| Abbreviation | Definition |
|---|---|
| ACWZ | Chicago & North Western (Union Pacific Railroad) |
| ACWZ | Union Pacific Railroad Company |
| ACXU | Atlantic Cargo Services AB |
| ACXU | Atlantic Cargo Services, AB |
| ACXX | Anderson Columbia |
| ACXX | Anderson Columbia Company Incorporated |
| ACY | Akron, Canton and Youngstown Railroad (Norfolk Southern Railway) |
| ACY | Norfolk Southern Railway Company |
| ACZX | A C Railroad Service (Norfolk Southern Railway) |
| AD | Atlantic and Danville Railway (Norfolk, Franklin and Danville Railway) |
| ADBF | Adrian and Blissfield Rail Road Company |
| ADBF | Adrian and Blissfield Railroad |
| ADCU | Flexi-Van Leasing |
| ADCU | Flexi-Van Leasing Incorporated |
| ADCX | Adolph Coors |
| ADIR | Adirondack Railway |
| ADIR | Adirondack Scenic Railroad |
| ADIX | Adirondack Railway Preservation Society |
| ADKU | AGA A/S |
| ADMX | ADM Transportation Company |