The effects of interface condition and horizontal wheel loads on the life of flexible and semirigid pavements were determined. The methodology consisted of implementing a previously derived interface constitutive model into the ABAQUS finite element program to compute the stresses and strains in typical flexible and seimrigid road structures. The Shell transfer functions for fatigue cracking and terminal serviceability were used to estimate the life of the two pavements. The study revealed that the horizontal loads acting at the pavement surface lead to dramatically increased tensile strains at the top and bottom of the wearing course and at the top of the binder course. This may justify the initiation of cracking at the surface of the pavement and not at the bottom of the asphalt layer, as generally assumed. For semirigid pavements, the condition of the wearing-binder course interface affects the strains in the wearing course, whereas the condition of the binder-base interface affects the horizontal strain field in the binder layer more as well as the vertical strains at the top of the subgrade. For flexible pavements, the condition of the interface between the wearing and binder courses dramatically changes the strain field in the wearing and binder layers and increases the vertical strains at the top of the granular base and subgrade layers. The cumulative effect of the interface condition and horizontal forces acting at pavement surface is expressed by a dramatic reduction in pavement life, especially for the semirigid pavement.