| Abbreviation | Definition |
|---|---|
| MELX | Sunbelt Cement Incorporated |
| MEM | Memphis Amtrak Station |
| MEPX | McGraw-Edison |
| MEPX | McGraw-Edison Company |
| MERR | Maine Eastern Railroad |
| MERX | Merco |
| MERX | Merco A Joint Venture |
| MESX | Mears/ CPG Incorporated |
| MESX | Mears/CPG |
| MET | Metropark Station (NJTransit - AMTK) |
| MET | Modesto and Empire Traction |
| MET | Modesto and Empire Traction Company |
| METW | Municipality of East Troy Wisconsin |
| METX | Northeast Illinois Regional Commuter Railroad Corporation |
| METX | Northeast Illinois Regional Commuter Railroad Corporation (Metra) |
| MF | Middle Fork Railroad |
| MFCX | Farmers Coop Grain and Supply (First Union Rail) |
| MFCX | First Union Rail |
| MFFX | M4 Holdings |
| MFFX | M4 Holdings Limited |