[Retric]

Roads still need maintenance even if nobody uses them, so a significant portion is split evenly across all traffic.

Busses are light compared to 18 wheelers and other heavy equipment, they also replace many cars and SUV’s which keep getting heavier.

Finally that rule of thumb isn’t really that accurate, “A 1988 report by the Australian Road Research Board stated that the rule is a good approximation for rutting damage, but an exponent of 2 (rather than 4) is more appropriate to estimate fatigue cracking.” Rutting really isn’t that significant in most cases, but can instantly destroy road surfaces when fully loaded construction vehicles etc drive over something once.

[coryrc]

> Roads still need maintenance even if nobody uses them, so a significant portion is split evenly across all traffic.

Your former doesn't imply the latter. Here in Seattle we even still have cobblestone roads without heavy traffic and they spend very little money on them.

We have extensive rutting damage on the lanes use by busses and requires more expensive, deeper road base when they get replaced. This cost is due to the heavy traffic.

Even if squared, the buses are still 22 tons instead of 2-3 tons. 49 times more damage isn't good.

[Retric]

22 tons are huge busses and overkill unless you actually need that much space, and tend to have 4 axles. ((22 / 4)/(3/2)) ~= 13.5x a heavy SUV but could be replacing 30+ vehicles.

Also that visible ware is noticeable because it hasn’t been replaced. Looking worse when you resurface on the same schedule isn’t an actual cost.

[coryrc]

But those are what we have and they have 3 axles, not 4.

We also have many concrete roads and closely-spaced axles, if they had them, would not help.

> Looking worse when you resurface on the same schedule isn’t an actual cost.

I addressed this: they have to dig much deeper and replace with much thicker road. Much more expensive. It's not "looking worse", it's actively dangerous to cyclists and other road users, so the surface must be replaced more often too.

[Retric]

Closely space axels work fine for road surfaces they don’t help on bridges but that’s a separate concern. You can see a plethora of heavy military vehicles etc which use extra axles to avoid getting stuck in the mud due to plastic deformation IE rutting. EX: The 22 ton KTO drives has to deal with rutting on vastly worse road surfaces like mud. https://en.wikipedia.org/wiki/KTO_Rosomak

But this is where you need to do a deeper analysis than just a simple rule of thumb. Even adding extra wheels to the same axle makes a big difference to road surfaces.

> so the surface must be replaced more often too.

Level of ruts you see are considered acceptable or they would be replaced.

However, ultimately the same entity is paying for the busses and road maintenance. If lighter busses saved taxpayers money that’s what they would use which is a major sign your analysis is inherently flawed.

[coryrc]

> Level of ruts you see are considered acceptable or they would be replaced.

I guess you don't know how the USA works, and Seattle in particular. We are spending a fraction of what is necessary to keep infrastructure from failing. We had a major bridge nearly collapse and was out of commission for years. https://www.king5.com/article/news/local/seattle/seattle-dep...

Many of our roads are not what we call acceptable.

> However, ultimately the same entity is paying for the busses and road maintenance.

Hahaha nope. We have so many different organizations with their own funding sources. Roads come from State and local funds. Metro is primarily funded with dedicated sales tax.

> If lighter busses saved taxpayers money that’s what they would use which is a major sign your analysis is inherently flawed.

Sorry, but this is possibly the most naive thing I've ever heard.

[Retric]

> We are spending a fraction of what is necessary to keep infrastructure from failing.

I can’t help but chuckle at the idea you actually believe that. Stop reading headlines and do some actual research into what’s actually going on.

If the US was utterly failing in maintenance you’d see ~6,000 random bridge failures per year based on the number of bridges in existence instead they are incredibly rare showing that we are actually doing a great job overall.

[philwelch]

> Busses are light compared to 18 wheelers and other heavy equipment, they also replace many cars and SUV’s which keep getting heavier.

They don’t replace nearly enough cars and SUV’s to make up for the difference in fourth power of axle weight. But yes, 18 wheelers are worse.

[xnyan]

>They don’t replace nearly enough cars and SUV’s to make up for the difference in fourth power of axle weight

A modest bus holds 40-50 people. Most commuter traffic is single driver, single vehicle. I don't know to which power the difference in axle weight would have to be to surpass the efficiency gains of replacing 40 to 50 American sized SUVs with a city bus, but I suspect it's more than four.

[XCabbage]

At the heavy end, SUVs weigh about 3 tonnes, while at the light end buses weigh about 12, a 4x difference. 4^4 = 256. So if the claim about the fourth power is true, you'd need to replace 256 SUVs to break even on wear, which is obviously impossible.

(I don't really understand how the fourth power of axel weight thing can possibly be true, though. Why would joining two vehicles together into a mega vehicle with double the weight and double the wheel count suddenly cause the combined vehicle to inflict 16x more wear than before you joined the two together? It makes no sense.)

[philwelch]

Another example I worked out once

A Ford F-150 weighs about 2 tons and has two axles, for an axle weight of 1 ton. 1^4=1.

A garbage truck weighs maybe 30 tons and has three axles, for an axle weight of 10 tons. 10^4=10,000.

So if you drive an F-150, you’re doing as much road damage driving down the street 10,000 times as the garbage truck does once. Rural areas that don’t have garbage trucks and just expect everyone to haul their garbage to the dump in the back of their pickups are onto something.

[rkangel]

Joining two vehicles together with double the weight and double the axle count does not change the load on each axle.

So, scenario A:

    4 ton vehicle, 2 axles
    load per axle is 2 tonnes.
    2^4 is 16
    2 axles - so load is 32.
    Another vehicle the same - also loading 32
    Total: 64

Scenario B:

    8 ton vehicle, 4 axles
    load per axle is 2 tonnes
    2^4 is 16
    4 axles - load load is 64
    Total: 64

[XCabbage]

Ah, right, sorry, I misunderstood the definition of "axle weight" I got when I hurriedly googled it even though the name should've made the meaning obvious.

[ninalanyon]

The classic British Routemaster double decker weighs 7.5 tonne and can be configured with 72 seats. Newer double deckers weigh 12.5 tonne and have a capacity of 60 seated and 20 standing.

Doubling the weight and doubling the wheel count leaves the axle weight unchanged.

[adwf]

Plus the SUV is usually point-to-point, leave home, go to work, come back. Whereas the bus is going back and forth ten times per day.

In Europe, the numbers differ even more. Lighter weight cars typically 1.5-2 tons, a new London bus can be upto 18 tons when loaded - that's ~5-16 units of wear for the car to 104,976 units for the bus...

But this is all supposing we're optimising for road wear, which isn't really the point of a bus system.

[snk]

I'm old. Back in the olden days - the 1900s - 2-ton cars were not lightweight, the so-called heavy Chevys.