Each European country has regulations concerning crashworthiness and only allows compliant rolling stock on its network. The European Commission is engaged in a long-term effort to harmonise these regulations. A central basis for crashworthiness requirements is risk analysis that takes account of statistics on past collisions at each of a range of speeds. This helps explain why the US requires better crashworthiness in railway vehicles than in Europe: collisions and overspeed derailments are more frequent per train-km in the US than in Europe because historically, US signalling systems have tended to provide speed supervision and automatic train stop on fewer lines than in Europe. (This is slowly changing with the implementation of PTC.) The result of risk analysis is trains (and planes) that are crashworthy, but only to a limited extent.
This is a rough sketch of my understanding of the situation; comments are welcome.
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