| Abbreviation | Definition |
|---|---|
| SPR | Southern Pacific Railroad |
| SPRINT | Southern Pacific Railroad Internal Network Telecommunications |
| SPRX | Seaport Central Railroad |
| SPRX | Seaport Central Railroad Incorporated |
| SPS | Burlington Northern and Santa Fe Railway Company |
| SPS | Spokane, Portland and Seattle Railway (BNSF Railway) |
| SPSX | Progress Rail Services Corporation |
| SPTX | Trinity Rail Management |
| SPTX | Trinity Rail Management Incorporated |
| SPTZ | Southern Pacific Railroad (Union Pacific Railroad) |
| SPTZ | Union Pacific Railroad Company |
| SPUD | St. Paul Union Depot |
| SPUD | St. Paul Union Depot Company |
| SPURT | Self Propelled Ultrasonic Rail Testing |
| SQVR | Sequatchie Valley Railroad |
| SR | Kansas City Southern Railway Company |
| SR | Southrail Corp. (Kansas City Southern Railway) |
| SRAX | Southern Rail Associates |
| SRBU | Leidos |
| SRC | Strasburg Rail Road |