Margen
Sweden drove on the left, like the United Kingdom, but with an added quirk: almost all its cars had the steering wheel on the left, and its neighbours — Norway, Finland, Denmark — drove on the right. Every border crossing and every overtake was a trap.
The fix was put to a referendum in 1955, and 83% said no. Parliament decided to do it anyway and set the date: 3 September 1967, christened Dagen H.
Preparations took years: some 360,000 road signs were replaced, junctions and buses were redesigned, and the campaign reached absolutely everyone — there was even a song contest to drum it in ('Keep to the right, Svensson' played on the radio).
In the early hours of H-Day, non-essential traffic was banned. At 4:50 a.m., every vehicle in the country stopped where it was, moved carefully across to the right-hand side of the road, and waited. At 5:00, they set off again.
The predicted chaos? Quite the opposite: that Monday saw fewer accidents than an ordinary Monday, and insurers recorded weeks of record lows. Driving had suddenly become so strange that the whole country did it as if sitting the test: slowly, both hands on the wheel.