On 3 September 1967, Sweden switched from driving on the left to driving on the right, says The Guardian. “Höger-dag”, or “Right Day”, was four years in the planning. A small army of construction workers worked overnight to make the final alterations to the country’s 350,000 street signs, and on hand to help drivers were 2,000 soldiers, 6,000 civil police, 50,000 school police, and 150,000 volunteers. The change itself took place at 5am. It prompted complete chaos in the centre of Stockholm, with vehicles “getting hopelessly entangled” as they tried to switch over. But the rest of the day went smoothly, with only “the occasional jam and a number of minor accidents”.