The Combined Nomenclature (CN), v1:2021
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=49fd4a4b-3be3-4389-9b78-b2a56918d44c