| Abbreviation | Definition |
|---|---|
| ITRM | Iowa Terminal Railroad Company, Mason City Division |
| ITRU | Itel Containers International Corporation |
| ITRZ | Interrail Transport |
| ITSJ | Intermodal Transportation Services |
| ITSL | ITS Technologies & Logistics |
| ITSU | Iberhansaetic Transport System |
| ITSX | In-Terminal Services |
| ITSZ | International Transportation Service |
| ITSZ | ITS Maersk (formerly International Transportation Service Incorporated) |
| ITTR | ITT Rayonier Railrod |
| ITTX | Trailer Train (TTX Corporation) |
| ITTX | TTX Company |
| ITXU | Interport Maintenance |
| ITXX | Impulsora Tlaxcalteca de Industrias (Tlaxcalteca de Industrias de CV) |
| ITXX | Tiaxcalteca de Industrias, S. A. de C. V. |
| IU | Indianapolis Union |
| IU | Indianapolis Union Railway |
| IVCR | Illinois Valley Commuter Rail |
| IVCX | Invista S.A.R.L. |
| IVLU | Ivarans Rederei |