How history and horses decided which side of the road we use

HostMost of us don't think twice about which side of the road we're on until we travel somewhere and it's the "wrong" way. It feels like such a basic rule, but it turns out it's actually tied back to how people used to fight on horseback. How did a sword fight in the middle ages end up deciding how we get to the grocery store today?

GuestWell, it all starts with the fact that about nine out of ten people are right-handed. If you were traveling hundreds of years ago, you weren't worried about car crashes; you were worried about someone jumping out of the woods to rob you. If you stayed on the left side of the path, your right hand—the one holding your sword—was always closer to the person coming toward you. You were basically in the best spot to defend yourself at a moment's notice. This wasn't just a habit, either. It was the standard for anyone with a weapon and a horse. It was so common that in the year thirteen hundred, Pope Boniface the Eighth even told pilgrims traveling to Rome that they had to keep to the left. For a long time, the left side was just the side of the warrior and the rich.

HostSo if the left side was the default for anyone with a sword, why did so much of the world end up switching over to the right?

GuestThat shift started in the late seventeen hundreds because of these massive freight wagons. Think of things like the Conestoga wagons in America or the huge haulers they had in France. These wagons were often pulled by teams of six or eight horses. The big thing here is that they didn't have a seat for the driver. Instead, the driver sat on what they called the near horse, which was the horse at the very back on the left side of the team. By sitting there, he could keep his right hand free to use his whip on all the other horses in front of him.

HostHmm, but why does sitting on the left horse mean you have to drive on the right side of the road? I would think you would still want to stay on the left.

GuestIt's all about the view. If you're sitting on that back-left horse and another giant wagon is coming at you from the other direction, you want to be sure your wheels don't bash into their wheels. To get a clear look at that, you want the other wagon to pass by on your left side so you can look straight down at the gap. To make that happen, both wagons have to pull over to the right side of the road. Those big wagons were so common that they basically forced the rules of the road to change to fit them.

HostOkay, that makes sense for the big wagons, but it feels like there's a deeper split, especially when you look at Europe. How did it turn into such a political thing?

GuestThat's where the French Revolution comes in. Before the revolution, the rich people in France traveled on the left and forced the poor people over to the right. When the rebels took over, they wanted to show that everyone was equal now, so they ordered everyone to stay on the right side. It was a huge symbolic gesture. Then Napoleon Bonaparte came along. As he conquered his way across Europe, he made right-hand traffic the law in every place he took over, from the Netherlands to the German states and Poland.

HostBut Britain stayed on the left. Was that just because they were an island?

GuestIt was more about who they were fighting. Britain was one of the big powers that Napoleon could never beat, so they stuck to their left-hand traditions almost as a way to stand up to him. This ended up creating a kind of political map of the world. The countries Napoleon touched, and the places they later settled, drove on the right. The British Empire and its territories kept the left-hand rule. For a long time, the side of the road you used basically told the world whose side you were on in the war.

HostIt's wild that a war from two hundred years ago is still deciding our traffic patterns. But eventually, cars had to make things even more complicated, right?

GuestThey did. In the early days, car makers put the steering wheel on whichever side they felt like. But then Henry Ford changed everything. In nineteen oh eight, he made the left-hand drive standard in the Model T. If your steering wheel is on the left, you really need to drive on the right side of the road to see oncoming traffic and turns clearly. Because Ford sold so many cars, he basically forced a global standard. Over time, countries started switching sides just to match their neighbors and make trade easier.

HostThat sounds like a total nightmare to coordinate. I mean, how do you even tell an entire country to just start driving the opposite way one morning?

GuestIt was a massive undertaking. The most famous case is Sweden in nineteen sixty seven. They called it Dagen H. They had been driving on the left, but all their neighbors drove on the right, and most of the cars in Sweden were already built with steering wheels on the left side anyway. So, they decided to switch the whole country to the right side overnight. They had to change every sign and road marking in the country in a matter of hours. People went to sleep driving on the left and woke up having to remember to stay on the right.

HostThose ancient sword fights and heavy horse wagons are still sitting right there under the surface of every road we drive on.

GuestEven today, the map of who drives where's really just a leftover record of which empires won and which car companies sold the most engines.

HostOur modern commute is still following a path carved out by medieval knights and the hands they used to hold their weapons.