Why do the English drive on the left?

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 road.

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 followed suit.

In France the keep-right custom was established in much the same way. An added impetus was that, this being the era of the French Revolution and all, people figured, hey, no pope is gonna tell ME what to do.

Later Napoleon enforced the keep-right rule in all countries occupied by his armies. The custom endured even after the empire was destroyed.

In small-is-beautiful Britain, though, they didn't use monster wagons that required the driver to ride a horse. Instead the guy sat on a seat mounted on the wagon.

What's more, he usually sat on the right side of the seat so the whip wouldn't hang up on the load behind him when he flogged the horses. (Then as now, most people did their flogging right-handed.)

So the English continued to drive on the left, not realizing that the tide of history was running against them and they would wind up being ridiculed by folks like you with no appreciation of life's little ironies.

Keeping left first entered English law in 1756, with the enactment of an ordinance governing traffic on the London Bridge, and ultimately became the rule throughout the British Empire.

The trend among nations over the years has been toward driving on the right, but Britain has done its best to stave off global homogenization.

Its former colony India remains a hotbed of leftist sentiment, as does Indonesia, which was occupied by the British in the early 19th century. The English minister to Japan achieved the coup of his career in 1859 when he persuaded his hosts to make keep-left the law in the future home of Toyota and Mitsubishi.

Nonetheless, the power of the right has been growing steadily. When Germany annexed Austria in 1938, it brutally suppressed the latter's keep-left rights, and much the same happened in Czechoslovakia in 1939.

The last holdouts in mainland Europe, the Swedes, finally switched to the right in 1967 because most of the countries they sold Saabs and Volvos to were righties and they got tired of having to make different versions for domestic use and export.

Explanation taken from: Cecil Adams, "Return of the Straight Dope" (New York: Ballantine Books, 1994).