Left- and right-hand traffic

Left-hand traffic and right-hand traffic are the practices, in bidirectional traffic, of keeping to the left side or to the right side of the road, respectively. They are fundamental to traffic flow, and are sometimes called a "rule of the road". The terms right- and left-hand "drive" refer to the position of the driver and the steering wheel in the vehicle and are, in automobiles, the reverse of the terms right- and left-hand "traffic". The rule also includes where on the road a vehicle is to be driven, if there is room for more than one vehicle in one direction, and the side on which the vehicle in the rear overtakes the one in the front. For example, a driver in an LHT country would typically overtake on the right of the vehicle being overtaken.
RHT is used in 165 countries and territories, mainly in the Americas, Continental Europe, most of Africa and mainland Asia, while 75 countries use LHT, which account for about a sixth of the world's land area, a quarter of its roads, and about a third of its population. In 1919, 104 of the world's territories were LHT and an equal number were RHT. Between 1919 and 1986, 34 of the LHT territories switched to RHT.
While many of the countries using LHT were part of the British Empire, others such as Indonesia, Japan, Nepal, Bhutan, Macau, Thailand, Mozambique and Suriname were not. Sweden and Iceland, which have used RHT since September 1967 and late May 1968 respectively, previously used LHT. All of the countries that were part of the French Colonial Empire adopted RHT.
Historical switches of traffic handedness have often been motivated by factors such as changes in political administration, a desire for uniformity within a country or with neighboring states, or availability and affordability of vehicles.
In LHT, traffic keeps left and cars usually have the steering wheel on the right and roundabouts circulate clockwise. RHT is the opposite: traffic keeps right, the driver usually sits on the left side of the car, and roundabouts circulate counterclockwise.
In most countries, rail traffic follows the handedness of the roads; but many of the countries that switched road traffic from LHT to RHT did not switch their trains. Boat traffic on bodies of water is RHT, regardless of location. Boats are traditionally piloted from the starboard side to facilitate priority to the right.

Background

Historically, many places kept left, while many others kept right, often within the same country. There are many myths that attempt to explain why one or the other is preferred. About 90 percent of people are right-handed, and many explanations reference this. Horses are traditionally mounted from the left, and led from the left, with the reins in the right hand. So people walking horses might use RHT, to keep the animals separated. Also referenced is the need for pedestrians to keep their swords in the right hand and pass on the left as in LHT, for self-defence. It has been suggested that wagon-drivers whipped their horses with their right hand, and thus sat on the left-hand side of the wagon, as in RHT. Academic Chris McManus notes that writers have stated that in 1300, Pope Boniface VIII directed pilgrims to keep left; others suggest that he directed them to keep to the right, and there is no documented evidence to back either claim.

Geographical areas

Africa

The British Empire introduced LHT in the East Africa Protectorate, the Protectorate of Uganda, Tanganyika, Rhodesia, Eswatini and the Cape Colony, as well as in British West Africa ; former British West Africa, however, has now switched to RHT, as all its neighbours, which are mostly former French territories, use RHT. South Africa, formerly the Cape Colony, introduced LHT in former German South West Africa, present-day Namibia, after the end of World War I.
Sudan, formerly part of Anglo-Egyptian Sudan, switched to RHT in 1973. Most of its neighbours were RHT countries, with the exception of Uganda and Kenya, but since the independence of South Sudan in 2011, all of its neighbours drive on the right.
Although Portugal switched to RHT in 1928, its colony of Mozambique remained LHT because it has land borders with former British colonies.
France introduced RHT in French West Africa and the Maghreb, where it is still used. Countries in these areas include Mali, Mauritania, Ivory Coast, Burkina Faso, Benin, Niger, Morocco, Algeria, and Tunisia. Other French former colonies that are RHT include Cameroon, Central African Republic, Chad, Djibouti, Gabon, and the Republic of the Congo.
Rwanda and Burundi are RHT but are considering switching to LHT.

Americas

United States

In the late 18th century, right-hand traffic started to be introduced in the United States based on teamsters' use of large freight wagons pulled by several pairs of horses and without a driver's seat; the postilion held his whip in his right hand and thus sat on the left rear horse, and therefore preferred other wagons passing on the left so that he would have a clear view of other vehicles. The first keep-right law for driving in the United States was passed in 1792 and applied to the Philadelphia and Lancaster Turnpike. Massachusetts formalized RHT in 1821. However, the National Road was LHT until 1850, "long after the rest of the country had settled on the keep-right convention". Today the United States is RHT except the United States Virgin Islands, which is LHT like many neighbouring islands.
Some special-purpose vehicles in the United States, like certain postal service trucks, garbage trucks, and parking-enforcement vehicles, are built with the driver's seat on the right for safer and easier access to the curb. A common example is the Grumman LLV, which is used nationwide by the US Postal Service and by Canada Post.

Other countries in the Americas

In Canada, the provinces of Quebec and Ontario were always RHT because they were created out of the former French colony of New France. The province of British Columbia changed to RHT in stages from 1920 to 1923, New Brunswick, Nova Scotia, and Prince Edward Island in 1922, 1923, and 1924 respectively, and the Dominion of Newfoundland in 1947.
In the West Indies, colonies and territories drive on the same side as their parent countries, except for the United States Virgin Islands. Many of the island nations are former British colonies and drive on the left, including Jamaica, Antigua and Barbuda, Barbados, Dominica, Grenada, Saint Kitts and Nevis, Saint Lucia, Saint Vincent and the Grenadines, Trinidad and Tobago, and The Bahamas. However, most vehicles in The Bahamas, Cayman Islands, Turks and Caicos Islands and both the British Virgin Islands, and the United States Virgin Islands are LHD due to their being imported from the United States.
Brazil, a Portuguese colony until the early 19th century, had in the 19th and the early 20th century mixed rules, with some regions still on LHT, switching these remaining regions to RHT in 1928, the same year Portugal switched sides. Other Central and South American countries that later switched from LHT to RHT include Argentina, Panama, Paraguay, and Uruguay.
Suriname and its neighbour Guyana are the only two remaining LHT countries in South America.

Asia

LHT was introduced by the UK in British India, British Malaya and British Borneo, as well as British Hong Kong. These countries, except Myanmar, are still LHT, as well as neighbouring countries Bhutan and Nepal. Myanmar switched to RHT in 1970, although much of its infrastructure is still geared to LHT as its neighbours India, Bangladesh and Thailand use LHT. Most cars are used RHD vehicles imported from Japan. Afghanistan was LHT until the 1950s, in line with Pakistan.
Although Portuguese Timor, which shares the island of Timor with Indonesia, who is LHT, switched to RHT with Portugal in 1928, it switched back to LHT in 1976 during the Indonesian occupation of East Timor.
In the 1930s, parts of China such as the Shanghai International Settlement, Canton and Japanese-occupied northeast China used LHT. However, in 1946 the Republic of China made RHT mandatory in China. Taiwan was LHT under Japanese colonization from 1895–1945. Portuguese Macau remained LHT, along with British Hong Kong, despite being transferred to China in 1999 and 1997 respectively.
Both North Korea and South Korea use RHT since 1946, after liberation from Japanese colonialization.
The Philippines was mostly LHT during its Spanish and American colonial periods, as well as during the Commonwealth era. During the Japanese occupation, the Philippines remained LHT, as was required by the Japanese; but during the Battle of Manila, the liberating American forces drove their tanks to the right for easier facilitation of movement. RHT was formalized in 1945 through a decree by president Sergio Osmeña. Even though RHT was formalized, RHD vehicles such as public buses were still imported into the Philippines until a law passed banning the importation of RHD vehicles except in special cases. These RHD vehicles are required to be converted to LHD.
Japan was never part of the British Empire, but its traffic also drives on the left. Although this practice goes back to the Edo period, it was not until 1872 – the year Japan's first railway was introduced, built with technical aid from the British – that this unwritten rule received official acknowledgment. Gradually, a massive network of railways and tram tracks was built, with all railway vehicles driven on the left-hand side. However, it took another half-century, until 1924, until left-hand traffic was legally mandated. Post-World War II Okinawa was ruled by the United States Civil Administration of the Ryukyu Islands until 1972, and was RHT until 6 a.m. the morning of 30 July 1978, when it switched back to LHT. The conversion operation was known as 730. Okinawa is one of only a few places to have changed from RHT to LHT in the late 20th century. While Japan drives on the left and most Japanese vehicles are RHD, imported vehicles are generally bought as LHD since LHD cars are considered to be status symbols.
Vietnam became RHT as part of French Indochina, as did Laos and Cambodia. In Cambodia, RHD cars, many of which were smuggled from Thailand, were banned in 2001, even though they accounted for 80% of vehicles in the country.