| Abbreviation | Definition |
|---|---|
| ASRY | Ashland Railway |
| ASRY | Ashland Railway Incorporated |
| ASRZ | Agri/Share Cooperative |
| ASTX | ASARCO |
| ASTX | Asarco Incorporated |
| ASYX | Avondale Shipyards |
| AT | Auto Train |
| AT&SF | Acheson, Topeka, Santa Fe Railroad |
| AT&SF | Acheson, Topeka, & Santa Fe Railroad |
| ATAX | Arizona Transit Assembly (Alameda Corridor Transportation Authority) |
| ATC | Atlanta Transit Company |
| ATCO | Arnold Transit |
| ATCX | Austin and Texas Central Railroad (Southern Illinois Railcar) |
| ATCX | Southern Illinois Railcar Incorporated |
| ATEX | Asplundh Tree Expert |
| ATEX | Asplundh Tree Expert Company Railroad Division |
| ATGU | BNSF Railway |
| ATGU | Burlington Northern and Santa Fe Railway Company |
| ATGX | ATEL Leasing Corporation |
| ATIU | Societe Auxiliaire De Transport et D'Industries |