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Right- and left-hand traffic
Right-hand traffic and left-hand traffic mean regulations requiring all traffic to keep either to the left or the right hand side of the road. This is so fundamental to traffic flow that it is sometimes referred to as the rule of the road. This basic rule eases traffic flow and reduces the risk of head-on collisions. Though originally most traffic drove on the left worldwide, today about 66% of the world's people live in right-hand traffic countries and 34% in left-hand traffic countries. About 72% of the world's total road distance carries traffic on the right, and 28% on the left.
Changing to right-hand traffic
Over the course (過程;進程) of the 20th century, there was a gradual worldwide shift from driving on the left to the right. Portugal ([ˈportʃugḷ]) changed to right-hand traffic in 1928, and the parts of Canada which were still driving on the left changed over by 1923. The remainder of Italy changed over in the 1920s after Benito Mussolini (墨索里尼) came to power; Austria (奧地利) and Czechoslovakia ([ˌtʃɛkəsloˈvɑkɪə] 捷克斯拉夫) changed when Germany annexed ([əˈnɛks] 併吞,強佔;合併) or occupied them in late 1930s, and Hungary ([ˈhʌŋgərɪ] 匈牙利) followed suit (跟著做). In Austria the build-up of new traffic lights and rebuilding of tram (有軌電車) tracks was started before the annexation. The Latin American countries of Panama (巴拿馬) and Argentina ([ˌɑrdʒənˈtinə] 阿根廷) changed in 1943 and 1945 respectively, and the Philippines and China followed suit in 1946. Belize ([bɛˈliz] 貝里斯(中美洲一國家)) changed to right-hand traffic in 1961. Sweden ([ˈswidṇ] 瑞典) changed in 1967 and Iceland did as well in 1968. Burma ([ˈbɝmə] ( Myanmar的舊稱)緬甸) changed, allegedly ([əˈlɛdʒɪdlɪ] 據宣稱) on the advice of a wizard, in 1970.
Taiwan drove on the left under Japanese rule, but changed to driving on the right in 1946 after the government of the Republic of China assumed (承擔;就任;取得) administration; the same happened in North and South Korea, another former Japanese colony. However, some trains in Taiwan and Seoul ([sol]) still keep to the left, as does pedestrian ([pəˈdɛstrɪən]) traffic in the Seoul subway system.
The most common reason for countries to switch to right-hand traffic is for conformity (相似;一致;符合) with neighbors, as it increases the safety of cross-border traffic. For example, several former British colonies in Africa, such as The Gambia (甘比亞(西非的獨立國)), Sierra Leone (獅子山(非洲西北部大西洋岸一國家)), Nigeria (奈及利亞), and Ghana ([ˈgɑnə]迦納(西非國家)), have changed from driving on the left to the right, because they all share borders with former French colonies, which drive on the right. The former Portuguese ([ˈportʃuˌgiz]) colony of Mozambique ([ˌmozəmˈbik]莫三比克) continues to drive on the left, which is a legacy of its Portuguese past; even though Portugal itself changed over in the 1920s, Mozambique continues to drive on the left because all its bordering countries do. Decisions by countries to drive on the right typically center on regional uniformity. There are historical exceptions, such as postilion ([poˈstɪljən] 左馬御者) riders in France, but such historical advantages do not apply to modern road vehicles.
There is a popular story that Napoleon changed the rule of the road in the countries he conquered from keep-left to keep-right. The justifications (正當的理由;藉口) mentioned are usually symbolic, such as that Napoleon himself was left- (or right-) handed, or that Britain, Napoleon's enemy, kept left. This story has never been shown to have a factual basis and it appears to be a legend.
Foreign occupation and military transit
Many countries have temporarily or permanently changed their rule of the road as a result of foreign occupation. Recent examples include Austria, Czechoslovakia (details) and Hungary under German rule or military transit in the 1930s and 1940s. The Channel Islands (英屬海峽群島) also changed to driving on the right under German occupation, but changed back after liberation in 1945. The Falkland Islands (福克蘭群島) did the same under Argentine control during the 1982 Falklands War, although some islanders refused to observe (遵守,奉行) the new rule and continued to drive on the left. East Timor (東帝汶) changed to driving on the left under Indonesian ([ˌɪndəˈniʃən]) rule in 1976, and continues the practice as an independent state. The Japanese region of Okinawa changed from left to right under US control; in 1972 Okinawa was returned to Japanese sovereignty ([ˈsɑvrɪntɪ]), and six years later, in 1978, the driving rules reverted to left-hand traffic as in mainland Japan.
Safety factors
Research in 1969 by J. J. Leeming showed countries driving on the left have a lower collision rate than countries driving on the right. It has been suggested this is partly because humans are more commonly right-eye dominant than left-eye dominant. In left-hand traffic, the predominantly better-performing right eye is used to monitor oncoming traffic and the driver's wing mirror. In right-hand traffic, oncoming traffic and the driver's wing mirror are handled by the predominantly weaker left eye. Some countries that have switched to driving on the right, such as Sweden, have seen their collision rates increase out of proportion to the increase in traffic volume.
History
In 1998, archaeologists ([ˌɑrkɪˈɑlədʒɪst] 考古學家) found a well-preserved track leading to a Roman quarry ([ˈkwɔrɪ] (採)石場;露天礦場) near Swindon, England. The grooves ([gruv] 溝;槽;(車)轍;(唱片)紋(道)) in the road on the right side were observed to be much deeper than those on the left side, which would make sense given that carts would be driven without any load on the way to the quarry, but would return laden with stone. These grooves suggest that the Romans drove on the left, at least in this particular location.
In fact, some, for example C. Northcote Parkinson, believed that ancient travelers on horseback generally rode on the left side of the road. As more people are right-handed, horsemen would thus be able to hold the reins ([ren]韁繩) with their left hands and keep their right hand free—to offer in friendship to passing riders or to defend themselves with swords, if necessary. It is often suggested this practice was brought about by the use of Postilions on coaches ((舊時的)四輪大馬車,公共馬車), in some countries they sat facing forward, in others back.
The first legal reference in Britain to an order for traffic to remain on the left occurred in 1756 with regard to London Bridge. The Highway Act 1773 contained a recommendation that horse traffic should remain on the left and this is enshrined ([ɪnˈʃrａɪn] 把...置於神龕內; 珍藏;銘記) in the Highway Act 1835.
In the late 1700s, the shift from left to right that took place in countries such as the United States was based on teamsters' ((一組騾、牛、馬等的)駕馭者; 美】運貨卡車駕駛員) use of large freight ([fret] 貨運(通常與快遞express相對)) wagons ([ˈwægən](四輪)運貨馬車) pulled by several pairs of horses. The wagons had no driver’s seat, so a postilion sat on the left rear horse and held his whip in his right hand. Seated on the left, the driver preferred that other wagons pass him on the left so that he could be sure to keep clear of the wheels of oncoming wagons. He did that by driving on the right side of the road.
Countries that became part of the British Empire adopted the British keep-left rule, although many have since changed. In Canada, the Maritime ([ˈmærəˌtａɪm]) provinces and British Columbia initially drove on the left, but changed to the right in order to make border crossings to and from the United States easier. Nova Scotia ([ˈskoʃə] Nova Scotia: 新斯科細亞省(加拿大省名)) switched to driving on the right on April 15, 1923.