Why Do We Drive on Different Sides of the Road?

Considering how much time I spend thinking about cars, there's one extremely basic thing about driving that I somehow never thought much about: Why does half the world seem to be driving on the wrong side of the road?

And, more importantly, who decided which side was wrong?

I ended up going down a bit of a rabbit hole on this, and the answer goes back much further than cars.

People have theories about travelers keeping to the left hundreds of years ago because most people were right-handed. Staying on the left could leave your dominant hand free when passing a stranger, which was apparently a more serious concern when traveling involved horses, swords and a much higher chance of being robbed.

The right-hand tradition developed differently. One commonly cited influence is large horse-drawn wagons, particularly in places like the United States and France. Drivers could sit toward the left to control the horses with their right hands, making it more practical to keep their vehicles to the right so they could better judge passing traffic.

Then history made everything even messier. European powers carried their road systems into territories around the world. Britain generally kept left, and many places once under British rule still do today, including Australia, India and South Africa. Much of continental Europe went right, and that system spread elsewhere too.

By the time cars arrived, switching sides wasn't exactly simple. Roads, intersections, signs and eventually entire vehicles were being designed around whichever system a country already used. Once millions of people learn one way of doing something, there's a pretty good argument for leaving it alone.

Some countries did switch, though. Sweden famously changed from driving on the left to driving on the right in 1967. The day even had a name, Dagen H, and the country had to change road signs, intersections and traffic systems while preparing millions of drivers to suddenly reverse a habit they had followed their entire lives.

As someone with Swedish parents who was born in London and has spent a lot of my life moving between countries, I find the whole thing pretty funny. Driving on one side feels completely obvious until you arrive somewhere where everyone confidently does the exact opposite.

It's also one of those tiny reminders of how much history is hiding inside completely ordinary parts of life. We don't wake up and think about centuries of trade, empires, horses and infrastructure when we pull onto a road. We just turn left or right. Hopefully the correct one.