Gradual accumulation of permanent deformations in railway track embankments caused by repeated train axle loads is an important problem in the Northern areas, where the track embankments must be built very thick because of design against harmful effects of seasonal frost. Based on long-term measurements performed at a test site located in Western Finland, both embankment width and slope angle are shown to have a marked effect on the accumulation rate of permanent deformations. The observed differences can be given a credible explanation when the results of 2D Finite Element Modelling are interpreted based on the mobilized level of shear strain in embankment sections with different width and slope angle.