| Abbreviation | Definition |
|---|---|
| ABOX | Railbox Company |
| ABPR | Aberdeen and Briar Patch Railway (Aberdeen, Carolina and Western Railway) |
| ABPX | Ashland By-Product Coke (Animal By-Products Corporation) |
| ABR | Athens Line |
| ABRX | AB Rail Investments (Railmark Holdings) |
| ABRX | AB Rail Investments Incorporated |
| ABS | Alabama Southern Railroad |
| ABSX | American Beet Sugar (Albert Brothers Inc) |
| ABTX | Aubrey Bartlett (General Electric Railcar Services Corp.) |
| ABWX | Asea Brown Boveri |
| ABWX | Asea Brown Boveri Incorporated |
| ABX | Adirondack Bottled Gas Corporation (Home Gas Corporation of Great Barrington) |
| AC | Algoma Central and Hudson Bay Railway (Algoma Central Railway) |
| AC | Algoma Central Railway Incorporated |
| ACAX | Allied Chemical Company (Allied Corporation) |
| ACAX | Aluminum of America (Alcoa) |
| ACBL | American Commercial Barge Lines |
| ACBX | American Cast Iron Pipe |
| ACCU | Atlantic Coast Container Brokerage & Sales |
| ACCX | Ansul Chemical (Consolidation Coal) |