| Abbreviation | Definition |
|---|---|
| ATIU | Societe Auxillaire De Transport Et D'Industries |
| ATIX | Alstom Transportation |
| ATLT | AT and L Railroad Company |
| ATLT | AT&L Railroad |
| ATLU | American Marine Industries |
| ATLX | Atlas Machine and Iron Works |
| ATLX | Atlas Machine and Iron Works Incorporated |
| ATLZ | American Marine Industries |
| ATMX | U.S. Department of Energy Albuquerque Office |
| ATMX | United States Department of Energy Albuquerque Operations (Arcelor Mittal Montreal) |
| ATN | Alabama & Tennessee River Railway |
| ATOC | Association Of Train Operating Companies |
| ATOU | Atochem |
| ATP | Automatic Train Protection |
| ATR | Alliance Terminal Railroad |
| ATRW | Anthracite Railway |
| ATSF | Atcheson Topeka Santa Fe |
| ATSF | Atchison, Topeka and Santa Fe Railway (BNSF Railway) |
| ATSF | Burlington Northern and Santa Fe Railway Company |
| ATTX | American Turpentine & Tar (TTX Corporation) |