(a) Manually-operated horns or other audible warning devices provided on self-propelled mobile equipment as a safety feature shall be maintained in functional condition.

(b)   (1) When the operator has an obstructed view to the rear, self-propelled mobile equipment shall have —   (i) An automatic reverse-activated signal alarm;   (ii) A wheel-mounted bell alarm which sounds at least once for each three feet of reverse movement;   (iii) A discriminating backup alarm that covers the area of obstructed view; or   (iv) An observer to signal when it is safe to back up.   (2) Alarms shall be audible above the surrounding noise level.   (3) An automatic reverse-activated strobe light may be used at night in lieu of an audible reverse alarm.

(c) This standard does not apply to rail equipment.