| 1 | TTHX | Trailer Train Co. | added 10/1966; 10/1966-1/1980; eliminated 1/1992 | | NAKINA |
| 2 | TTHX | TTX Co. | added 1/1992; 1/1994-7/2005 | | NAKINA |
| 3 | TTHX | Trailer Train Co. (heavy duty chain equipped cars) | added 10/1966; 10/1966 | | NAKINA |
| 4 | TTHX | Trailer Train Co. (FMS flats specifically equipped with heavy duty chains anchored to removable stake pocket castings — when tiedowns are removed car becomes same as MTTX) | 10/1968 | | NAKINA |
| 5 | TTHX | Trailer Train Co. (flat cars, equipped with heavy duty chains anchored to removable stake pocket castings. When tie-downs are removed, car becomes same as 60' car stencilled ""MTTX"") | 4/1970-1/1980 | | NAKINA |
| 6 | TTHX | Trailer Train Co./TTX Co. (flat cars equipped with 18 heavy-duty chains anchored to removable stake pocket castings. When tie-downs are removed, car becomes same as 60' flat cars stencilled MTTX) | 7/1985-7/2000 | | NAKINA |
| 7 | TTHX | Trailer Train Co. (heavy duty chain equipped cars) | added 10/66; 10/66 | | NRHS |
| 8 | TTHX | Trailer Train Co. (FMS flats specifically equipped with heavy duty chains anchored to removable stake pocket castings -- when tiedowns are removed car becomes same as MTTX) | Oct-68 | | NRHS |
| 9 | TTHX | Trailer Train Co. | Apr-70 | | NRHS |
| 10 | TTHX | Trailer Train Co. (flat cars, equipped with heavy duty chains anchored to removable stake pocket castings. When tie-downs are removed, car becomes same as 60' car stencilled "MTTX") | 1/75-1/80 | | NRHS |
| 11 | TTHX | Trailer Train Co. | eliminated 1/92 | | NRHS |
| 12 | TTHX | TTX Co. | added 1/92 | | NRHS |
| 13 | TTHX | TTX Co. (flat cars equipped with 18 heavy-duty chains anchored to removable stake pocket castings. When tie-downs are removed, car becomes same as 60' flat cars stencilled MTTX) | 1/94-7/2000 | | NRHS |
| 14 | TTHX | TTX COMPANY {TRAILER TRAIN COMPANY} | | | PWRC |
| 15 | TTHX | Trailer Train (TTX Corporation) | | | RSRV |
| 16 | TTHX | TTX COMPANY | | | SCAC4 |
