49 CFR 213.309 - Restoration or renewal of track under traffic conditions.
(a) Restoration or renewal of track under traffic conditions is limited to the replacement of worn, broken, or missing components or fastenings that do not affect the safe passage of trains.
(b) The following activities are expressly prohibited under traffic conditions:
(1) Any work that interrupts rail continuity, e.g., as in joint bar replacement or rail replacement;
(2) Any work that adversely affects the lateral or vertical stability of the track with the exception of spot tamping an isolated condition where not more than 15 lineal feet of track are involved at any one time and the ambient air temperature is not above 95 degrees Fahrenheit; and
(3) Removal and replacement of the rail fastenings on more than one tie at a time within 15 feet.