| Abbreviation | Designation | |
|---|---|---|
| R | REGIO (Polish) REGIO (Poland) | train category |
| REG | Rail Europe Group | company |
| R.E.G. | Rheinische Eisenbahn-Gesellschaft (German) | railway company |
| R.E.G. | Kgl. Direction der Rheinischen Eisenbahn (1880–1881), Königliche Direction der Rheinischen Eisenbahn in Cöln (German) Royal division of the Rhenish Railway Company | railway administration |
| Reg | Regensburg (1907–1976) (German) | railway administration |