This past winter, my concrete driveway heaved 1.5" above where it meets the garage floor. It is three years old. Also, we dug along the sides of the drive to try to guage if a 4" slab was actually poured- discovered many crevices on the side. Could this cause a problem later? Specifically cracking?
Frost heaves are caused by water in the ground freezing and pushing up. The thickness of the slab has nothing to do with it. The force caused by ice expanding when it freezes is huge, and it's almost certainly not practical to resist it. Better to remove the force in the first place.
There are only two ways to prevent frost heaving, and neither is perfect:
Dig down below the frost line. This is obviously not practical for a driveway. (Also, even a foundation whose bottom is below the frost line may be susceptible to heaving if water can freeze around the sizes and pull it up.)
Reduce the amount of water underneath the structure with grading, drains, etc. A properly-prepared subsurface can also help here by reducing the water content of the soil
What is the drainage situation like around your driveway?