Dagen H (H day), today usually called “Högertrafikomläggningen” (“The right-hand traffic diversion”), was the day on 3 September 1967, in which the traffic in Sweden switched from driving on the left-hand side of the road to the right. The “H” stands for “Högertrafik”, the Swedish word for “right traffic”. It was by far the largest logistical event in Sweden’s history.
However, the change was unpopular; in a 1955 referendum, 83 per cent voted to keep driving on the left
A non-binding referendum on the introduction of right-hand traffic was held in Sweden on 16 October 1955.
The voter turnout was 53.2%, and the suggestion failed by 15.5% against 82.9%. However, eight years later, in 1963, the Riksdag approved the change, following pressure from the Council of Europe and the Nordic Council. Traffic in Sweden switched from driving on the left-hand side of the road to the right on 3 September 1967 (see Dagen H).