While The Walking Dead television show has been on for 7 years, the actual passage of time is highly debatable and certainly not discernible from the condition of the pavement. With seasons starting and finishing and the southern climate not varying hugely it is difficult to determine how much time should have passed. There are places where plants have overgrown large areas but I’m amused to find that pavement maintenance must be happening and the roads offer a pretty smooth ride.
With the exception of dead cars, walkers and corpses littering the highway, most roads are fairly passable. There are not a lot of potholes or wear on the highways. I know there isn’t a lot of traffic left but there should still be a lot of rain in the post-apocalyptic south. There are no street crews seal-coating or filling cracks. There is no department of transportation sealing the joints on bridges and highways.
What would happen if no one was around to maintain asphalt or concrete? Rain would wash away the oils in asphalt. The aggregates in asphalt would become exposed. Cracks would form and branch. If rain gets in those cracks and it is cold enough for a freeze, the water in those cracks would freeze, expand and widen the cracks. In the fertile south, plants would grow in those cracks. The roots would grow and further push apart the asphalt. Potholes would multiply.
Concrete might fare better than asphalt in a post-apocalyptic world, at least if it had been maintained at the start. With no traffic, any existing concrete cracks probably wouldn’t expand as quickly. Metals in reinforced concrete would still suffer from corrosion and the freeze-thaw cycle could damage concrete. The bodies themselves left on the concrete could cause corrosion and damage during decomposition. The roads in Walking Dead should probably be in worse shape.
I don’t expect to see any zombies in the near future but the reality is, pavement maintenance is essential, no matter what the situation.