The topic of this PhD thesis is active suspension in rail vehicles whichis usually realized through sensors, controllers and actuation components.A well established example of an active suspension is the tiltingcontrol system used to tilt the carbody in curves to reduce centrifugalacceleration felt by passengers. Active suspension for rail vehicles is beingstudied since 1970s and in this PhD thesis it has been tried to expandon some aspects of this topic.This study extends the research field by both experimental and theoreticalstudies. In the first phase of the study which led to a licentiatedegree the focus was more on experimental work with active verticalsuspension (AVS). This was implemented by introducing actuators inthe secondary suspension of a Bombardier test train, Regina 250, in thevertical direction. The aim has been to improve vertical ride comfort bycontrolling bounce, pitch and roll motions.In the second phase after the licentiate, the studies have been moretheoretical and can be divided into two parts. The first part of the workhas been more focused on equipping two-axle rail vehicles with differentactive suspension solutions for improving the vehicle performanceregarding comfort and wheel-rail interaction. Three papers are writtenon active suspension for two-axle rail vehicles. Two of the papers discussthe use of H¥ control for wheelset guidance in curves to reducewheel-rail damage. The third paper shows that by use of active verticaland lateral suspension (AVS and ALS) in two-axle rail vehicles goodcomfort can be achieved as well. The paper then studies how the threeactive suspension systems (ALS, AVS, and ASW) interact once implementedtogether on a two-axle rail vehicle.The second part is a study on safety of active suspension systems.The study discusses a possible procedure to ensure that a designed activesuspension for a rail vehicle will be safe in all possible failure situations. / <p>QC 20170602</p>