| Abbreviation | Definition |
|---|---|
| NATU | Nasso SA |
| NATX | General Electric Railcar Services Corporation |
| NATX | North American Tank Line (GE Rail Services) |
| NATZ | North American Transportation |
| NAUG | Naugatuck Railroad |
| NAUG | Naugatuck Railroad Company |
| NAVE | Navajo Express |
| NAVE | Navajo Express Incorporated |
| NB | Northampton and Bath Railroad (Conrail) |
| NBCX | Nebraska Boiler |
| NBEC | New Brunswick East Coast Railway |
| NBER | Nittany and Bald Eagle Railroad |
| NBER | Nittany and Bald Eagle Railroad Company |
| NBIX | Bombardier Capital Rail |
| NBIX | NorRail Incorporated |
| NBNR | Nicolet Badger Northern Railroad |
| NBSR | New Brunswick Southern Railway |
| NBSR | New Brunswick Southern Railway Company Limited |
| NC | CSX Transportation Incorporated |
| NC | Nashville and Chattanooga Railroad (CSX Transportation) |