| Abbreviation | Definition |
|---|---|
| SUN | Sunderland |
| SUN | Sunset Railway |
| SUN | Sunset Railway Company |
| SUNX | Sun Refining and Marketing |
| SUNX | Sun Refining and Marketing Company |
| SUR | State University Railroad |
| SUTU | Suttons International |
| SUTX | Sumter Transport |
| SV | Greater Shenandoah Valley Development (Shenandoah Valley Railroad) |
| SV | Greater Shenandoah Valley Development Company - Shenandoah Valley Railroad |
| SVGX | Savage Services |
| SVI | Southern Railway of Vancouver Island (E and N Railway) |
| SVIL | Saltville Railroad |
| SVIX | Shelbyville Industrial Railroad |
| SVRR | Shamokin Valley Railroad |
| SVRR | Shamokin Valley Railroad Company |
| SW | Southwestern Railroad |
| SW | Southwestern Railroad Company |
| SWCX | Estech |
| SWFX | Southwest Forest Industries |