The Combined Nomenclature (CN), v1:2022
8604 00 00: Railway or tramway maintenance or service vehicles, whether or not self-propelled, e.g., workshops, cranes, ballast tampers, trackliners, testing coaches and track inspection vehicles
https://www.dst.dk/en/Statistik/dokumentation/nomenklaturer/kn?id=a2a52813-81e3-4448-b7d4-12b366c09580