How Do Countries Choose Which Side They Drive On?

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.

Big Questions
What is Mercury in Retrograde, and Why Do We Blame Things On It?

Crashed computers, missed flights, tensions in your workplace—a person who subscribes to astrology would tell you to expect all this chaos and more when Mercury starts retrograding for the first time this year on Friday, March 23. But according to an astronomer, this common celestial phenomenon is no reason to stay cooped up at home for weeks at a time.

"We don't know of any physical mechanism that would cause things like power outages or personality changes in people," Dr. Mark Hammergren, an astronomer at Chicago's Adler Planetarium, tells Mental Floss. So if Mercury doesn’t throw business dealings and relationships out of whack when it appears to change direction in the sky, why are so many people convinced that it does?


Mercury retrograde—as it's technically called—was being written about in astrology circles as far back as the mid-18th century. The event was noted in British agricultural almanacs of the time, which farmers would read to sync their planting schedules to the patterns of the stars. During the spiritualism craze of the Victorian era, interest in astrology boomed, with many believing that the stars affected the Earth in a variety of (often inconvenient) ways. Late 19th-century publications like The Astrologer’s Magazine and The Science of the Stars connected Mercury retrograde with heavy rainfall. Characterizations of the happening as an "ill omen" also appeared in a handful of articles during that period, but its association with outright disaster wasn’t as prevalent then as it is today.

While other spiritualist hobbies like séances and crystal gazing gradually faded, astrology grew even more popular. By the 1970s, horoscopes were a newspaper mainstay and Mercury retrograde was a recurring player. Because the Roman god Mercury was said to govern travel, commerce, financial wealth, and communication, in astrological circles, Mercury the planet became linked to those matters as well.

"Don’t start anything when Mercury is retrograde," an April 1979 issue of The Baltimore Sun instructed its readers. "A large communications organization notes that magnetic storms, disrupting messages, are prolonged when Mercury appears to be going backwards. Mercury, of course, is the planet associated with communication." The power attributed to the event has become so overblown that today it's blamed for everything from digestive problems to broken washing machines.


Though hysteria around Mercury retrograde is stronger than ever, there's still zero evidence that it's something we should worry about. Even the flimsiest explanations, like the idea that the gravitational pull from Mercury influences the water in our bodies in the same way that the moon controls the tides, are easily deflated by science. "A car 20 feet away from you will exert a stronger pull of gravity than the planet Mercury does," Dr. Hammergren says.

To understand how little Mercury retrograde impacts life on Earth, it helps to learn the physical process behind the phenomenon. When the planet nearest to the Sun is retrograde, it appears to move "backwards" (east to west rather than west to east) across the sky. This apparent reversal in Mercury's orbit is actually just an illusion to the people viewing it from Earth. Picture Mercury and Earth circling the Sun like cars on a racetrack. A year on Mercury is shorter than a year on Earth (88 Earth days compared to 365), which means Mercury experiences four years in the time it takes us to finish one solar loop.

When the planets are next to one another on the same side of the Sun, Mercury looks like it's moving east to those of us on Earth. But when Mercury overtakes Earth and continues its orbit, its straight trajectory seems to change course. According to Dr. Hammergren, it's just a trick of perspective. "Same thing if you were passing a car on a highway, maybe going a little bit faster than they are," he says. "They're not really going backwards, they just appear to be going backwards relative to your motion."

Embedded from GIFY

Earth's orbit isn't identical to that of any other planet in the solar system, which means that all the planets appear to move backwards at varying points in time. Planets farther from the Sun than Earth have even more noticeable retrograde patterns because they're visible at night. But thanks to astrology, it's Mercury's retrograde motion that incites dread every few months.

Dr. Hammergren blames the superstition attached to Mercury, and astrology as a whole, on confirmation bias: "[Believers] will say, 'Aha! See, there's a shake-up in my workplace because Mercury's retrograde.'" He urges people to review the past year and see if the periods of their lives when Mercury was retrograde were especially catastrophic. They'll likely find that misinterpreted messages and technical problems are fairly common throughout the year. But as Dr. Hammergren says, when things go wrong and Mercury isn't retrograde, "we don't get that hashtag. It's called Monday."

This story originally ran in 2017.

Big Questions
What Is Fair Trade?

What is fair trade?

Shannon Fisher:

Fair trade is a system of manufacturing and purchasing intended to:

1) level the economic playing field for underdeveloped nations; and

2) protect against human rights abuses in the Global South.

Fair trade farmers are guaranteed fair market prices for their crops, and farm workers are guaranteed a living wage, which means workers who farm fair trade products and ingredients are guaranteed to earn enough to support their families and comfortably live in their communities. There are rules against inhumane work practices. Fair trade farming organizations are monitored for a safe work environment, lack of discrimination, the freedom to organize, and strict adherence to child labor laws. Agrochemicals and GMOs are also forbidden. If these rules are not followed, a product will not receive fair trade certification.

The quality of life in many communities producing fair trade-certified goods is greatly improved. Sometimes, farming communities are given profit sharing from the companies that source their ingredients, and those profits go to improving the community as a whole—be it with a library, medical facilities, town infrastructure, or opening small businesses to support the residents. A major goal of fair trade is to help foster sustainable development around the globe. By helping farming communities in third-world countries, the economy of the entire region gets a boost.

This post originally appeared on Quora. Click here to view.


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