Why do some countries drive on the left side of the road and others on the right?

The choice between driving on the left or the right side of the road is largely rooted in historical tradition rather than modern traffic safety.

Driving on the Left Historically, most people were right-handed. When traveling on horseback or in carts, people preferred to keep to the left. This kept their dominant right hand free to hold a weapon (like a sword) or a whip, in case they encountered an oncoming stranger or needed to control their team. In medieval times, traveling on the left was a defensive posture. This practice was formally codified in Great Britain by the 18th century and subsequently spread to the countries of the British Empire.

Driving on the Right The shift to the right is often attributed to Napoleon Bonaparte and the rise of large freight wagons. As the use of heavy wagons (pulled by multiple pairs of horses) increased, teamsters found it easier to sit on the left-most horse to control the team with their right hand. By driving on the right side of the road, the driver had a better view of oncoming traffic passing to their left.

Napoleon enforced the "keep right" rule across much of Continental Europe during his conquests. Countries that were not part of the French Empire or under British influence generally chose their side based on proximity to neighbors or through their own localized customs.

Why the split remains In the early 20th century, the rise of the automobile forced countries to standardize. Many countries that were part of the British Empire kept the left-hand rule. However, many other nations transitioned to the right to align with their neighbors or to match the design of mass-produced vehicles—notably the Ford Model T, which was designed with the driver’s seat on the left, making it much safer to drive on the right side of the road.

Today, about 65% of the world's population lives in countries that drive on the right, while about 35% live in countries that drive on the left (mostly former British colonies, Japan, Thailand, and some island nations).