With a view to examining the dynamic responses of the wheel-rail interface, a three-dimensional wagontrack system dynamics (3D WTSD) model was developed and presented widely in the literature by the authors in recent times. The 3D WTSD model consists of three subsystems, namely, a 37 degree-of freedom (DOF) wagon subsystem, a wheel-rail interface subsystem and a four-layer track subsystem. This paper presents the application of the 3D WTSD model to the examination of the effect of track geometry irregularities on the lateral and vertical dynamic impact forces. The simulated dynamic responses at the wheel-rail interface due to some geometric irregularities, namely, the ariation of cross level and gauge are presented. The characteristics of the dynamic responses due to these track irregularities are examined. The sensitivity of the dynamic responses to the variation of cross level and gauge are also presented. It is shown that when the wavelength of cross level irregularity was less 2 m, the vertical impact force exhibited higher rates of increase. It is also shown that the derivation of the gauge face of the rail in the plane of track has pronounced effect on the (L/V) ratio.