Freeware: https://rail-sim.de/forum/filebase/entry/10781-u4-u5-wagen-verbesserte-zza/

https://rail-sim.de/forum/filebase/entry/4795-bombardier-flexity-swift-typ-u5-replacement-sound-1-0/

https://railomanie.eu/filebase/entry/71-tdr-signaltafelset5/