0:00:01.011,0:00:05.096
In 2009, the country of Samoa prohibited the[br]sale of alcohol ---- for three days ---- to

0:00:05.096,0:00:09.839
keep people safe while the island nation switched[br]from driving on the right side of the road

0:00:09.839,0:00:14.009
to driving on the left. The switch was so[br]Samoans could get cheap "hand-me-down" cars

0:00:14.009,0:00:18.059
from nearby left-side driving New Zealand[br]and Australia. But Samoans weren't too pleased,

0:00:18.059,0:00:22.099
since most of the cars they owned were designed[br]to drive on the right. In fact, 2 out of 3

0:00:22.099,0:00:24.094
earthlings drive on the right.

0:00:24.094,0:00:29.019
But why? ... There aren't clear and obvious[br]reasons to choose one side over the other,

0:00:29.019,0:00:32.007
so the origin of driving conventions is a[br]perfect opportunity for the mathematics of

0:00:32.007,0:00:36.034
game theory and symmetry breaking. Or we can[br]just look at historical evidence.

0:00:36.034,0:00:41.056
Today's rules evolved from "driving" livestock[br]and carts on the earliest roads. Archaeologists

0:00:41.056,0:00:45.079
view deeper grooves on the left lane leaving[br]an ancient Roman quarry in England as evidence

0:00:45.079,0:00:50.029
for left-side traffic, since departing wagons[br]would've had heavier loads. And it's possible

0:00:50.029,0:00:54.032
that this left side convention was in place[br]so right-handed soldiers and knights could

0:00:54.032,0:00:57.007
draw their weapons more quickly against passing[br]enemies.

0:00:57.007,0:01:01.048
Whatever the reason, keeping to the left was[br]eventually made into law in England in 1835.

0:01:01.048,0:01:05.129
And today, most people who drive on the left[br]side live in countries, like India, South

0:01:05.129,0:01:08.000
Africa, and Australia, which were once British[br]colonies.

0:01:08.000,0:01:10.092
But that doesn't explain why the rest of the[br]world drives on the right.

0:01:10.092,0:01:15.017
Some claim that following the French Revolution,[br]drivers there switched to the right to reject

0:01:15.017,0:01:19.054
the practices of their overthrown aristocracy,[br]but others suggest the French drove on the

0:01:19.054,0:01:24.014
right all along. Regardless, driving on the[br]right side of the road did spread across much

0:01:24.014,0:01:28.077
of Europe when Napoleon (and later Hitler)[br]imposed their national driving rules on conquered

0:01:28.077,0:01:29.024
territory.

0:01:29.024,0:01:32.909
And other countries voluntarily switched to[br]the right to align with their neighbors, like

0:01:32.909,0:01:37.689
Sweden in 1967, or to veer away from their[br]colonial pasts, like Nigeria and Ghana in

0:01:37.689,0:01:39.014
the 1970s.

0:01:39.014,0:01:44.006
And in the US? Well, America owes its right-sided[br]habit, in part, to the carts and postilion

0:01:44.006,0:01:48.034
wagons of its early days. Driving either from[br]the ground or from horseback, right-handed

0:01:48.034,0:01:51.869
men preferred to walk or ride on the left[br]side of the horses so they could control the

0:01:51.869,0:01:55.059
animals with their right hand. As a result,[br]they drove their wagons to the right in order

0:01:55.059,0:01:59.084
to be seated near the center of the road,[br]to see and steer clear of oncoming traffic.

0:01:59.084,0:02:03.939
And that's ultimately the point of driving[br]laws: to keep us safe from the high-speed,

0:02:03.939,9:59:59.000
two-ton metal projectiles we call cars.