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In 2009, the country of Samoa prohibited the
sale of alcohol ---- for three days ---- to

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keep people safe while the island nation switched
from driving on the right side of the road

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to driving on the left. The switch was so
Samoans could get cheap "hand-me-down" cars

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from nearby left-side driving New Zealand
and Australia. But Samoans weren't too pleased,

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since most of the cars they owned were designed
to drive on the right. In fact, 2 out of 3

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earthlings drive on the right.

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But why? ... There aren't clear and obvious
reasons to choose one side over the other,

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so the origin of driving conventions is a
perfect opportunity for the mathematics of

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game theory and symmetry breaking. Or we can
just look at historical evidence.

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Today's rules evolved from "driving" livestock
and carts on the earliest roads. Archaeologists

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view deeper grooves on the left lane leaving
an ancient Roman quarry in England as evidence

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for left-side traffic, since departing wagons
would've had heavier loads. And it's possible

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that this left side convention was in place
so right-handed soldiers and knights could

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draw their weapons more quickly against passing
enemies.

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Whatever the reason, keeping to the left was
eventually made into law in England in 1835.

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And today, most people who drive on the left
side live in countries, like India, South

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Africa, and Australia, which were once British
colonies.

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But that doesn't explain why the rest of the
world drives on the right.

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Some claim that following the French Revolution,
drivers there switched to the right to reject

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the practices of their overthrown aristocracy,
but others suggest the French drove on the

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right all along. Regardless, driving on the
right side of the road did spread across much

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of Europe when Napoleon (and later Hitler)
imposed their national driving rules on conquered

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territory.

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And other countries voluntarily switched to
the right to align with their neighbors, like

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Sweden in 1967, or to veer away from their
colonial pasts, like Nigeria and Ghana in

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the 1970s.

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And in the US? Well, America owes its right-sided
habit, in part, to the carts and postilion

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wagons of its early days. Driving either from
the ground or from horseback, right-handed

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men preferred to walk or ride on the left
side of the horses so they could control the

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animals with their right hand. As a result,
they drove their wagons to the right in order

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to be seated near the center of the road,
to see and steer clear of oncoming traffic.

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And that's ultimately the point of driving
laws: to keep us safe from the high-speed,

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two-ton metal projectiles we call cars.