This locomotive is available in multiple DLC routes (Rhein-Ruhr Osten and Hauptstrecke Rhein-Ruhr). As such, you can unlock this achievement in either DLC (though you will need Rhein-Ruhr Osten installed to be eligible).
This should be unlocked by travelling more than 70 km/hrin the BR 422 loco. Strangely, I unlocked this during a HRR service while travelling over 140 km/hr. Not sure if this is just because I was on a HRR route, but this is what worked for me. For those who have unlocked on a RRO route, please comment with the speed at which it unlocked.