In one way or another water and unsuitable base and sub-base materials are the main causes of road pavement failure. Water finds cracks in asphalt and PC concrete, soaks through to weaken the base materials or fills cracks and then freezes causing cracks to expand or break out due to expansion. Dealing with water effectively can greatly reduce road pavement failure.
For Portland cement concrete, using a capillary fill material for the base and sloping or crowning the roadway so any water that finds a way underneath the pavement can drain out without weakening the subgrade is one technique that has proven useful. Doing needed maintenance like sealing cracks and resurfacing asphalt with a sealcoat can also help greatly.
Dealing with weak sub grade materials can be a challenge, since this requires undercutting the roadway deep enough to encounter good, solid material, or installing several feet of good base to distribute the load over a wider area. In the past in our sandy soils in the Florida panhandle, clay was mixed with sand to strengthen the sub grade, and when blended to ideal proportions and compacted prior to adding limestone base underneath the pavement, it has worked well. Two other techniques were using asphalt sand and soil cement. Both mixed either asphalt or Portland cement into the top foot or so of the sand to strengthen it. This is a more expensive fix than adding clay, and isn’t common today.
There are lots of studies suggesting thicker pavement will also produce a more durable pavement. Since the actual materials are only a portion of the cost of building a road, it might make sense in some cases to pave roads thicker. An example would be paving asphalt roads 6 or 8 inches thick instead of 3 to 4 inches (in Florida, northern states pave thicker already) or to pour concrete pavement 10 to 14 inches thick instead of 6–10 inches. Since the machinery and workers are already on the project, the cost of adding this additional thickness weighs in mostly at added material cost, which may be a bargain on long-term maintenance costs.