| Abbreviation | Definition |
|---|---|
| INT | Norfolk Southern Railway Company (formerly Interstate Railroad Company) |
| INTC | Interchange |
| INTS | Interlake Steel |
| INTU | Interpool Container Pty |
| INTU | Interpool Container Pty Limited |
| INTZ | Interpool |
| INTZ | Interpool Limited |
| INVI | Indianapolis & Vincennes Railroad |
| INYU | Infinity Transportation Logistics |
| IOCR | Indiana and Ohio Central Railroad |
| IOCR | Indiana Ohio Central Railroad |
| IOCX | Illinois Oil Co. (Rail Enterprises) |
| IOCX | Rail Enterprises Incorporated (formerly Iron Ore of Canada Railroad) |
| IOER | Indiana & Ohio Eastern Railroad, Inc. |
| IOLU | Textainer Equipment Management |
| IOLU | Textainer Equipment Management, Limited |
| IOPX | Iowa Power and Light (MidAmerican Energy) |
| IOPX | MidAmerican Energy Company (formerly Iowa Power & Light) |
| IOPZ | Iowa Public Service |
| IORX | Indiana & Ohio Rail Passenger |