| Abbreviation | Definition |
|---|---|
| ACR | Algoma Central Railway (Snow Train) |
| ACRC | Andalusia and Conecuh Railroad |
| ACRE | Anti Corridor Rail Expansion |
| ACRI | Australasian Centre for Rail Innovation |
| ACRR | Augsburg & Concord Railroad |
| ACRRA | Anoka County Regional Railroad Authority |
| ACRX | American Chrome and Chemicals (Elementis Chromium) |
| ACRX | American Chrome and Chemicals Incorporated |
| ACSU | Atlantic Cargo Services A B |
| ACSU | Atlantic Cargo Services, AB |
| ACSX | Allied Chemical (First Union Properties) |
| ACSX | First Union Properties Incorporated |
| ACSZ | American Carrier Equipment |
| ACT | Absolute Constant Time |
| ACTU | Associated Container Transport (Australia) |
| ACTX | Allied Chemical (Honeywell International) |
| ACTX | Allied Chemical Company (Allied Corporation) |
| ACUU | Acugreen Limited |
| ACWR | Aberdeen Carolina and Western Railway |
| ACWR | Aberdeen, Carolina and Western Railway |