The Combined Nomenclature (CN), v1:2020
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=82f0fee5-2769-43bc-83fc-79117ee135ae