Right-side driving was debated in the Swedish Parliament for a number years, with proponents suggesting that Sweden should adopt the same side of the road as their Scandinavian neighbors. Others thought it would be dangerous to make such a radical change. A referendum was put before the Swedish people in 1955 and they overwhelmingly chose to stay left.
As governments are wont to do occasionally, the will of the voter was ignored and parliament passed a law in 1963 mandating right-side driving beginning September 3, 1967.
Over the nighttime hours of September 2 & 3, signs all over Sweden were changed to accommodate the new driving law. At 4:50AM, traffic nationwide was stopped and vehicles were directed to the right side of the road. At 5:00AM, traffic was again allowed to move but at a very reduced speed.
The photos posted here are from the excellent Retronaut Web site. They depict the moments leading up to the national changeover. The photos show a large police presence along with more than a few tow trucks, probably standing by to move cars that could not be moved on their own. Of course spectators and photographers are in abundance as well.