The railway track is a complicated construction with many components that affect the trains in various ways. The track flexibility is an especially important issue when it comes to train-track interaction, but in simulations many models today do not pay special attention to it. There is therefore a need for a better understanding of this field and what effects the track flexibility has on the vehicle dynamics behavior.

After investigating some existing track models, this thesis proposes new track flexibility models. For the proposed track models the number of degrees of freedom is a central factor. Some track receptance data from measurements done by Banverket are reported and various parameters' effects on the track's flexibility are assessed. The track data from the measurements are then compared to receptances of the proposed track models.

A Regina train model is used to simulate runs over a track and the wheel-rail forces are analysed. The program used for the simulations is the multibody dynamics program GENSYS. It is shown that the flexibility of the track effects the wheel-rail forces significantly. The main conclusion drawn is that the flexibility is important and can not be overlooked in models of train-track interaction.