| Abbreviation | Definition |
|---|---|
| SIRA | Systems Integration for Railways Advancement |
| SIRC | Staten Island Railroad |
| SIRR | Southern Industrial Railroad |
| SIRS | Shelbyville Industrial Rail Service |
| SIRX | Southern Illinois Railcar Company |
| SIRX | Southern Illinois Railcar Corporation |
| SISU | Scandinavian Cargo Sea AB |
| SISU | Scandinavian Cargo Sea, A. B. |
| SITX | Sherritt International Corporation |
| SJEX | SJEX Inc. |
| SJEX | SJEX Incorporated |
| SJMX | St. Joe Minerals Corporation |
| SJNX | Mobay Corporation |
| SJRT | St. Johns River Terminal |
| SJRX | Jacksonville Electric Authority |
| SJRX | St. Johns River Railway |
| SJSZ | Specialty Chassis Leasing |
| SJSZ | Specialty Chassis Leasing Incorporated |
| SJT | St. Joseph Terminal Railroad |
| SJVR | San Joaquin Valley Railroad |