| Abbreviation | Definition |
|---|---|
| A | Alton Railroad |
| AA | Ann Arbor Railroad |
| AAAX | AAA Warehouse Corporation (Shell Oil) |
| AACX | Alaska Division of Agriculture |
| AADX | Airco Alloys and Carbide |
| AAEX | American Aniline and Extract |
| AAIX | ACS International Inc |
| AAKX | Amulco Asphalt |
| AALX | Advanced Aromatics, LP |
| AAMX | ACF Industries Shippers Car Line Division |
| AAMX | ACFA Arrendadora de Carros de Ferrocarril S. A. |
| AAR | American Association of Railroaders |
| AAR | American Association of Railroads |
| AAR | Association of American Railroads |
| AARS | American Association of Railroad Superintendents |
| AARX | Association of American Railroads |
| AATX | Ampacet Corporation |
| AAX | American Agricultural Chemical (Agrico Chemical) |
| AB | Akron Barberton Cluster Railway |
| AB | Akron Barberton Cluster Railway Company |