| Abbreviation | Definition |
|---|---|
| MKIX | M-K Railroad Equipment Leasing (Morrison Knudsen Corporation) |
| MKIX | Morrison Knudsen Corporation |
| MKNR | Mackenzie Northern Railway |
| MKT | Missouri-Kansas-Texas Railroad (Union Pacific Railroad) |
| MKT | Union Pacific Railroad Company |
| MKTT | Missouri-Kansas-Texas Railroad (Union Pacific Railroad) |
| MKTT | Union Pacific Railroad Company |
| MKTZ | Missouri Pacific Railroad |
| MKTZ | Missouri-Kansas-Texas Railroad (Union Pacific Railroad) |
| MLCG | Main Line Canal GeoTrail |
| MLCU | N. Y. K. Line |
| MLCU | N.Y.K. Line |
| MLCX | American Refrigerator Transit |
| MLCX | American Refrigerator Transit Company |
| MLD | Midland Railway Co. of Manitoba |
| MLDR | Multi Limit Dog Rail |
| MLEX | Miles Inc. |
| MLEX | Miles Incorporated |
| MLHU | Matson Incorporated |
| MLHX | American Refrigerator Transit |