| Abbreviation | Definition |
|---|---|
| MR | Midland Railway |
| MRAC | Mounted Rail Attachment Clamp |
| MRAD | Radiance City, North Red (Railway station code) |
| MRAX | Mineral Range |
| MRB | Martinsburg Station (MARC - AMTK) |
| MRCX | Evans Railcar Leasing (GE Rail Services Corporation) |
| MRCX | General Electric Railcar Services Corporation |
| MRDX | MidAmerican Energy |
| MREX | Marshall Railway Equipment Corporation (Monad Railway Equipment) |
| MREX | Monad Railway Equipment Company |
| MRFC | Metropolitan Rail Freight Council |
| MRFS | Modular Rail Forend System |
| MRHS | Midland Railway |
| MRI | Mohall Railroad |
| MRIX | Motive Rail Industries |
| MRL | Montana Rail Link |
| MRL | Montana RailLink Incorporated |
| MRLX | Mid America Railcar Leasing |
| MRM | Monticello Railway Museum |
| MRMX | MRMX Leasing and Management |