Why a third of the world drives on the left

Look at a world map of traffic rules and you'll find a puzzle: about 35% of countries drive on the left, and they hold roughly a third of the planet's population. The pattern isn't random — it's a fossil record of empire, invasion, and old habits that outlasted the horse-drawn carriages that created them.

The left-hand tradition traces back to a time when most people were right-handed and armed. Riders kept to the left so their sword arm faced oncoming strangers, and mounting a horse from the left curbside was safer. This custom spread across the British Empire, which is why India, Australia, South Africa, Japan, and much of the Caribbean still keep left today. Japan adopted it partly through British-built railways, never having been a colony.

The switch to the right is often linked to France. Large wagons pulled by teams of horses had the driver sit on the rear-left horse to whip with his right hand — making it natural to pass oncoming traffic on the right. Napoleon spread right-hand driving across the Europe he conquered, and the young United States embraced it as a break from British custom. When cars arrived, countries simply mechanized whatever side they already used.

Switching sides is so disruptive that it's now extremely rare. When Sweden changed from left to right in 1967 — a day nicknamed "Dagen H" — the entire country reorganized its roads, signs, and buses overnight, and later saw a temporary drop in accidents as nervous drivers slowed down.