countries by handedness of road traffic, c. 2019
left-hand traffic (lht) and right-hand traffic (rht) are the practice, in bidirectional traffic, of keeping to the left side or to the right side of the road, respectively. a fundamental element to traffic flow, it is sometimes referred to as the rule of the road.
rht is used in 165 countries and territories, with the remaining 75 countries and territories using lht. countries that use lht account for about a sixth of the world's area with about a third of its population and a quarter of its roads. 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.
many lht countries were formerly part of the british empire, although some were not, such as japan, thailand, indonesia, and suriname. conversely, many rht countries were part of the french colonial empire.
in lht vehicles keep left, and cars are rhd (right-hand drive) with the steering wheel on the right-hand side and the driver sitting on the offside or side closest to the centre of the road. the passenger sits on the nearside, closest to the curb. roundabouts circulate clockwise. in rht everything is reversed: cars keep right, the driver sits on the left side of the car, and roundabouts circulate counterclockwise.
in most countries rail traffic follows the handedness of the roads, although many of the countries that switched road traffic from lht to rht did not switch their trains. boat traffic on rivers is effectively rht. boats are traditionally piloted from the starboard side to facilitate priority to the right.