Kilometres Per Hour - Regulatory Use

Regulatory Use

During the early years of the motor car, each country developed its own system of road signs. In 1968 the Vienna Convention on Road Signs and Signals was drawn up under the auspices of the United Nations Economic and Social Councilto harmonise road signs across the world. Many countries have since signed the convention and adopted its proposals. Speed limits signs that are either directly authorised by the convention or have been influenced by the convention are shown below:

• 100 km/h sign following the most common implementation of the Vienna Convention style (Hungary)

• Swedish 30 km/h speed limit - the yellow background provides a contrast should the sign be covered by snow.

• Since the text "km/h" on this Irish speed limit sign is a symbol, not an abbreviation, it represents both "kilometres per hour" (English) and "ciliméadar san uair"(Irish)

• 60 km/h speed limit in Arabic and Latin scripts (UAE)

• Waterways speed limit of 9 km/h (Finland)

In 1972 the EU published a directive (overhauled in 1979 to take British and Irish interests into account) that required member states to abandon CGS-based units in favour of SI. The use of SI implicitly required that member states use "km/h" as the shorthand for "kilometres per hour" on official documents.

Another EU directive, published in 1975, regulates the layout of speedometers within the European Union, uses the text "km/h" in all languages. Many of the languages used in the EU do not include all three letters "k", "m" and "h" in the local translation of "kilometres per hour". Examples include:

• Dutch: "kilometer per uur" ("hour" is spelt "uur" - does not start with "h"),
• Portuguese: "quilómetro por hora" ("kilometre" is spelt "quilómetro" - does not start with "k")
• Greek: "χιλιόμετρα ανά ώρα" (a different script).

In 1988 the United States National Highway Traffic Safety Administration promulgated a rule stating that "MPH and/or km/h" were to be used in speedometer displays. On May 15, 2000 this was clarified to read "MPH, or MPH and km/h". However, the Federal Motor Vehicle Safety Standard number 101 ("Controls and Displays") allows "any combination of upper- and lowercase letters" to represent the units.