Specifications
The Vienna Convention on Road Signs and Signals 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. The white uppercase letters forming the stop legend are 25 cm tall. Larger signs of 90 cm (36 in) with 30 cm (12 in) legend and 25 mm (⅞ in) border are used on multilane expressways. Regulatory provisions exist for extra-large 120 cm (48 in) signs with 40 cm (16 in) legend and 30 mm (1¼ in) border for use where sign visibility or reaction distance are limited, and the smallest permissible stop sign size for general usage is 60 cm (24 in) with a 20 cm (8 in) legend and 15 mm (⅝ in) border. The metric units specified in the US regulatory manuals are rounded approximations of English units, not exact conversions. Field, legend, and border are all retroreflective.
The stop instruction is specified with either an English stop or local language legend in the United Nations Convention on Road Signs and Signals. Some countries use both. The sign's distinctive design was developed and first used in the U.S., and later adopted by other countries and by the U.N. Despite this, the U.S. is not a signatory to the U.N. Traffic Signs and Signals Convention.
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