As well as the fact that their neighbours drove on the right, the argument was made that switching sides would reduce accidents due to Swedes mostly owning left

As well as the fact that their neighbours drove on the right, the argument was made that switching sides would reduce accidents due to Swedes mostly owning left-hand drive cars. There were fewer accidents initially, but things returned to historic levels pretty soon thereafter: https://en.wikipedia.org/wiki/Dagen_H https://en.wikipedia.org/wiki/Dagen_H