The most important rule of the road concerns which side to drive on. A large proportion of accidents in the world happen for this reason, with more and more people choosing car hire as the way to navigate a foreign country. Famously actor Matthew Broderick was involved in a bad collision when renting a car in Ireland because he forgot that they drive on the opposite side of the road.
Most areas of the world which were formerly British colonies still drive on the left hand side of the road including Australia, the Caribbean, India and South Africa. Japan also drives on the left. Europe generally drives on the right hand side apart from Cyprus, Ireland, Malta and the United Kingdom. Guyana and Suriname are the only countries in South America to drive on the left. If you plan to rent a car in the UK
or any other country that drives on the left and you usually drive on the right, you should take extreme care for the first few miles until comfortable with driving on the other side fo the road.
About two thirds of the countries in the world drive on the right including the USA, China and Russia. Canada used to drive on the left but changed to the right to make border crossings with the United States of America more manageable.
The reasons for driving on different sides of the road are historical. British horse riders used to ride on the left hand side of the road, thus keeping their right arm free to offer greetings to passersby or draw their sword. But in the USA Teamsters (who drove animals) used to sit on the left hand horse while driving a wagon and therefore keep their right hand free for whipping the other horses. In order to avoid collisions they decided to start driving on the right so that they could see the passing wheels of other wagons.
Some of the other major countries not previously mentioned which drive on the left are the Bahamas, Bangladesh, the Cook Islands, the Falkland Islands, Hong Kong, Indonesia, Kenya, Malaysia, New Zealand, Sri Lanka, Thailand and Zimbabwe. See the table and image below for a full list of countries that drive on the left or our full size map here