Train, for purposes of subparts A and B of this part, means one or more locomotives coupled with or without cars, requiring an air brake test in accordance with 49 CFR part 232 or part 238, except during switching operations or where the operation is that of classifying and assembling rail cars within a railroad yard for the purpose of making or breaking up trains. The term, for purposes of subpart C of this part, means -
(1) A single locomotive,
(2) Multiple locomotives coupled together, or
(3) One or more locomotives coupled with one or more cars.
49 CFR § 220.5
As used in this part, the term: