road

If you halve the capacity of the road, you're just going to spread the same cars (and congestion) among twice as many lights...and make traffic far worse.

Depends. My commute home from my office has a 6km of a three-lane road and then a single traffic light. The road never gets backed up more than a couple km from the traffic light, so even dropping it to a single lane wouldn't make any real difference to the throughput. The speed you drive on the three-lane road also makes no real difference to the throughput as long as you get the same amount of cars through the traffic light at each cycle.

> as long as you get the same amount of cars through the traffic light at each cycle.

Isn’t this proportional to the number of lanes in the road?

If all the lanes are used at capacity, yes. Otherwise, no.

The bit about speed prior to lights was meant to be separate from the bit about # of lanes. To clarify - I mean, e.g. that when there's 5km of free-flowing traffic before the lights, and then 1km of congestion, it doesn't matter how fast you drive for those 5km as long as it doesn't delay your passage through the lights. I could halve my speed from the speed limit for those 5km and still arrive at the congestion at the lights before it's my turn to go through them.

It’s not all about throughput. Taking away car lanes in favor of bike lanes usually takes away parking as well.

While that certainly has the desired effect of reducing car traffic to the area, it also increases the difficulty and expense of travel to the area. We’re seeing this in Oakland now, where they’re putting in bike lanes and taking away parking, while simultaneously doing nothing about the limited public transportation system.

If you want to reduce vehicle traffic without seriously impacting the shops and restaurants in the area, you have to use both knobs available to increase people’s use of public transportation: make it harder and more expensive to drive a car, while also making it easier (and, preferably, cheaper as well) to take transit. One without the other is a disaster.

I mean, or you can ride a bike in these new bike lanes in one of the flattest and temperate climates in the US?

Oakland is littered with cars along roads in every neighborhood you go on, and the police barely enforce anything resembling traffic code (due partially to complicated historical reasons). In some neighborhoods, I've seen duplexes with more land area in cars than living space (so is it a wonder that poorer people here live in their cars when it's so easy to own and park a car?)

A bike lane or two makes it cheaper for most folks (yes including the folks living in the pop-up Oakland housing shelters, they own a lot of bikes) to safely move around, and reduces traffic from our generally saturated roads. Given the limited paving budget here (and how tectonically active the hills are), it's a wonder that bike infra has taken so long.

Moreover, the heavy private vehicular traffic in the area makes it very difficult for buses to navigate their routes in a timely manner, and taking parking off the road for bike lanes and BRT is a much cheaper way of enabling transit in the area that laying down rail.

Sure, you can ride a bike. Now, tell me how you would transport groceries for a family of 4, or how you transport the kids to doctor's appointments, for instance. What about people who physically can't ride a bike? What if I'm coming from 15 miles away?

I don't think the argument was to remove all car lanes and replace them with bike lanes.

(A) Use panniers

(B) Use a trailer the kids can ride in

Surely as someone from the area you've seen the countless folks with cargo bikes transporting their kids? I live 1.5 mi. away from my grocery and I take panniers and shop for a family of 2 (though I understand that kids need a lot more things than adults do, so this isn't an apples-to-apples comparison). And if you're coming from 15 mi. away, you're a guest, not a resident, so either take transit and a bike share or circle the block for parking. I don't demand a house in your yard, and neither should you demand a parking spot in mine. Also, what about the folks that physically can't drive a car but can ride a bike, or the folks with poor reflexes or vision that should not be allowed to drive and yet are given a pass in the US because it's so driving centric?

One effect that I’ve seen pretty consistently is that adding traffic lanes to a single-lane local road almost always slows down traffic. This is because every intersection needs a stop light.

But intersections also suffer if you give them less lanes. Say for each direction you have two lanes in your intersection, one for people going straight or turning right and one for people turning left. To get bike lanes, there’s no choice but to drop the lane for left turns (and my city has done this in a few places). Now you either forbid left turns completely on that intersection or every left turning car will completely stop traffic until it can move. Either way you’re creating a total mess.

In Oslo, Norway the city builds a lot of bike lines . It narrowed streets for cars or removed parking places. I talked with a few folks with cars in the city and their typical response that it made them to get work faster with a car. Surely they have to walk more to a parking spot, but after that they drive faster through the city. Apparently street parking creates a lot of congestion.

There are opportunity costs in the other direction too.

If everyone switches to bikes, then weathering will be the primary form of road wear. It might already be so in harsh climates with freezing wet winters and hot desert summers (not sure though).

When built properly, roads are quite resistant to the elements, though the execution is often culture-dependent. Roads for light loads can be built much cheaper.

Snow plowing absolutely destroys roads. The blade catches on the smallest imperfections and creates potholes. Then water gets in and the freeze/thaw expansion cycle quickly makes things worse. Here in Canada roads really don't last very long before they have to be peeled up and put down again.

Yes, but this doesn't create particle pollution, just potholes.

Obviously you would try to saturate such tax revenues at the actual cost of road maintenance, so you wouldn’t actually collect $4000/truck mile, but yes, that’s the approximate ratio the taxes should be relative to each other.

Perhaps a inverse tax tied to economic output of that vehicle. The higher the economic contribution of the vehicle, the lower the tax. So a recreational cyclist pays more than a delivery truck because the delivery truck is contributing to the economy and not simply joyriding.

That seems too easy to game, and the system might have low compliance. Who's to say when a person is joyriding vs commuting to work on a bicycle? If we're taxing based on the economic output (which we hopefully already are via income/sales taxes), does the time value of goods being transported now get included in the calculation?

That is way too arbitrary. Just because money exchanged hands at some point doesn't mean the transportation is a net benefit or should be encouraged and everything else discouraged.

Besides, I think the economy would be much healthier if everyone was riding their bike recreationally (healthy bodies, healthy minds). And a much bigger boost to the economy than a delivery truck driving 10 miles to deliver a $2 package.

Why? If a vehicle has high economic output, presumably the owner is already getting paid for it?

Sure, but we're talking about F150 type trucks here. Most people in cities have those for completely personal reasons and not for "economic activity."

On the topic of tire wear, I find that my rear bicycle tire will last roughly 3000 miles/4800 kilometers. Even summer performance tires on cars will last about 8000 miles (and most all season tires will go for at least 20,000 miles).

I recall a buddy proselytizing on the virtues of rotating your bike tires every couple thousand miles, which for that group was about once a year (and replace in the spring)

My issue with that is how your control comes from the front tire on bicycles. Anytime I have a tire issue the front tire gets the newest rubber. Rotating tires is just spreading the wear and reduced traction to your steering tire.

What I normally do when the rear tire is worn, is get a new tire, mount it on the front and move the original front tire to the rear. Even after 3000 miles of riding, my front tire doesn't show much wear at all. The rear tire, on the other hand, will have virtually no tread left.

After thinking about it a bit, I believe he was suggesting rotating at 1k, and replacing the tires every 2k. Which would still leave an awful lot of tread, but also be a more aggressive replacement period than most people would do.

I remember a hitchhiking ride in France with a man working in the building and infrastructure industry telling me about these figures, and the intense lobbying against transporting goods on rails...

In France the rubber tyre lobby is so strong, the got them on subway cars. No joke: https://en.wikipedia.org/wiki/Rubber-tyred_metro

At Michelin, we're more than just Green guides, we put our tires on the subway cars and encourage protesters to use ours for all their tire fire needs.

Maybe the study should also take into account this use of tyres.

The subway has tires for technical reasons. Stations in the Paris subway are close enough that better acceleration times have a significant impact on travel time and peak-hour capacity.

If they were willing to retool, you’d think they’d just go with a maglev monorail design. Those have the capacity for the instantaneous acceleration of a railgun.

That would be a pretty rough ride. I wouldn't want to be a straphanger on one of those. The turns would be uncomfortable as well in a railgun railway car.

It would also be useless, the stations are so dense that you would barely increase the average speed.

I didn’t mean to suggest you’d use it as a railgun. It just has the capacity for exactly as much torque as you need from it at any given moment.

In January there was this report: Microscopic pieces of plastic have been discovered in the most remote locations, from the depths of the ocean to Arctic ice. Another place that plastic is appearing is inside our bodies. We’re breathing microplastic, eating it and drinking plastic-infused water every day.Plastic does not biodegrade. Instead, it breaks down into smaller pieces, and ultimately ends up everywhere, including in the food chain. Pieces that are less than five millimeters in length, around the size of a sesame seed, are called “microplastics.” https://graphics.reuters.com/ENVIRONMENT-PLASTIC/0100B4TF2MQ...

On Germany the best lobby work to put transportation on truck instead of rail is done by DB, German Railroads, with their freight services. Compared to trucking you can easily double lead times, increase costs per ton and decrease trackability and reliability.

Same thing in Sweden.

Lower costs for the customers and higher reliability when you ship by truck means rail is not really a consideration even though it would be better for everyone if it actually worked.

A family member was a civil engineer in the Federal Highway Administration for many decades, specifically in concrete pavement design, and remained an a technical career path the whole time.

He had many war stories to tell related to the trucking industry. In one, they had developed a scale that could measure the weight per axle of vehicles on the roadway without requiring the vehicles to slow down. They wanted to embed these in a few places to prove how bad things really were with overloaded trucks.

The trucking industry bought off some congress critters who would only allow them to put the scale at one clearly marked location on an interstate, in one lane. The lane next to the scale lane was crushed by all the trucks driving in that lane to avoid the scale.

I remember a civil engineer telling me once that if highways only had cars on them they would last 100 years between repavings.

I highly doubt this in cold areas but might be true elsewhere

Plow trucks aren't cars.

Pretty sure GP is referring to the damage caused by the freeze/thaw cycle.

The problem isn’t the plow trucks, but the expanding and contracting water causes cracks. Roads that never get trucks on them get potholes

My dads driveway in upstate NY was paved in the 90s and is pretty pristine, but it’s surfaced every 2 years and well drained.

I don't doubt it, we have a local road here that has been fine, but this year they decided to drive a lot of truck loads of snow to save a skiing event from another city up that road and now it's completely destroyed and it needs new pavement and possibly new foundations in several places.

Trucks should really only be a last resort for the last mile to the store and the rest should be sent by rail or boat and loaded onto trucks if necessary.

They also have huge externalities when it comes to damage to other cars, when my car is hit by rocks on the road it is always coming from a truck.

We have such roads here in NY called parkways, cars only no busses or trucks. Absolute disasters. I frequently take the Belt parkway in NYC to long island via the southern state parkway. That thing looks like it was carpet bombed. They have been patching massive delaminations and joint failures on a weekly basis all winter and we have barely had any freezing weather or snow (it's been spring all winter.) One delam by an interchange was so deep that it took out a few car tires with low side walls.

I was annoyed at these failures and some light reading. You can make more robust roads by making them thicker with a sturdy foundation. Of course this comes at a much higher cost. For example, the autobahn pavement thickness is 27 inches. Whereas by me they mill a few inches off the top of whatever sad situation in below and top it with another 4 inches or so. This is because robust roads are costly and there are so many other things in a muni budget which need attention. So they compromise and lay down a cheap road.

I drive on one of the routes used by lorries servicing the UK's largest container port. The roads are visibly buckled in the lanes the lorries use. You can feel your car uncomfortably slotting into the grooves. It seems insane to me to use the roads for that. A railway seems like a complete no brainer, especially considering these are containers and easily loaded.

But at least the weight of a lorry consists of mostly the goods being transported. The more pertinent comparison is a bicycle vs single-occupant "SUV". Unlike lorries, those things are tearing up smaller roads in town centres making the roads barely usable by smaller cars, let alone bicycles, despite the fact that cyclists contribute equally to road maintenance.

Those SUVs also require larger brakes which is a major non-exhaust emission. It's high time to start taxing these vehicles heavily and I think using the fourth power of axle load seems like a sensible way to do it.

Like hiking trails. It takes a large number of people on boots to do the damage of one person on a horse on horseshoes.

I'd be interested to know how wear scales with tyre pressure.

The tyre pressure exactly matches the pressure on one spot on the road surface, so if pressure is higher, a smaller area of the road receives more downward force, causing it to bend and flex, and eventually break up.

> I'd be interested to know how wear scales with tyre pressure.

Apparently not in any way relevance in face of the fourth power rule, as road authorities worldwide just use the 4th power rule for road wear estimates, without accounting for minor factors (type of axles, axle arrangement, surface contact and suspension systems).

Do you think that has any bearing on the triple trailer situation that seems to be developing?

Depends how the axle load changes.

>Road wear scales with the fourth power of axle load

Could you explain why? (I can't view the Google books link.)

There's no "why", it's a rule of thumb / estimate called the "fourth power rule" (or "fourth power law" but there are other unrelated fourth power laws) established experimentally in the late 50s / early 60s by the AASHO. Basically they built a bunch of roads to the same specifications, drove streams of vehicles through and monitored pavement deterioration.

I'll take your off-topic a step further ;) A couple days ago on one of the NPR shows they interviewed a long-haul truck driver. At one point he said (paraphrasing), "If you bought physical goods, it was transported by truck."

Given the amount of consumption (of physical goods) that's a significant amount of tire wear.

He was underselling it.

Unless you walked naked out into the woods and built your life entirely from found materials, literally everything in your life was at some point or another hauled by a truck.

Everything.

This is not a hyperbolic way to make an argument, it's the truth. Sometimes you'll have to go pretty far back the chain of events, maybe as far as raw materials, but at some point (probably several) X was on a truck for any X.

A hippie commune that grow all their own food living off the grid? Their clothes, their tools, the paint on their house, it all rode on trucks.

Two-ish years ago truckers in Brazil went on a strike to protest increased gas prices and corruption and it only took three days before the president ordered the military to force the trucks into moving again. That's how hard it hits if trucks stop moving.

The military couldn't do shit though because the trucks hauling the diesel powering the military vehicles were part of the protest so they got nowhere.

If all the trucks stop right this second, we'll be living in post-apocalyptic chaos by Friday. No joke.

Suggests we should ban buses.

> Road wear scales with the fourth power of axle load, so heavier vehicles do much more damage than one might expect.

Yes. Electric vehicles with their heavy batteries also make things worse.

Not really. EVs are slightly heavy. Loaded trucks are much heavier.

Except no. The heaviest Tesla Model 3 weighs 4,100 lbs. The heaviest Ford F-150 (the most popular vehicle in the US) weighs 5,600 lbs.

Right but people buying F-150s are not buying Teslas. The use case is quite different. My Subaru Outback (a rather large car in comparison to the Tesla) is 3,600 lbs. But I doubt the increase in weight is a huge factor in environmental concerns.

But compared to freight trucks, the F-150, the EV, and the Outback are all inconsequential.

> The use case is quite different.

If you want to make this argument you should account for the weight of a loaded F150

> Right but people buying F-150s are not buying Teslas. The use case is quite different.

Have you been to a Texas city? They're full of F-150s driving around a single person and an empty bed on paved roads.

Sure, farmers and contractors use trucks as trucks, but thousands of people use them as commuter cars. Most pickup trucks are used as trucks once in a blue moon.

A Toyota Camry weights 3600lbs, so it's not like EVs are extraordinary heavy either. Additionally, 15 gallons of gas is about 100lbs.

Isn’t Model S closer in size to Camry? A Corolla is closer to model 3 size and more like 2900lbs. The P90D with less range than that 100lbs of gas Camry is 5000lbs.

Interior dimensions are all very similar. Exterior, the Model S is the largest, followed by the Camry, Model 3 then distantly the Corolla.

            Shldr  Hip   Head  Leg
  Model S:  57.7   55.0  38.8  42.7
  Camry:    57.7   55.4  37.5  42.1
  Model 3:  56.3   53.4  40.3  42.7
  Corolla:  54.0   53.9  38.0  42.0

            WB     Len    Wdth  Hght
  Model S:  116.5  196.0  77.3  56.5
  Camry:    111.2  192.7  72.4  56.9
  Model 3:  113.2  184.8  72.8  56.8
  Corolla:  106.3  182.5  70.1  56.5

Interior volume of Camry is 115 cu ft (27lbs per interior cubic foot without gas, some marginal amount more with the same amount of gas as P90D's range, which only takes around 60-80lbs of gas or so).

Model S P90D is 120 cu ft (41lbs per interior cubic foot).

Does that take into account cargo space?

15 gallons of gas is 90 pounds.

You are comparing an F150 with a Tesla 3?

Side point: EVs do most of their breaking via regeneration, so much less brake dust emission.

The battery is heavy but the powertrain is much lighter. You can make light electric vehicles, look at the i3 for example.

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