About a quarter of the world drives on the left, and the countries that do are mostly old British colonies. This strange quirk perplexes the rest of the world; however, there is a perfectly good reason. Up to the late 1700's, everybody travelled on the left side of the road because it's the sensible option for feudal, violent societies of mostly right-handed people. Jousting knights with their lances under their right arm naturally passed on each other's right, and if you passed a stranger on the road you walked on the left to ensure that your protective sword arm was between yourself and him. Revolutionary France, however, overturned this practice as part of its sweeping social rethink. A change was carried out all over continental Europe by Napoleon.The reason it changed under Napoleon was because he was left handed his armies had to march on the right so he could keep his sword arm between him and any opponent. From then on, any part of the world which was at some time part of the British Empire was thus left hand and any part colonised by the French was right hand. In America, the French colonised the southern states (Louisiana for instance) and the Canadian east coast (Quebec). The Dutch colonised New York (or New Amsterdam). The Spanish and Portugese colonised the southern Americas. So The British were a minority in shaping the 'traffic'. The drive-on-the-right policy was adopted by the USA, which was anxious to cast off all remaining links with its British colonial past. Once America drove on the right, left-side driving was ultimately doomed. If you wanted a good reliable vehicle, you bought American, for a period they only manufactured right-hand-drive cars. From then on many countries changed out of necessity. Today, the EC would like Britain to fall into line with the rest of Europe, but this is no longer possible. It would cost billions of pounds to change everything round. The last European country to convert to driving on the right was Sweden in 1967. While everyone was getting used to the new system, they paid more attention and took more care, resulting in a reduction of the number of road accident casualties.

I can't disagree with willie, but I heard a different angle that may factor in. Left-side-drive traffic is found is cultures wherein many people carried swords secured by a belt at the left hip. When you met someone in the street, you did not want your sword or scabbard to strike the person (especially if un-armed) nor your weapons to clash, which could precipitate hostility, you met and passed on your left, his right to keep your weapons away from him so you did not cause an incident. Japanese and British carried swords in this fashion and developed these traffic habits as did the cultures where their influence was important, especially during sword-carrying times.

The road is supposed to have been invented by the Romans, who marched on the left.. This carried on through the ages.. The switch to driving on the right can also be put down to two main occurences.. Napoleon refusing to have his troops etc. march on the same side of the road as the British, and then later because of the American War of Independence, the US authourities decided their countrymen would ride / drive on the opposite side to the British aswell.

Its the law, plus it always proves dangerous to drive against traffic. :-) In all seriousness it was first more prudent for people to have a weapon on the inside when travelling. Then the french decided they wanted to be on the other side of the road to be different.

law requirement

Your closer to the center of the road, so you can judge distance easier from moving cars over the other side. Also it gives the illusion of control.