Thought this might be of interest. The European part is apparently from an
article in New Scientist (UK) and the US bit's from a Bill Bryson book. It
educated me a little, but that's not hard :-)
In pre-revolutionary France, carriages, etc rode on the left hand side of
the road. The driver sat on the right hand side of the vehicle so that he
could have his whip in his right (***) hand. When two carriages are
passing on a narrow road it is better to pass driver to driver so as it is
easier to see how much space one has. Therefore carriages rode on the left
hand side of the road. Of course, in pre-revolutionary France, only the
nobility had carriages, the peasantry walked. Then, as now, if you are
walking along a road used by vehicles, you walk on the opposite side so
that you are facing the oncoming traffic. Therefore travelling on the left
was associated with the nobility and travelling on the right with the
peasantry. In post revolutionary France, nobody wanted to be thought a
member of the aristocracy, so everybody changed to driving on the right,
and I believe the practice was enshrined in law before Napoleon cam along.
What Napoleon did was to take the drive on the right rule to large
chunks of Western Europe that he conquered. Subsequently Hitler extended
it further to countries like Czechoslovakia, which until WW2 also drove on
the left.
Of more interest is why North America drives on the right rather than the
left. This has more to do with the prairie schooners (the carriages used
to cross the wilderness. There was no need for whips, and so the drivers
sat on the left hand side of the carriage. This allowed them to keep the
reins in their right (***) hand, and meant that the brake lever was
on the left hand side of the carriage. To allow carriages to pass driver
to driver, they had to drive on the right hand side of the path.
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Andrew McP... member of the nobility, obviously ;-)