It is well known that defective wheels and/or irregularities of the rails generate impact forces. Generally vertical impact forces are determined using either field measurement or 2D simulation models. As part of ongoing research on degradation of wagon-track system, a three-dimensional wagon - track system dynamics (3DWTSD) model with the potential to predict the simultaneous occurrence of vertical and lateral impact forces has been developed at the Centre for Railway Engineering. The influence of two important track parameters, namely, the sleeper spacing and the ballast depth to the dynamic impact has been examined using the 3DWTSD model and presented in this paper. The peak vertical and lateral impact forces at the wheel-rail contact patch, and the vertical impact force at the pad, the ballast, the subballast and the sUbgrade are reported in addition to the peak displacements of the track components. The results show that the larger spacing of the sleepers and the lower depth of ballast produce soft track condition which leads to larger track deflection and smaller wheel-rail impact forces.