In recent decades, rail transport has become a popular mean of transportation due to its efficiency and environmental friendliness technology which lead to increasing the axle loads, speed and recurrence of the trains. These enhanced service provisions resulted in new challenges to the sustainability of the railway systems. Insulated rail joint (IRJ) is one of the crucial structural components of the railway track with the function of serving the signaling control by securing the occupancy of the track with one and only train in each divided block. An IRJ includes the application of two joint bars being bolted with the purpose of connecting two adjoining rails. In addition to the insulation layers between the joint bars and the rail, the end post which is positioned between the end-to-end rails, assure the disruptions of current flow between two blocks. The emerge of discontinuity in the stiffness and geometry at IRJs influence the service life of this component due to the introduced high dynamic forces. Subsequently, the IRJ is considered as one of the weak spots of the railway tracks which requires the allocation of great concern in their maintenance. In order to attain understanding of the wheel-rail dynamic interaction at IRJs, various analytical, experimental and numerical studies have been conducted in the past few years. The application of the finite element method (FEM), as a flexible numerical tool, reveals distinct advantages for understanding the behavior of the track structure under the pass-by wheel. This M.Sc. thesis utilizes an explicit finite element analysis to investigate the influence of the sleeper spacing and traffic speed on the impact force and vibration of the track. The FE model includes the detailed demonstration of the rail, joint bars and sleepers while simulated spring and damper elements are preferred to the rail pads and ballast to reduce the complexity of the model. Besides, the detailed illustration of the wheel and axle as well as the effects of the carbody and bogie are considered in the FE model. Based on the parametric studies conducted in this thesis, the impact force as well as the low (0–3kHz) and high (3-10kHz) -frequency vibrations are prominently influenced by the application of non-uniform sleeper spacing and various traffic speed. With considering the two factors; sleeper spacing and traffic speed, a typical statistical approach -Design of Experiment- is implemented to attain an optimized track model with the aim of reducing the impact force and the impact vibration of the track, and thus to reduce the maintenance necessity and noise generation as well as to increase the passenger comfort. The performance of the nominated optimized model has been observed under the application of two typical trains operated on the Dutch railway network. Finally, the conclusions are presented and recommendations for future research are proposed.