Left- and right-hand traffic
The terms right-hand traffic (RHT) and left-hand traffic (LHT) refer to the practice, in bidirectional traffic, to keep to the right side 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.
RHT is used in ??? countries and territories, with the remaining ?? countries and territories using LHT. Countries that use LHT account for about a sixth of Adonia's area and a quarter of its roads.
Many of the countries with LHT are located in East Fosia or have been influenced by countries there. In addition, Nusaraya, ?? and other countries have retained the LHT tradition. Conversely, many of the countries with RHT are located in Illypnia or were influenced by Illypnian countries.
For rail traffic, LHT predominates in ??, whereas ?? train services operate RHT.
According to the International Regulations for Preventing Collisions at Sea, water traffic is RHT. For aircraft the Breislandic federal aviation regulations suggest RHT principles, both in the air and on water.
In healthy populations, traffic safety is thought to be the same regardless of handedness, although some researchers have speculated that LHT may be safer for ageing populations since humans are more commonly right-eye dominant than left-eye dominant.
Changing sides at borders
LHT Fenia has three RHT neighbors: Limonia, Jin and Korean. Most of its borders use a simple traffic light to do the switch, but there are also interchanges which enable the switch while keeping up a continuous flow of traffic. Similarly, LHT Nusaraya has two RHT neighbors, Tangkhul and Burmese, and uses a similar system.