The Combined Nomenclature (CN), v1:2019
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=f5446a47-febf-4bd1-98b9-8e347fa96472