(a) Rail trailer-on-flatcar/container-on-flatcar (TOFC/COFC) service means the transportation by rail, in interstate or foreign commerce, of—

(1) Any freight-laden highway truck, trailer, or semitrailer,

(2) The freight-laden container portion of any highway truck, trailer, or semitrailer having a demountable chassis,

(3) Any freight-laden multimodal vehicle designed to operate both as a highway truck, trailer, or semitrailer and as a rail car,

(4) Any freight-laden intermodal container comparable in dimensions to a highway truck, trailer, or semitrailer and designed to be transported by more than one mode of transportation, or

(5) Any of the foregoing types of equipment when empty and being transported incidental to its previous or subsequent use in TOFC/COFC service.

(b) Highway TOFC/COFC service means the highway transportation, in interstate or foreign commerce, of any of the types of equipment listed in paragraph (a) of this section as part of a continuous intermodal movement that includes rail TOFC/COFC service, and during which the trailer or container is not unloaded.