| Abbreviation | Definition |
|---|---|
| IHAU | Ihora Chemical Industrial |
| IHB | Indiana Harbor Belt Railroad |
| IHB | Indiana Harbor Belt Railroad Company |
| IHC | IHC Industry |
| IHCU | CSD Assignment |
| IHCX | Indian Head Central Railway |
| IHMZ | Indian Head Mining Company |
| IHOU | Intermodal Tank Transport |
| IHRC | Indiana Hi-Rail Corporation |
| IHRT | Indian Head Rail Trail |
| IHSX | Alberni Pacific Railway (Western Vancouver Island Heritage Society) |
| IHSX | Western Vancouver Island Heritage Society (Alberni Pacific Railway) |
| IICZ | Illinois Central Railroad (Canadian National Railway) |
| IIIU | III Transportation |
| IIIZ | III Transportation |
| IILU | Independent Container Line |
| IILZ | Independent Container Line |
| IIRC | Indiana Interstate Railway |
| IIRC | Indiana Interstate Railway Company, Inc. (was INDI) |
| IIRR | Iranian Islamic Republic Railways |