Road and track irregularities have an important influence on the dynamic behaviour of vehicles.Knowledge of their characteristics and magnitude is essential for the design of the vehicle but also for comparable homologation and acceptance tests as well as for the planning and management of track maintenance. Irregularities of tracks and roads are regularly measured using various measurement technologies. All have advantages and weaknesses and require several processing steps. Characterisation of irregularities is done in the distance as well as in the wavelength domain. For rail irregularities, various distance domain description methods have been proposed and are in use. Methods have been analysed and compared with regard to their processing steps. Several methods have been analysed using measured irregularity and vehicle response data. Characterisation in the wavelength domain is done in a similar way for track and road irregularities. Here, an important issue is the estimation of the power spectral densities and the approximation by analytical formulas. For rail irregularities, periodic defects also play an important role. The use of irregularities in simulations requires various processing steps if measured irregularities are used, as well as if synthetic data are utilised. This paper gives a quite complete overview of rail irregularities and points out similarities and differences to the road.

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Vehicle-track interaction in railway operation is highly influenced by physical processes within the wheel-rail contact. Thus, accurate prediction models describing these processes are of high importance. Such models have to take into account the plasticity phenomena appropriately because such phenomena generally occur in the near-surface layers of wheels and rails in railway operation. Within the contact zone, two plasticity effects occur: 'global' plastification in the order of hundreds of microns up to millimetres due to the general loading situation and 'tribological' plastification in the order of microns due to surface effects (e.g. roughness) which is always accompanied by the wear process. State-of-theart models do not take into account these effects sufficiently. The main ideas of the so-called overall wheel-rail contact and damage model taking into account the mentioned plasticity phenomena are presented together with typical results of the model.

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