Article 28. Audible and Luminous Warnings

1. Audible warning devices may be used only:
    (a) To give due warning with a view to avoiding an accident;
    (b) Outside built-up areas when it is desirable to warn a driver that he is about to be overtaken. The sounds emitted by audible warning devices shall not be prolonged more than necessary.

2. Motor-vehicle drivers may give the luminous warnings specified in Article 32, paragraph 3, of this Convention, instead of audible warnings, between nightfall and dawn. They may also do so in daylight hours for the purpose indicated in paragraph 1 (b) of this Article, if to do so is more appropriate in the prevailing circumstances.

3. Contracting Parties or subdivisions thereof may authorize the use of luminous warnings in built-up areas also for the purpose referred to in paragraph 1 (b) of this Article.