49 C.F.R. § 299.321 – Defective rails.

(a) The railroad's inspection, testing, and maintenance program shall include a description of defective rails consistent with the practice on the Tokaido Shinkansen system. The inspection, testing, and maintenance program shall include identification of rail defect types, definition of the inspection criteria, time required for verification and the corresponding remedial action.
(b) When the railroad learns that a rail in that track contains any of the defects listed in the railroad's inspection, testing, and maintenance program, a person designated under § 299.353 or § 299.355 shall determine whether the track may continue in use. If the designated person determines that the track may continue in use, operation over the defective rail is not permitted until—
1. (1) The rail is replaced or repaired; or
2. (2) The remedial action prescribed in the inspection, testing, and maintenance program is initiated.