<P> The terms left - hand traffic (LHT) and right - hand traffic (RHT) refer to regulations requiring all bidirectional traffic, unless otherwise directed, to keep to the right or to the left side of the road, respectively . This is so fundamental to traffic flow that it is sometimes referred to as the rule of the road . </P> <P> One hundred and sixty - three countries and territories use RHT, with the remaining seventy - six countries and territories using LHT . Countries that use LHT account for about a sixth of the world's area and a quarter of its roads . In the early 1900s some countries including Canada, Spain, and Brazil had different rules in different parts of the country . During the 1900s many countries standardised within their jurisdictions, and changed from LHT to RHT, mostly to conform with regional custom . In 1919, 104 of the world's territories were LHT and an equal number were RHT . From 1919 to 1986, 34 of the LHT territories switched to RHT . </P> <P> Many of the countries with LHT are former British colonies in the Caribbean, Southern Africa, Southeast Asia, South Asia, Australia, and New Zealand . Japan, Thailand, Nepal, Bhutan, Mozambique, Suriname, East Timor, and Indonesia are among those LHT countries outside the former British Empire . In Europe, only four countries still drive on the left: the United Kingdom, Ireland, Malta, and Cyprus, all of which are on islands that have no direct road connections with countries driving on the right . </P> <P> Nearly all countries use one side or the other throughout their entire territory . Most exceptions are due to historical considerations and / or involve islands with no road connection to the main part of a country . China is RHT except the Special Administrative Regions of China of Hong Kong and Macau . The United States is RHT except the United States Virgin Islands . The United Kingdom is LHT, but its overseas territories of Gibraltar and British Indian Ocean Territory are RHT . </P>

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