The problem of track-bridge interaction and its modeling issues have increasingly been emphasized and highlighted due to the presence of high-speed rails. The quality criteria for high-speed rail lines must be stricter than those for conventional rail lines to assure passenger comfort and safety. Experience shows that in transition zones when a train rides from an embankment onto a stiff structure, such as a bridge, tunnel or culvert, an abrupt change occurs in the support stiffness possibly inducing differential settlements. Examples prove that inadequate technical solutions can generate damage that may require long term speed restrictions or lead to short maintenance cycles, significantly increasing the total cost of ownership. The problems associated with the transition zones require complex analysis. The author reports the results obtained by the investigation of a 3D numerical model of a bridge transition zone by means of an advanced constitutive model and time domain analysis. The mechanical behavior of a railway bridge and its soil environment is presented in the study with special regards to factors like train speed, embankment height and the settlement differences apparently developing in the transition zone.