| Abbreviation | Definition |
|---|---|
| NICU | NIC Leasing |
| NICU | NIC Leasing Incorporated |
| NICX | Niles Canyon Railway |
| NIFX | GE Rail Services |
| NIFX | General Electric Railcar Services Corporation |
| NIHX | GE Rail Services |
| NIHX | General Electric Railcar Services Corporation |
| NIKX | N. I. K. Non-stock Marketing Cooperative |
| NIKX | NIK Non-stock Marketing Cooperative |
| NIL | North Island Line |
| NIMX | Naporano |
| NIPRA | Northeast Indiana Passenger Rail Association |
| NIPRA | Northern Indiana Passenger Rail Association |
| NIRX | GE Rail Services |
| NIRX | General Electric Railcar Services Corporation |
| NITX | Nitram |
| NITX | Nitram Incorporated |
| NIWX | Northern Illinois & Wisconsin Railway Corporation |
| NIWX | Northern Illinois and Wisconsin Railway |
| NJ | Delaware and Hudson Railway Company Incorporated |