Stop sign
Overview
 
A Stop sign is a traffic sign
Traffic sign
Traffic signs or road signs are signs erected at the side of roads to provide information to road users. With traffic volumes increasing over the last eight decades, many countries have adopted pictorial signs or otherwise simplified and standardized their signs to facilitate international travel...

 to notify drivers that they must stop before proceeding.
The Vienna Convention on Road Signs and Signals
Vienna Convention on Road Signs and Signals
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 signing system for road traffic in use internationally.This convention was agreed upon by the United Nations Economic and Social...

 proposed standard stop sign diameters of 0.6, 0.9 or 1.2 metres. UK and New Zealand stop signs are 750, 900 or 1200 mm, according to sign location and traffic speeds. In the United States, stop signs have a size of 75 cm across opposite flats of the red octagon, with a 20mm white border.
 
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