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You'd get at least twice the life of these expensive roads if everyone rode bikes. Think about that.
Someone posted this link below and you have the right idea (that bike = less damage = road lasts longer) but you're ever so slightly off with you 2x estimation. Just a smidge out :-D
https://en.wikipedia.org/wiki/Fourth_power_law
The road stress ratio of truck to car is 10,000 to 1.
The road stress ratio of the car to bicycle is 160,000 to 1.
To put it another way. This means that after 160,000 crossings, the bicycle causes as much damage as the car does when driving on the road only once.
A truck, ONE truck, ONE time, is this number of bike crossings (if I mathed it right??): 1,600,000,000?! What even is that number?? It's in the billions!? I mean there might not be that many bike crossings before the heat death of the universe?! And that's just ONE truck, ONCE!?
Conclusion: Roads would last till the ends of time if they were only utilised by bicycles! Even if you only built roads to last ONE year under heavy truck use, under heavy bike use this same road would last 1.6 billion years!? Is this even real?! Am I mathing wrong?!
They wouldn't last till the ends of time, but the limiting factor would be environmental weathering (frost heaving, weeds growing in cracks, etc.) rather than vehicle loads.
I know :-p Spherical cow in a vacuum :-) It highlights the difference in truck v car v bike, all else removed from the equation, and shows that bikes basically have (approaching) zero impact on roads built for cars/trucks. Another way to look at it is if you only had to engineer roads for bikes they could be a fraction of the cost AND last a lot longer! Sigh, dreams are free!