| Abbreviation | Definition |
|---|---|
| ARJX | Arch Chemicals |
| ARL | Airport Rail Link |
| ARL | Armour Refrigerator Line |
| ARLU | A&R Logistics |
| ARMD | Arnaud Railway |
| ARMH | Missouri Pacific Railroad (Union Pacific Railroad) |
| ARMH | Union Pacific Railroad Company |
| ARMN | Missouri Pacific Railroad (Union Pacific Railroad) |
| ARMN | Union Pacific Railroad Company |
| ARMX | American Rail and Marine Corporation |
| ARMZ | Armasal Line |
| ARN | Alberta RailNet (Canadian National Railway) |
| AROX | Arro Oil & Refining (GATX Corporation) |
| AROX | General American Transportation Corporation |
| ARPS | Adirondack Railway Preservation Society |
| ARPX | Arco Petroleum Products (BP Products North America) |
| ARPX | Arco Products Company - Div of Atlantic Richfield Company |
| ARR | Alaska Railroad |
| ARR | Alaska Railroad Corporation |
| ARRC | Advanced Railway Research Centre |