In a railway, the vehicle interacts dynamically with a track superstructure (rails, rail pad and sleepers) and sub-structure (ballast, sub-ballast, sub- grade). Passengers' comfort, environmental loading (ground vibration) and frequency of maintenance works of vehicles as well as of the track are deter- mined by the way all the structural elements interact. The response of each single structural component is sensitive to the wheel-axle pressure on the track, the effects of joint in un welded rails, the unevenness of wheel and rail, and the train speed as referred to the track critical velocity (minimum phase velocity of bending waves propagating in the track rails, supported by the ballast). An important issue is for example how the ballast will be affected when old, soft, timber sleepers and replaced by much, stiffer, pres- tressed concrete elements, and how newly introduced irregularities propa- gate along the track, among uncountable mathematical model possibilities, the presents a rail-pad-sleeper-ballast model mainly based on an assemble of Timoshenko beam elements (for the rail) including, in case of the sle- epers, elastic foundation (for the ballast) and viscous damping. The local interaction of the rail-pad-sleeper set is simulated with a bar element that includes damping. The dissertation reports on the numerical model, which relies on exact, dynamic beam and truss elements derived on a variational basis for the frequency-domain analysis. The model enable the assessment of the vibration characteristics of a rail track, the inverse evaluation of se- veral mechanical properties of the structural components and eventually, if everything goes well, the assessment of a dynamic behavior of the rail track actual service load. Theoretical basis for transient analysis is the advanced mode superposition technique. Finally, are proposed three global models for the railway, obtained considering some modifications in the sleeper.