I'm not sure if you've lived in low-density rural areas that are dependent on many roads, but when you do you see traffic isn't always the dominant factor. In many rural & suburban parts of the US road maintenance is heavily driven by the freeze-thaw cycle's damage - back roads will simply crack, buckle, and come apart. Living in both rural, lower density parts of New England and the even sparser US Rockies you see this continuously. A road with literally no traffic will still start to fail over just a few years. Similarly in wet soils & heavy root areas I've lived in rural roads also accumulate a lot of non-traffic damage even when you don't get sinkholes. Bridges wash out, culverts get blocked, nothing lasts. Even desert areas can have issues with drifting sand and the occasional serious cracking.

Basically dealing with infrastructure in rural areas you can't pretend that the earth is stable & inactive and no rural place can afford the most durable materials.

> I'm not sure if you've lived in low-density rural areas that are dependent on many roads, but when you do you see traffic isn't always the dominant factor.

I've worked in low density rural areas, though I've only lived in urban and low-density suburban areas, mostly the latter.

And, yes, if you have very little traffic and very little of that is heavy vehicle traffic, weathering becomes the dominant factor.

If you have signficant traffic, it becomes the dominant wear factor, even though you still have the full impact of weathering. High population density doesn't eliminate the freeze/thaw cycle.

> Basically dealing with infrastructure in rural areas you can't pretend that the earth is stable & inactive and no rural place can afford the most durable materials.

You can't pretend that in urban areas, either, which (among other factors) tend to be next to major waterways which have substantial impacts on stability.

> and no rural place can afford the most durable materials.

What you mean is “no rural place finds it cost effective to pay for the most expensive materials that are needed for heavily trafficked urban roads, because the maintenance cost with cheaper materials to keep roads in conditions suitable for the actual demands placed on them in those areas is lower than if the more expensive materials were used.”

Which gets back to my point that, sure, low-density areas have more linear distance of road per person, but also lower build and maintenance costs per unit of linear distance of road.