| Abbreviation | Definition |
|---|---|
| NMOR | Northern Missouri Railroad |
| NMRC | Noida Metro Rail Corporation |
| NMRX | New Mexico Department of Transportation |
| NMSX | New Mexico Steam Locomotive and Railroad Historical Society |
| NN | Nevada Northern Railway |
| NN | Northern Nevada Railroad Corporation |
| NNCU | Canadian Royalties |
| NNIU | Nautica Line |
| NNPU | Nigerian National Petroleum Corporation |
| NNSX | Newport News Shipbuilding and Dry Dock |
| NNSX | Newport News Shipbuilding and Dry Dock Company |
| NNW | Nebraska Northwestern Railroad |
| NNYX | National New York Central Railroad Museum |
| NODM | Mexico North Western |
| NOFU | Nodfos |
| NOGC | New Orleans and Gulf Coast Railway |
| NOKL | Northwestern Oklahoma Railroad |
| NOKL | Northwestern Oklahoma Railroad Co |
| NOKR | Northwestern Oklahoma Railroad |
| NOKZ | First Union Rail |