Chaos has descended this week on the tiny Pacific island of Samoa after government officials decided to force the entire nation to switch sides of the road on Monday. While Samoan officials insist there have been no accidents as a result of asking drivers to switch from driving on the right side of the road to driving on the left, many non-driving Samoans have been left stranded because the island’s buses now open to the middle of the road.

Samoa is the first nation since the 1970s to switch sides and did so, they say, to end their reliance on left-hand drive vehicles imported at great expense from America. All well and good, but the real question here is why do different nations drive on different sides of the roads? Here in England, where traffic comes from the right, it took me more than a few weeks to stop looking left every time I went to cross the street—training that was completely undone when I went to France for two weeks at the end of the summer.

So what is the deal with the “wrong” side of the road? How do countries decide which side they drive on?

Because The Pope Said So

According to some sources, about a quarter of the world drives on the left, as they do in Britain. This isn’t too surprising, since at one time Britain owned about a quarter of the world. Traveling on the left side of the road was a practice that started with the feudal societies of Western world, like the proto-British empire – back in the day, you never knew who’d you pass on the road, so best to keep your sword arm between you and them. In 1300 AD, Pope Boniface VIII codified the practice with a law that decreed that pilgrims headed for Rome should keep on the left.

The Birth of the Left-Hand Drivers’ Seat

Things were going fine until the advent of market-based agriculture on a grand scale. In the 1700s, farmers in the US and France began hauling their products to market in big rigs pulled by many horses. Because these wagons typically had no place to sit, drivers would sit on the rear left horse, with their right arm free to whip the team along – and the left-hand drivers’ seat was born. Drivers naturally tended to ride on the right side of the road now, because it was safer to meet oncoming vehicles from where you could see their wheels. In 1792, a Pennsylvania law required that vehicles keep right, other states following soon after.

Because Napoleon Said So

Another explanation blames Napoleon. Because Napoleon was left-handed, he demanded that everyone approach from the right, so he could keep his sword arm between himself and anyone he’d meet. That’s not exactly true; the custom of keeping to the right actually pre-dated Napoleon, but he did make sure his troops followed it whilst they spread their Empire, and from Napoleon’s lips to law. Switzerland, Germany, Italy, Poland, and Spain, which were all at one point under Napoleon’s either direct control or influence, subsequently drive on the right.

It’s an England/France Thing

So on two different continents, the “keep right” rule was becoming entrenched – while in England, keeping left remained the only way to go, especially after a 1756 city ordinance decreed that all traffic on the London Bridge must keep to the left. From there, it was all about influence.

Though not a hard and fast rule, places that were under French and US influence kept right, while those under the British Empire and its influence still kept left.

In Japan in 1859, for example, a British ambassador was able to convince the government there to keep left, a major coup for the lefties and Britain (this is what the Brits say; the Japanese, however, may disagree and claim that their decision to keep left had more to do with samurai warriors and their needs).

Because Hitler Said So

With the invention of the automobile, countries had good reason to pick a side and stick to it, although not all did. By 1938, there was another reason: Wherever Hitler invaded, he forced the native populations to drive on the right. Parts of Austria, including Vienna, Hungary and Czechoslovakia, that had historically driven on the left now had to drive on the right.

Ask Your Neighbors

Countries were still making “which side?” decisions well into the second half of the 20th century. Sweden, for example, switched to driving on the right in 1967 because by then, most of the countries their burgeoning car industry sold to were right-side countries. By this time, the clearest indicator of which side a country drives on became what its neighbors did, and with whom they traded.

Of course, some places, like the US Virgin Islands, confuse the issue even more by driving left-hand side cars on the left side of the road – it’s the only place under US purview that does so.

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