In Sweden, the 1967 change from left-hand to right-hand driving was called Dagen H.
The switch took place on 3 September 1967. The letter H referred to “Högertrafik,” the Swedish term for right-hand traffic. At the appointed time, vehicles stopped or moved carefully into the new right-side pattern under a tightly coordinated national plan.
Sweden made the change because most neighbouring countries already drove on the right. The old arrangement created practical problems for cross-border travel and vehicles designed for surrounding traffic systems. A nationwide information campaign prepared drivers for the change, including new signs, road markings and temporary restrictions.
Dagen H is often mistaken for a simple change in lane markings, but it required a complete traffic-system conversion. Vehicles, intersections, signs, public transport operations and driver behaviour all had to be adapted simultaneously.