49 CFR 233.5: Accidents resulting from signal failure.

Each carrier shall report within 24 hours to the Federal Railroad Administration by toll free telephone, number 800-424-0201, whenever it learns of the occurrence of an accident/incident arising from the failure of an appliance, device, method or system to function or indicate as required by part 236 of this title that results in a more favorable aspect than intended or other condition hazardous to the movement of a train.