Old news, I know, but I can't resist. Available on about a million useless fact web pages.
Until 1965, driving was done on the left-hand side on roads in Sweden. The conversion to right-hand was done on a week day at 5 pm. All traffic stopped as people switched sides. This time and day were chosen to prevent accidents where drivers would have gotten up in the morning and been too sleepy to realize this was the day of the changeover.
As a part-Swede I can see myself thinking that this was a good plan.
