49 CFR 299.433: Exterior lights.

(a) Headlights. Each leading end of a trainset shall be equipped with two or more headlights.

(1) Each headlight shall produce 80,000 candela.

(2) Headlights shall be arranged to illuminate signs in the right-of-way.

(3) Headlights shall be recognized 600 m (1,968 feet) ahead of the cab car by a driver in another trainset or a maintenance person standing in the right-of-way under clear weather conditions.

(b) Taillights (marking devices). (1) The trailing end of the trainset shall be equipped with two red taillights;

(2) Each taillight shall be located at least 1.2 m (3.9 feet) above rail;

(3) Each taillight shall be recognizable 200 m (656 feet) ahead of the cab car by a driver in another trainset or a maintenance person standing in the right-of-way under clear weather conditions;

(4) Taillights of the trailing end of the trainset shall be on when the trainset is in operation;

(5) Taillights shall not be on in the direction of trainset travel, except if the driver shall re-position the trainset in a station. Such re-positioning operations shall be done in accordance with the railroad's operating rules; and

(6) In an emergency situation, the headlight on the rear of the trainset may serve as the taillights in accordance with the railroad's operating rules.