Straight Dope provides some historical facts:
?In the Middle Ages you kept to the left for the simple reason that
you never knew who you'd meet on the road in those days. You wanted to
make sure that a stranger passed on the right so you could go for your
sword in case he proved unfriendly.
This custom was given official sanction in 1300 AD, when Pope Boniface
VIII invented the modern science of traffic control by declaring that
pilgrims headed to Rome should keep left.
The papal system prevailed until the late 1700s, when teamsters in the
United States and France began hauling farm products in big wagons
pulled by several pairs of horses.
These wagons had no driver's seat. Instead the driver sat on the left
rear horse, so he could keep his right arm free to lash the team.
Since you were sitting on the left, naturally you wanted everybody to
pass on the left so you could look down and make sure you kept clear
of the other guy's wheels. Ergo, you kept to the right side of the
The first known keep-right law in the U.S. was enacted in Pennsylvania
in 1792, and in the ensuing years many states and Canadian provinces
According to World Standards, automobiles in the USA changed to
left-hand-drive in the early 1900s because it was more practical to
have the driver seated near the centre line of the road in order to
see the space available when passing oncoming cars, and to allow
front-seat passengers to get out of the car onto the pavement instead
of into the middle of the street
?All early automobiles in the USA (driving on the right-hand side of
the road) were right-hand-drive, following the practice established by
horse-drawn buggies. They changed to left-hand-drive in the early
1900s as it was decided that it was more practical to have the driver
seated near the centreline of the road, both to judge the space
available when passing oncoming cars, and to allow front-seat
passengers to get out of the car onto the pavement instead of into the
middle of the street.
Ford changed to left-hand-drive in the 1908 model year. A Ford
catalogue from 1908 explains the benefits of placing the controls on
the left side of the car:
?The control is located on the left side, the logical place, for the
following reasons: Travelling along the right side of the road the
steering wheel on the right side of the car made it necessary to get
out on the street side and walk around the car. This is awkward and
especially inconvenient if there is a lady to be considered. The
control on the left allows you to step out of the car on to the
curbing without having had to turn the car around.
In the matter of steering with the control on the right, the driver is
farthest away from the vehicle he is passing, going in opposite
direction; with it on the left side he is able to see even the wheels
of the other car and easily avoids danger.?
From the Old Farmer?s Almanac:
?About a quarter of the world's countries drive on the left, and the
countries that do are mostly former British colonies. This quirk
perplexes the rest of the world; however, there is a perfectly good
reason. Up to the late 1700s, everybody traveled on the left side of
the road because it was the sensible option for feudal, violent
societies. Because most people are right-handed, jousting knights with
their lances under their right arm naturally passed on each other's
right, and if you passed a stranger on the road, you walked on the
left to ensure that your protective sword arm was between yourself and
?The drive-on-the-right policy was adopted by the United States, which
was anxious to cast off all remaining links with its British colonial
past. Once America drove on the right, left-side driving fell out of
favor, because America was once the only manufacturer of reliable
The Old Farmer?s Almanac
?France overturned this practice as part of its sweeping social
rethink. A change was carried out all over continental Europe by
Napoleon. The reason it changed under Napoleon was because he was left
handed his armies had to march on the right so he could keep his sword
arm between him and any opponent.
From then on, any part of the world which was at some time part of the
British Empire was thus left hand and any part colonized by the French
was right hand.
In America, the French colonized the southern states (Louisiana for
instance) and the Canadian east coast (Quebec). The Dutch colonized
New York (or New Amsterdam). The Spanish and Portugese colonized the
southern Americas. So The British were a minority in shaping the
Here is an excellent publication that explains which side of the road
people drive on, the history of this practice and the reasons why. For
reasons of copyright, I cannot post the entire article here; I suggest
that read these pages in their entirety at the following link.
Search terms used:
British drive on left
Americans OR ?United States? drive on the right +history
I hope you find this information helpful!