49 CFR § 232.205
Each train and each car in the train shall receive a Class I brake test as described in paragraph (c) of this section by a qualified person, as defined in 232.5, at the following points:
(1) The location where the train is originally assembled (“initial terminal”);
(2) A location where the train consist is changed other than by:
(i) Adding a single car or a solid block of cars, except as provided in paragraph (b)(2) of this section;
(ii) Removing a single car or a solid block of cars;
(iii) Removing cars determined to be defective under this chapter; or
(iv) A combination of the changes listed in paragraphs (a)(2)(i) through (a)(2)(iii) of this section (See §§ 232.209 and 232.211 for requirements related to the pick-up of cars and solid blocks of cars en route.);
(3) A location where the train is off-air for a period of more than 24 hours.
(4) A location where a unit or cycle train has traveled 3,000 miles since its last Class I brake test; and
(5) A location where the train is received in interchange if the train consist is changed other than by:
(i) Removing a car or a solid block of cars from the train;
(ii) Adding a previously tested car or a previously tested solid block of cars to the train;
(iii) Changing motive power;
(iv) Removing or changing the caboose; or
(v) Any combination of the changes listed in paragraphs (a)(5) of this section.
(A) If changes other than those contained in paragraph (a)(5)(i)-(a)(5)(v) of this section are made to the train consist when it is received in interchange and the train will move 20 miles or less, then the railroad may conduct a brake test pursuant to § 232.209 on those cars added to the train.