Rate of deterioration for asphalt/blacktop and road signs [duplicate]

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)?

• This question belongs on WorldBuilding SE, as noted. – Lauren Ipsum Nov 20 '15 at 10:44
• You're right! First time poster, sorry about that. Will see what I can do about moving the question. Thanks!! – J.R. Nov 20 '15 at 13:51
• I'll migrate it for you. – Monica Cellio Nov 20 '15 at 19:56
• Someone wrote a book about how long the nature takes to reclaim and deteriorate man-made structures: en.wikipedia.org/wiki/The_World_Without_Us I think that you could read the book or some online synopsis for your world building – Silver Nov 20 '15 at 21:05
• Thanks @MonicaCellio but I did already and it's been shot down and put on hold. Curiously enough I've received some good answers HERE that move me in the right direction while being put on hold in worldbuilding for not being specific enough. sigh – J.R. Nov 20 '15 at 21:17