The Combined Nomenclature (CN), v1:2023
8604 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=6288e2f3-11bf-4206-90bf-a3b6f6ebbc4d