In 2009, the country of Samoa prohibited the sale of alcohol ---- for three days ---- to
keep people safe while the island nation switched from driving on the right side of the road
to driving on the left.
The switch was so Samoans could get cheap "hand-me-down" cars from nearby left-side
driving New Zealand and Australia.
But Samoans weren't too pleased, since most of the cars they owned were designed to drive
on the right.
In fact, 2 out of 3 earthlings drive on the right.
But why?
... There aren't clear and obvious reasons to choose one side over the other, so the
origin of driving conventions is a perfect opportunity for the mathematics of game theory
and symmetry breaking.
Or we can just look at historical evidence.
Today's rules evolved from "driving" livestock and carts on the earliest roads.
Archaeologists view deeper grooves on the left lane leaving an ancient Roman quarry
in England as evidence for left-side traffic, since departing wagons would've had heavier
loads.
And it's possible that this left side convention was in place so right-handed soldiers and
knights could draw their weapons more quickly against passing enemies.
Whatever the reason, keeping to the left was eventually made into law in England in 1835.
And today, most people who drive on the left side live in countries, like India, South
Africa, and Australia, which were once British colonies.
But that doesn't explain why the rest of the world drives on the right.
Some claim that following the French Revolution, drivers there switched to the right to reject
the practices of their overthrown aristocracy, but others suggest the French drove on the
right all along.
Regardless, driving on the right side of the road did spread across much of Europe when
Napoleon (and later Hitler) imposed their national driving rules on conquered territory.
And other countries voluntarily switched to the right to align with their neighbors, like
Sweden in 1967, or to veer away from their colonial pasts, like Nigeria and Ghana in
the 1970s.
And in the US?
Well, America owes its right-sided habit, in part, to the carts and postilion wagons
of its early days.
Driving either from the ground or from horseback, right-handed men preferred to walk or ride
on the left side of the horses so they could control the animals with their right hand.
As a result, they drove their wagons to the right in order to be seated near the center
of the road, to see and steer clear of oncoming traffic.
And that's ultimately the point of driving laws: to keep us safe from the high-speed,
two-ton metal projectiles we call cars.