I don't understand what you mean by your first sentence, do you mean that highways stay good because of all the fast traffic going over it?
I think it's very interesting though, that you bring into attention that roads need a lot of maintenance to stay in perfect condition for traffic like cars.
And if the roads don't get the care they need then they can get bad in only some years. Actually on wikipedia it says roads are designed in Europe to stay good for 30 years, that's quite long.
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Hi Gunnix,
Not so much the speed of the traffic but the quantity of traffic. If there is a lot of traffic on a road it tends to move debris to the verges. Little, or no slow moving traffic would not have that effect, it would just stay there, if you have a build up of debris in the road (leaves in the autumn especially) that stays there then dust etc will build up and when the seeds start to spread the following year they can become embedded in that, they send down roots that can easily get into any cracks in the surface, then water can get into the surface where the roots have grown, then in the winter the frosts get in and break down the surface even further, then the whole cycle starts again, just that the second year will be worse.
If the roads are kept clear of debris, by high volume and high speed traffic it stops this happening, and with the maintenance crews out patching, repairing, scraping and brushing the surface on a regular basis I can see that some surfaces could last longer than 30 years.
As you say, less traffic, less roads, less commuting to find work, less air travel, less heavy shipping, smaller world, more countryside for us to ride our horses or bikes in, sounds good to me...
LS