7 Answers

Answer:

The British custom of driving on the left was passed down from the Romans.  The chariot driver stayed to the left in order to meet an approaching enemy with his right sword hand.  Americans switched to driving  on the right because on covered wagons the brakes were built on the left, forcing the driver to sit on the same side and, consequently, to drive on the right in order they could have a clear view of the road.

Right– and left hand traffic

Taken from Wikipedia

History

In 1998, archaeologists found a well-preserved track leading to a Roman quarry near Swindon, England. The grooves in the road on the left side (viewed facing down the track away from the quarry) were much deeper than those on the right side. These grooves suggest that the Romans drove on the left, at least in this particular location, since carts would exit the quarry heavily loaded, and enter it empty. 

The history of the keep-left rule could be tracked back to ancient Greece, Egypt and Rome. In retrospect, it was more widely practised than right-side traffic. Ancient Greeks, Egyptians and Romans adhered to the left side while marching their troops. If two men riding on horseback were to start a fight, each would edge toward the left. Thus, they would be enabled to draw swords from their right and uphold a defensive position. Eventually, this turned into custom, and later, a law. The keep-left rule was formally established in ancient Rome. Resulting from congestions in the city, strict traffic rules came into being. Throughout the Roman Empire rules banning wagons and chariots during the day, and wheeled traffic during the night – so as not to disturb citizens from sleep – were promulgated. Thousands of pilgrims arrived to Rome forming one massive celebration of the eternal church. Pilgrims who wished to visit the city were instructed to keep to the left side of the road. By the time the Pope ordered instructions to keep left of the road, this rule was already widely used. The regulation has been practised by some countries ever since. 

In England, however, keeping to the left was perceived more as a custom than a rule. It was due to the increase in horse traffic by the end of the 18th century, that the British Parliament was urged to entrench the keep-left rule into a statute. By 1771, the number of coaches rose from 300 in 1639 to 1000.  The first legal reference in Britain to an order for traffic to remain on the left was in 1756 with regard to London Bridge. Disobeyers would have to pay a penalty of 20 shillings. Increasing demand for improvement of traffic and roads in the world of growing economy, commerce, agriculture and industry encouraged the passing of the General Highway Act in 1773 consolidating regulations of individual roads. The Highway Act 1773 contained a recommendation that horse traffic should remain on the left and this is enshrined in the Highway Act 1835. In the late 18th century, the shift from left to right that took place in countries such as the United States was based on 'teamsters' use of large freight wagons pulled by several pairs of horses. The wagons had no driver's seat, so a postilion sat on the left rear horse and held his whip in his right hand. Seated on the left, the driver preferred that other wagons pass him on the left so that he could be sure to keep clear of the wheels of oncoming wagons. He did that by driving on the right side of the road. 

Full article – http://en.wikipedia.org/wiki/Right-_and_left-hand_traffic 

I think in Japan as well.  What's the answer?

Its still the same because they switch sides of the steering wheels whilst we may drive on different sides of the road the rules are similar just in reverse.

We use the left side of our brain more than our right , they say the left side is rational and the right is emotional , or is it the other way around :))) we get American cars here the steering wheel is on the left :) ours is on the right

I drove on the "wrong" side of the road when I visited Australia, it was easy enough to do, however when coming out of a rotary (round-a-bout) it got weird for me.   The Aussie relatives got a big kick out of if, and when they came to the states, I took them to a rural area to drive.   They were very nervous, and didn't want any part of it! 

To stay on the right side of the law, they must drive on the left side, simple.

About Roman chariots. It is said that the track ( the distance between the wheels) was 4ft 81/2 inches ( 1437mm) as seen from the ruts left in the roads. This was because of the width of the horses used to pull the chariots.  Most carts in England used this measurement and Robert Stevenson  continued it when planning the first railways and Standard Gauge is still used in most countries.