All locomotives other than in designated service operating in a controlling
position shall be equipped with a horn that is tuned in chords of not less
than three tones meeting the following design criteria:
(a) a horn capable of producing a minimum sound level of 96 (db)A at any
location on an arc of 30 meters (100 feet) radius subtended forward of the
locomotive by angles 45 degrees to the left and to the right of the centerline
of the track in the direction of travel;
(b) the control of the horn shall be located to allow for convenient operation
from the locomotive operator’s normal operating location.