In 1967, Sweden switched from driving on the left to the right — in 10 minutes.

Cars changing lanes on Dagen H

At 4:50 a.m. on September 3, 1967, every active motorist in Sweden, driving on the traditional left side of the road, suddenly pulled to a stop. Ten minutes later, at 5 o’clock sharp, the train of cars began carefully navigating across the center lines to resume driving on the right side. “Högertrafikomläggningen” (“the right-hand traffic diversion”), also known simply as “Dagen H” (“H-Day”), had officially begun.

There were several factors that prompted the Swedes to undertake this monumental adjustment, including the fact that most of the rest of Europe was driving on the right side of the road, and most cars within Sweden were already built for right-side driving with their steering wheels on the left. And so, Parliament voted to move ahead with the switch in 1963.

Officials took four years to carefully prepare for H-Day: Traffic lights and bus stops were reinstalled, intersections and bicycle lanes were redesigned, and a massive information campaign warned citizens of the big shift to come. The only suddenness of the situation came with the alteration of the nation’s 360,000 road signs, which largely took place in the 24 hours leading up to the event.

While it’s logical to assume that the switcheroo resulted in a series of unfortunate traffic events, the opposite was true, as thousands of police and military personnel proliferated the streets during the transition to guide wayward motorists and ensure strict speed limits were kept. The number of minor traffic accidents reported on the first Monday after the event was down slightly from the national average, while the number of traffic-related injuries from 1967 was also lower than in previous years, all of which promised that H-Day would be remembered as a success.

By the Numbers

Did you know?

Many right-side or left-side traffic customs predate the existence of cars.

Why is it that some countries funnel vehicle traffic down the right side of a road while others take it to the left? According to historian M.G. Lay, author of Ways of the World, these rules often stem from old traditions that predate the existence of cars. Japan’s preference for the left side of the road, for example, is said to originate in the practice of avoiding the accidental clashing of swords among foot travelers, while in England, solo horse riders and small carriage drivers bore left so as to keep their right hand available for greeting or attacking, if needed. On the other hand, the popularity of Conestoga wagons in the British colonies in America, which often saw drivers walking on the left side of horse teams to control the animals with their dominant right hands, led to the development of road rules that coded right-side traveling into American legislation. Meanwhile, regulations enacted during France’s revolutionary period dictated traffic flow on the right, a habit reinforced throughout much of Europe thanks to the conquests of Napoleon.