>I've always read that road damage was caused by heavy vehicles(semis) which stress fracture the roads, which in turn fill with water, freeze, expand, rinse and repeat. This article seems to imply it's caused by the road design itself, though. Wonder which is true (or both)?
In my experience, both.
Set aside for one moment this new roller, the reality is that road paving is not exact science, and - even if it was - it is largely executed badly.
Paving (and before paving the underneath layers) are more like "cooking" than everything else.
It is not like you have the right recipe, good ingredients and follow "instructions" accurately you can replicate some dishes.
Usually (of course it greatly depends in local uses and materials available) the first mistake is under-calculating the thickness and consistence of the bottom layers (gravel, sand, quarried rubble, sometimes mixed with cement or lime).
The second one (again usually, not always) is inadequate protection from running water (be it coming from rain or from the soil).
Then it comes the exact composition of the asphalt, the (right or wrong) type and quantity of bitumen, the temperature at which it is mixed, transported and layered, the amount of compacting, etc., etc.
In the last 20 years or so some great betterings have come from the use of reinforcing layers, both in the underpavement (woven or non-woven geotextiles) and in the asphalt itself (geogrids, usually plastic).
Whilst geogrids in asphalt are rather costly (both as material and additional work to lay them), high strength geotextiles are relatively cheap and it is surprising how - still today - they are not widely and universally used.
Both however are only good for highways and roads outside the city, as the benefit of these textiles is to spread as much as possible any dynamic action provoked by heavy traffic and loads onto the widest possible surface, but in urban contexts the surface (and up to 1-1.5 m depth) is "ruined" by every kind of duct, pipe, cable and other services, often re-cut (over and over) for maintenance/repair/replacement.