This thesis examines the effect of vehicle dynamics on both vertical and lateral deterioration ofrnthe track alignment. The track system, the measurements of the track geometry and the definitionrnof the track quality are explained in detail. The background study forms fundamental knowledgernfor the vehicle-track lateral dynamic interaction study. A review of current researches in thernfield of vertical and lateral railway track deterioration is presented in order to establish a betterrnunderstanding of track deterioration mechanisms, highlighting the weakness and limitations ofrnthese studies.rnBased on the background and the reviews done in the field, the statistical analysis is done andrnprovides a better understanding of three aspects of track lateral irregularities: the relationshiprnbetween vertical and lateral irregularities, the relationship between track curvature and trackrnlateral irregularity and the change in track lateral deterioration over time.rnThe paper describes statistical studies of track deterioration, as well as the development andrnvalidation of a vehicle-track dynamic interaction model so that making the effective control andrnreduction of the lateral deterioration achievable and the vertical and lateral track irregularityrnmagnitudes are clearly correlated. The model indicates the mechanisms influencing trackrndeterioration both vertically and laterally which provides effective solutions in consideration ofrnvehicles, wheel-rail contact and the track system.