| Abbreviation | Definition |
|---|---|
| UHRX | Upper Hudson River Railroad |
| UIC | Union Internationale des Chemin (International Union of Railways) |
| UIR | Indian River, Delaware, Delmarva Power |
| UIWX | Riley Stoker Corporation |
| UJH | Glassport, PA various consignees |
| UJL | Leetsdale, PA various consignees |
| UKC | Bath, Pennsylvania, Keystone Cement |
| UKD | Dover, Delaware, Kraft General Foods |
| ULGU | Universal Lng Solution |
| ULJ | Upsala- Lenna Jernveg |
| UMP | Upper Merion and Plymouth Railroad |
| UMPX | First Union Rail |
| UMPX | Upper Merion and Plymouth Leasing |
| UMSZ | Intermodal Services Incorporated |
| UMSZ | Maersk Equipment Services |
| UMXU | CSX Intermodal Inc |
| UMXU | CSX Transportation |
| UMXU | Union Pacific Railroad |
| UMXU | Union Pacific Railroad Company |
| UNBX | General Electric Rail Services Corporation |