Yes agree very much, its accumalitive passes, but also the hydroscopic effect as heavy axles pass over sodden weak surfaces, ie mainly sand, water is pumped under pressure and causes the matrix to break up. This causes rapid breakup, also the more uneven a surface the great the stresses and strains, hence smoother roads last longer and are measured for smoothness as a contractor lays the asphalt. I know this is the most basic of road structures but these criteria still apply