The fact that train wheels wear out over time is a normal consequence of their use. However, things get complicated if the wear is more advanced. This can result in rough running, flat spots, microcracks or, at worst, shelling of the wheel. Even in the case of minor defects, vibrations occur, causing disturbing noises in the passenger compartments. If defects are not detected and rectified early enough, there is a risk that the vehicle's bogie will suffer damage eventually. In the worst-case scenario, not only would the train break down, but traffic on the route could also be severely congested because, for safety reasons, the vehicles may only return to the depot at a reduced speed – or, under certain circumstances, it even has to be hauled.
