This question already has an answer here:
Trying to get a ballpark estimate of how long it would take nature to reclaim a small (2-lane?) road/country highway to the point where it's barely discernible. Assume our species is gone - so no traffic to hasten its decay or effect repairs. What about larger highways/freeways?
Related: how long would (metal?) signs (ex. speed limit, exits) last, esp. in relation to the road. Would it be reasonable for a sign to still be standing AND legible after the aforementioned road had all but vanished? Exactly how bad off would that sign be?
If signs wouldn't be legible by the time the road has virtually disappeared what state might the road be in while the sign is still legible, both if the sign is still standing and if the sign has fallen (assuming being on the ground would hasten its decay or would the sign be illegible by the time it deteriorates enough to fall)?