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The Vienna Convention on Road Signs and Signals is an international treaty designed to increase road safety and aid international road traffic by standardising the road signs, traffic lights and road markings in use internationally. This convention was agreed upon by the United Nations Economic and Social Council at the UNESC Conference on Road Traffic in Vienna 7 October 1968 to 8 November 1968, and came into force 6 June 1978. This conference also produced the Vienna Convention on Road Traffic, which complements this legislation by standardising international traffic laws.
The convention classes all road signs into a number of categories and subcategories:
The convention then lays out precise colours, sizes and shapes for each of these classes of sign:
† May be written in English or the national language
It also specifies the symbols and pictograms which may be used, and the orientations in which they may be used. When more than one is available, the same one must be used nationally. All signs, except for those which do not apply at night, must be reflective enough to been seen in darkness with headlights from a distance.
The convention also specifies road markings. All such markings must be less than 6 mm high, with cat's eye reflectors no more than 15 mm above the road surface.
The length and width of markings varies according to purpose, although no exact figures for size are stated; roads in built up areas should use a broken line for lane division, while continuous lines must only be used in special cases, such as reduced visibility or narrowed carriage ways.
All words painted on the road surface should be either of place names, or of words which are recognisable in most languages, such as "Stop" or "Taxi".
The Convention specifies the colours which may be used for traffic lights and their meanings, and places and purposes for which lights may be used, like so:
Red flashing lights may only be used at the locations specified above; any other use of the lights is in breach of the convention. Red lights must be placed on top when lights are stacked vertically, or on the side closest to oncoming traffic if stacked horizontally.