The United States and almost three-quarters of all countries drive on the right side of the road. Theories abound on why some countries choose right and others left.

The sword and the scabbard

A widely held theory proposes most traffic traveled on the left in the ancient past. Proponents suggest the practice stems from the wearing of weapons. Most people are right-handed. Keeping to the left allows the stronger hand to face an oncoming opponent. This makes some sense, as a swordsman would carry his weapon on the left side of their body. Staying on the left also helps keep the sword away from an enemy.

This might explain the idea of keeping to the left, except evidence suggests other folks did not always follow this. Documents from the middle ages show horse teams, with the driver seated on the left rear horse. Sitting in this position places the right arm nearer the center of the team. A driver seated in this position would very likely wish to travel on the right side of the road. Staying to the right would allow gauging the oncoming vehicles that pass.

The ancient quarry

Others cite evidence from excavation of an ancient Roman quarry that lies in England. Wear on left road bed is far greater than on the right. They feel this suggest the loaded wagons, leaving the quarry traveled on the left. It could also show better road maintenance, on the more valuable right side, where they may have carried loads. This would mean traffic traveled on the right.

The French connection

Before the French revolution, many believe the aristocracy insisted on using the left side of the road. Common people use the right side and traveling on the left is a sign of prestige. After the revolution, practices of the previous ruling class are very unpopular. This could explain the switch to using the right side, which continues till today in France.

During the Napoleonic conquest, they may have widely spread the French practice to conquered lands. This might also explain why England would stubbornly resolve to stay on the left, out of defiance for their enemy.

The port and starboard side

In nautical terms, starboard is the right side of a ship. Most navel vessels designate the starboard side as the "senior" side. The officers' gangway is usually on this side and they usually hoist the pennant of the ship's captain or senior commanding officer on the starboard. This could explain why England and Japan, with their seafaring heritage, might place the driver on the right. With the driver on the right, traveling on the left is more practical.

Early automobiles

Most vehicle builders use a tiller, rather than a steering wheel, on the earliest cars. Such an arrangement is far more simple and does not require a steering gear. They attach the tiller between the front wheels, placing it in the center of the vehicle. A person may drive such a vehicle from either side. A right-handed person might sit on the left, to use their stronger arm to steer. Sitting on the left means the right is a far more likely choice on which to drive.

More sophisticated later designs added the steering wheel. In the early days, these were placed on either side of the vehicle. Henry Ford chooses the left side for the Model T and soon other automakers do the same. It is likely the preference for driving on the right already exist in the United States.

Driving-side becomes law

For obvious reasons, we must regulate traffic flow as the number of vehicles increases. Over the years, laws dictate the side on which we drive, rather than preference. Early rules of the road go into effect in the late seventeen-hundreds. Today most European countries, including France, Germany and Russia and the United States and Canada, drive on the right-hand side of the road. Great Britain and many of their previous colonies, and Japan use the left side.

It is unlikely we will ever know why countries adopt one side or the other. Driving on the left or right works as well and motorists seem happy with things as they are. Perhaps variety is truly the spice of life.

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