The Combined Nomenclature (CN), v1:2018
8604 00 00: Railway or tramway maintenance or service vehicles, whether or not self-propelled, e.g., workshops, cranes, ballast tampers, trackliners, testing
https://www.dst.dk/en/Statistik/dokumentation/nomenklaturer/kn?id=97dd4f6e-1b47-43b5-8532-380d3d1b7c2f