| Abbreviation | Definition |
|---|---|
| POLX | PolyOne |
| POLZ | Polish Ocean Lines |
| POTB | Port of Tillamook Bay Railroad |
| POTX | General American Marks (GATX Corporation) |
| POTX | General American Marks Company |
| POV | Pittsburgh and Ohio Valley Railway |
| POVA | Pend Oreille Valley Railroad |
| POWX | Power Silicates Incorporated |
| POWX | Vinings Industries |
| PP | Project Proposal |
| PPAX | PCS Phosphate |
| PPCX | American Association of Private Railroad Car Owners (AAPRCO) |
| PPD | Pre Paid Destinations |
| PPGU | Axiall Corporation |
| PPGX | PPG Industries |
| PPGX | PPG Industries Incorporated |
| PPHX | PCS Phosphate |
| PPHX | PCS Phosphate Company |
| PPLX | Pennsylvania Power and Light |
| PPLX | Pennsylvania Power and Light Company |