It was a normal Sunday in September 1967 in Sweden, except that every driver on the road was about to have to change the way he or she did things. At 5 a.m., traffic switched from driving on the left-hand side of the road to the right. And a bit of mayhem ensued, what Time Magazine called a “brief but monumental” traffic jam.

(Jan Collsiöö/public domain)

Now known as “Dagen H Day” — Dagen means “day,” and the “H” stands for “Högertrafik,” the Swedish word for “right-hand traffic” — the story was mostly forgotten until the photo resurfaced on social news site reddit Friday. It generated hundreds of comments.

Sweden initiated the driving change in part because its neighbors already drove on the right side of the road. Many members of the Swedish parliament also argued that the left-hand vehicles Swedes drove had caused too many head-on collisions. “Do you want to see your mother killed?” one politician dramatically said, arguing in favor of the change.

The country’s citizens, however, were not convinced. In 1955, a national referendum found that more than 80 percent of Swedes opposed the driving change, according to Volvo. So a national campaign of persuasion was begun, and the Dagen H logo was soon emblazoned on milk cartons, shorts and even women’s underwear.

On the day of the change, only 150 minor accidents were reported. Traffic accidents over the next few months went down. The politicians seemed to have been right.

By 1969, however, accidents were back at normal levels. The debate over the sageness of the decision was revived.

Now, 45 years later, thanks to the Internet’s habit of rediscovering historical treasures, that debate rages on.