Ever wonder why people drive on the left in some countries and on the right in others? Although there isn't a consensus on how these roadway guidelines developed, a few theories, based on archeological discoveries, historical research, and common sense, have been offered.
It appears that driving on the left was the original preference. The majority of the world's people are right-handed. A right-handed swordsman would hang his scabbard on his left side so that he could draw his sword with his right hand. With sword in hand, a mounted swordsman would want to hold the reins with his left hand, keeping his right sword hand free should any trouble ensue. By keeping oncoming "traffic" on his right, he wouldn't risk severing his own horse's neck by swinging his sword across his body. He therefore would prefer to ride on the left side of the road.
The first traffic flow mandate came in the 14th century from Pope Boniface "All-Roads-Lead-to-Rome" VIII, who declared that all pilgrims to Rome should stick to the left side of the road.
Some historians believe that the switch to the now more popular right-hand driving began in France during the French Revolution. One explanation is that, up until that time, aristocrats would drive their expensive carriages on the left, forcing the peasants to walk on the right. When upper-class heads began to roll, those aristocrats decided that standing out in the crowd probably wasn't a good idea and joined the peasants on the right side of the road. An alternative explanation is that Robespierre and his whole Jacobin (French Protestant) clan mandated that French people should drive on the right simply in defiance of the Church and Pope Boniface VIII's decree.
Either way, as Napoleon's armies spread over and conquered much of Europe, so to did the French habit of driving on the right. Since Napoleon never conquered England, England stayed left. To this day, there are connections between driving and the French and British empires: for the most part, in countries that were part of the British Empire, people drive on the left; in countries that were part of Napoleon's empire, people drive on the right. Other countries eventually adopted driving rules that were on par with their neighbors.
But what about the United States? Some have claimed that Americans decided to drive on the right in simple defiance of British standards. Others have pointed out differences in transportation that made right-side driving more convenient in the young United States. Early large wagons, like the Conestoga, were pulled by teams of horses or oxen and didn't have a seat for the driver. Drivers would sit on the back-left horse (the postilion position) so that they could wield their whips in their right hands. They would naturally want to pass oncoming "traffic" on the right so that they could make sure that their wheel hubs didn't collide with those of the other wagon.
Theories abound, and we may never know for sure. Regardless, most countries dictate driving on the right — 65% to 70% depending on whether you consider population, geographic size, number of cars, or total length of roadways. And that percentage occasionally grows — Sweden, Iceland, Austria, and others all switched to right-side driving during the 20th century.
