In Sweden in 1967 it was known as Dagen H. In Iceland in 1968 it was known as H-dagurinn. What was it?

These terms refer to when drivers in Sweden and Iceland changed from driving on the left side of the road to the right side of the road.

https://en.wikipedia.org/wiki/Dagen_H

https://en.wikipedia.org/wiki/H-dagurinn

At least in Sweden, people were highly sceptical and afraid of this historic change. Polls before Dagen H showed that over 80% of the population opposed the switch.

Drivers became exceptionally cautious because everyone was so terrified. This fear actually worked as a safety mechanism. On the day of the changeover, accident rates plummeted and not a single fatal accident was recorded.

Here's a report:

https://www.youtube.com/watch?v=yiInZNG2dhk