This paper initially describes the main features of the radial selfsteering bogies, which have been developed for the high speed train X2000. suburban trains and other applications. One of the main goals with these bogies is to reduce lateral track forces at high speed curving.This development has been supported by extensive theoretical investigations parallel to practical tests and verifications. Since around 1973 the main tool for theoretical analysis has been time domain simulations of non-linear vehicle-track models under influence of perfect and irregular track geometry. There are models for verticaVlongitudinal and for lateral dynamics. The models are assembled and utilised in a specialised computer program, SIMFO, and in a more general computer code, GENSYS, the latter having full 3-dimensional capability. A frequently used model for lateral dynamics of a four-axle bogie vehicle with 37 degrees of freedom (DOF) is shown as an example. In order to avoid an unrealistically stiff lateral coupling between wheel axles and ground, this model contains lateral track-ground elasticity and I or lateral and torsional DOF for each wheel. By comparison with measurements it is shown that characteristic quasistatic and dynamic behaviour can be simulated with accuracy.

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The rail network of Sweden is characterized by frequent curves, which limit the speed of conventional rolling stock to moderate levels. Speed of travel is, however, probably the most important factor in competition between different modes of transport, both now and in the future. For economic reasons the existing track must be used, with minimum modifications. Effort in Sweden has therefore been concentrated on the development of a new technology, making it possible to run at 35–60 per cent higher speeds on existing track. At these higher speeds comfort levels and track forces must not be worse than for current rolling stock running at present speeds on the Swedish main line track. In order to satisfy these requirements, future vehicles must be equipped with car body tilting, and must also exhibit food dynamic interaction with irregular track. Swedish State Railways (SJ) and ASEA have jointly developed and tested a new concept, including hydraulic or pneumatic car body tilting and radial steering bogies. These bogies allow for high speed through curves without excessive lateral forces and the associated wear on wheels and rails. In this bogie it has been possible to optimize primary suspension and damping parameters so as to maintain stability without hunting at speeds of up to at least 200 km/h. An experimental train set, type X15, was the subject of extensive tests during the period 1975–82. The design of the bogies and car body tilting systems has been supported by computer simulation programs. New methods of analysis have been developed and validated as an integral part of the development project. The simulation technique has proved to be very useful and accurate in the prediction of vehicle dynamic behaviour. Also some tests of passengers' opinions on comfort in tilting trains have been carried out.