"Dagen H," or "H Day," refers to the day when Sweden switched from driving on the left side of the road to the right. This significant change took place on September 3, 1967, and aimed to improve road safety and align with neighboring countries. The letter "H" stands for "höger," which means "right" in Swedish. The transition involved extensive public education campaigns and logistical planning to ensure a smooth changeover. On that day, traffic was halted for a brief period to allow for the switch, and signs were updated to reflect the new driving rules. The event is often remembered as a major milestone in Sweden's transportation history.