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.