Why do some countries drive on the left side of the road while others drive on the right, and what historical factors determined these different driving patterns around the world?

-Karthik Gurumurthy

Honestly, this is not a science question but more  a general trivia one. The question of why some countries drive on the left while others drive on the right reveals a fascinating tale of historical, cultural, and political influences that have shaped our modern traffic systems.

In almost all countries, the driver sits on the side of the car closest to the centerline of the road. This positioning gives drivers the best visibility for oncoming traffic and passing maneuvers. Currently, the world is divided: 165 countries drive on the right side with left-hand drive vehicles (like the United States), while 75 countries drive on the left with right-hand drive vehicles (like the United Kingdom).

This division traces back to medieval times. When travelers passed each other on roads, most people—being right-handed—preferred to keep to the left. This positioning allowed them to keep their dominant hand toward potential threats, ready to draw their sword if necessary. Mounting horses from the left side (easier for right-handed individuals) meant the sword hung on the left hip and could be drawn across the body with the right hand. This practice was formalized when Pope Benefice issued an edict in the 1300s recommending left-side travel, and the United Kingdom officially codified it into law in 1773, later incorporating it into the Highway Bill of 1835.

The shift toward right-side driving gained momentum during the French Revolution in the 1790s. French aristocrats traditionally sped their carriages along the left side, forcing common pedestrians to the right side of roads. When the revolution began and aristocrats were being executed, many nobility attempted to blend in with common citizens by adopting right-side travel. This practice was officially recorded in Paris in 1794.

As Napoleon expanded the French Empire, he imposed right-side driving throughout conquered territories including the Low Countries, Germany, Russia, Poland, Spain, Italy, and Switzerland. Meanwhile, the British Empire maintained left-side driving, spreading this practice to its colonies including Australia, India, and much of Africa.

The American preference for right-side driving likely came through French influence, particularly via General Lafayette during the Revolutionary War. The Lancaster to Philadelphia turnpike, established in 1792, provides the first documented reference to right-side driving in the United States.

Canada presents a particularly interesting case study in this evolution. Provinces with French influence, like Quebec, traditionally drove on the right, while British-influenced regions such as British Columbia and the Atlantic provinces drove on the left. These British-influenced provinces switched to right-side driving in the 1920s, with the remaining Canadian territories following suit after World War II, creating nationwide consistency.

Today, this historical divide remains visible in global driving patterns, with former British colonies generally driving on the left and countries influenced by continental European powers driving on the right—a daily reminder of how historical political relationships continue to influence our modern lives.