Why is there a right- and left-hand traffic

Some historians, such as C. Northcote Parkinson, believed that ancient travellers on horseback generally rode on the left side of the road. As more people are right-handed, a horseman would thus be able to hold the reins with his left hand and keep his right hand free—to offer in friendship to passing riders or to defend himself with a sword, if necessary.

There is a popular story that Napoleon changed the rule of the road in the countries he conquered from keep-left to keep-right. Some justifications are symbolic, such as that Napoleon himself was left- (or right-) handed, or that Britain, Napoleon's enemy, kept left. Alternatively, troops passing on the left may have been tempted to raise their right fists against each other. Forcing them to pass on the right reduced conflict. Hence, island nations such as Britain and Japan (using ships to move troops around and having less need to move them overland) continued to use the natural system. These stories have never been shown to have a factual basis and appear to be legends.^[18]

via en.wikipedia.org

Comments

[Joel O.]

I have heard these same stories! And here is one for you, the islands of Okinawa, which had been under Japanese control, were placed under United States administration after WWII, in 1951. In 1972, they reverted back to Japan. So on July 30th, the entire island had to go from driving on the right hand side of the road, to the left hand side! All of the signs, everything was changed on that one day! Not sure what they did about the steering wheels of the cars, but can you imagine the number of accidents, or near accidents, that must have happened??? I'll send you a picture of the sign they used to remind everyone of the date of change.