| Abbreviation | Definition |
|---|---|
| IRS | Independent Rear Suspension |
| IRT | Interborough Rapid Transit |
| IRT | Interborrough Rapid Transit |
| IRTB | Illinois Road and Transportation Builders |
| IRTU | International Road Transport Union |
| IRU | Interactive Response Unit |
| IRV | Immediate Response Vehicle |
| IRV | Insightful Recreational Vehicle |
| ISA | Intelligent Speed Adaptation |
| ISAD | Integrated Starter Alternator Damper |
| ISARP | IOSA Standard and Recommended Practice |
| ISB | Inter-State Bus |
| ISBT | Inter-State Bus Terminal |
| ISC | Idle Speed Control |
| ISD | In Some Direction |
| ISD | Interim Simulation Display |
| ISDE | International Six Days Enduro |
| ISDP | Integrated Ship Design and Production |
| ISIS | Integrated Shock Isolation System |
| ISIS | International Suspension Interface System |