| Abbreviation | Definition |
|---|---|
| IDTU | Hawaii Intermodal Tank Transport |
| IEAU | Intermodal Equipment Associates |
| IELZ | Iran Express Lines |
| IERR | Indiana Eastern Railroad, LLC |
| IES | Intra-Europe Service |
| IESX | IES Utilities Incorporated |
| IESX | IESX Corporation (Alliant Energy) |
| IFBX | General Electric Railcar Services Corporation |
| IFBX | Indiana Farm Bureau Cooperative Association (GE Rail Services Corporation) |
| IFCX | Interstate Foods Corporation |
| IFLU | Interflow |
| IFOX | Industrial Fuel Oil |
| IFRX | Infinity Rail |
| IFSU | Interlink Freight Systems |
| IFWZ | Independent Freightway |
| IFWZ | Independent Freightway Incorporated |
| IGCZ | Indiana Grain Company |
| IGMQ | Integrated Grain And Milling |
| IGN | International-Great Northern |
| IGPX | Industrial Steam Products |