The Morning Sweden Changed Sides
About one person in three in the world drives on the left. The other two drive on the right. Nobody planned this.
Long ago, most people rode horses on the left side of the road. Most people are right-handed, so this kept the right hand free. Then came big carts, pulled by four or six horses. In the United States the driver sat on the left horse at the back, and he could see the road better when he drove on the right. Slowly, the right side won there.
France moved to the right too, and French rule carried the change across much of Europe. In contrast, Britain made the left side official in a law of 1835. British ships and British trains then took the left side to India, Australia and South Africa. Japan was never British, but it built its first railways with British help, and it kept the left as well.
So the map today is really a map of old habits, including one very famous change of mind. On the morning of 3 September 1967, Sweden drove on the left. That afternoon, it drove on the right. The cars stopped, moved over, and started again.
Why? Not because one side is better. Sweden has long land borders with Norway and Finland, and both of them drove on the right. The main factor was the neighbors.