The whistle must be sounded where required by rule or law. In case of whistle failure, speed of train must be reduced and the bell rung continuously when approaching and passing through stations, yards, over public crossings, and around curves.
The signals prescribed are illustrated by "o" for short sounds; "—" for longer sounds. The sound of the whistle should be distinct, with intensity and duration proportionate to the distance signal is conveyed.
The unnecessary use of the whistle is prohibited and it must not be sounded while passing or being passed by a passenger train, except where required by rule or law, or in case of an emergency.