American drivers keep to the right and are usually quite surprised when they first come across drivers from other countries, such as in Britain and the former British colonies, who keep to the left. While it would be easy to chalk this up as just one of those things that’s different just because (like calling fried potato wedges chips in one place and fries in the the other), there’s actually a rather interesting history behind both why the British drive on the left and their American counterparts drive on the right.
The majority of people are right-hand dominant and bladed weapons are traditionally carried on the left side of the body so the dominant hand can draw them. If you travel down the road on the right hand side, that means if you need to draw your weapon in self defense against highway bandits or the like, then your sword will be drawn out from the center of the road and over the ditch. If you’re on foot this means you have to rotate your body inwards to engage the person attacking you, but if you’re on horseback, it’s nearly impossible as now you need to quickly and deftly orient your horse so that your sword arm is centered to the road and your attacker. The practical solution, and the one adopted by the British centuries ago, was to simply travel so that your strong arm is always center to the lane of travel and a drawn sword will always face someone approaching you. The tradition spread with the British empire and, in the 14th century, it was even sanctioned by Pope Boniface VIII who instructed all pilgrims headed to Rome to keep to the left side of the road.
So why did such a long-standing (and practical) solution fall by the wayside? Just like people adopted left-side travel for pragmatic reasons, right-side travel was adopted for equally pragmatic reasons. In the late 18th century teamsters, wagon drivers who drove large teams of draft animals to haul goods, would sit on the rear left animal in their draft team so that they could use their right arm to reach every animal in the team with their whip. Because they were seated on the rear left side, it was very difficult to see the right side of the wagon (and any traffic on that side that might result in a collision) so they took to driving the wagons on the right side of the road so they could easily see oncoming wagons and avoid collisions between both animals and the freight they were hauling.
One would think the same shift in technology and commerce practices would yield a similar result in Britain wherein British teamsters would also begin driving on the right side of the road, but the smaller British roads and wagons conspired to keep things left-side only. British wagons were smaller and the driver would sit on the wagon itself instead of on one of the draft animals. When you’re on the wagon it makes more sense to sit on the right-hand side of the bench because when you whip with your right hand, the whip will fly back over your right shoulder and into the empty space beside the wagon (instead of potentially snagging on the wagon payload as it would if you were sitting on the left side and whipping with your right hand). As such British teamsters kept right, stayed right, and the people of Britain are still traveling on the left side of the road with their right arms at-the-ready as their sword-bearing forefathers did over a millennium ago.