In 1967 Sweden switched, overnight, from driving on the left to driving on the right, stopping almost all traffic in the entire nation at a set hour so that every car, bus and lorry could cross to the other side of the road at once, in what remains one of the largest coordinated logistical events a country has ever attempted.

At 4:50 in the morning on Sunday 3 September 1967, every single vehicle on every single road in Sweden came to a complete stop. There were, at that point, roughly 1.97 million registered vehicles in the country. Their drivers had been informed for months, through a public awareness campaign that had reached practically every household in the nation, that at exactly this moment they would need to pull over onto the verge of whatever road they happened to be on, wait for ten minutes without moving, and then, at exactly 5 o’clock, cautiously ease themselves across the centreline onto the opposite side of the road and continue their journey there. For the previous 233 years, Sweden had driven on the left. From 5 o’clock that Sunday morning onwards, forever afterwards, Sweden would drive on the right. There was no gradual transition. No parallel systems. No trial period. Every driver in the country made the switch at exactly the same moment, on national radio countdown, and the operation had a name. It was called Dagen H, for Högertrafikomläggningen, which is Swedish for “the right-hand traffic reorganisation,” or, more loosely, “H-Day.”

Why they decided to do it in the first place

Sweden had been the last remaining left-hand-driving country in mainland Europe by the 1950s. Every one of its immediate neighbours drove on the right. Crossing from Sweden into Norway or Finland involved a mandatory sides-switch at the border, which was an obvious source of confusion and accidents at any hour of the day. Even more awkwardly, the majority of cars actually being driven in Sweden were left-hand-drive vehicles, meaning that the driver sat on the left side of the vehicle rather than the right. This was because in the early decades of the twentieth century most cars sold in Sweden had been imported from the United States, where left-hand-drive was standard. By the 1960s even domestically-produced cars from Volvo and Saab were being built as left-hand-drive to match what most Swedish drivers were used to and what the export market required. The practical consequence was that on any Swedish road, the driver of a typical car sat on the side of the vehicle furthest from the oncoming traffic, which made overtaking a slow-moving vehicle in front of them a matter of guesswork and prayer.

The Swedish government had been aware of the problem for decades. According to Brendan McAleer’s 2022 history of Dagen H for Hagerty Media, drawing on Swedish government records and contemporary reporting, a public referendum on the question had been held in 1955, asking Swedish voters whether they would prefer to keep driving on the left or switch to the right to match the rest of continental Europe. The result was overwhelming. Roughly 83 per cent of Swedish voters said they preferred to keep driving on the left. Their reasoning, insofar as anyone bothered to canvas it, was a combination of expected cost (many hundreds of millions of kronor in signage, roadworks, and public education), general suspicion of governmental change, and the specific fear of what the transition day itself might bring in terms of mass carnage on the roads. The Swedish parliament, the Riksdag, considered the referendum result carefully, and then in May 1963 decided to go ahead with the switch anyway. Four years of preparation followed. The switch date was set for September 1967.

How the actual day played out

The preparation was extraordinarily thorough. Every intersection in the country had to be physically reconfigured. Traffic signs were replaced or repainted. Road markings were repainted. Buses had their doors moved from the left side to the right side of the vehicle, and thousands of new right-hand-door buses were purchased outright to replace those that could not be modified. Traffic lights were reinstalled to face the correct direction. According to Popular Science’s 2026 account of Dagen H by writer Leah Hudson, drawing on the research of Dr. Felix Rösel of Technische Universität Braunschweig and Dr. Christina Rudin-Brown of Human Factors North, the public education campaign that ran alongside the physical preparation was equally comprehensive. A Dagen H logo was designed, a leaning yellow letter H on a blue background, and appeared on milk cartons, coffee cups, soda bottles, socks, underwear, and shopping bags across the country in the months leading up to the switch. Every household in Sweden received a 32-page instruction pamphlet, printed in nine languages to accommodate immigrant residents. Children were taught the new rules through cartoons featuring Donald Duck and Dennis the Menace. A pop song called “Håll dej till höger, Svensson” (“Keep to the right, Svensson”) was commissioned specifically to help drivers remember the change, and it reached number five on the Swedish music charts, staying in the top ten for three weeks.

On the Saturday before the switch, most non-essential traffic was banned nationwide. In Stockholm and Malmö, the ban actually began at 10 o’clock Saturday morning and ran until 3 o’clock on Sunday afternoon, to give the work crews enough uninterrupted time to reconfigure the more complicated urban intersections. In the rest of the country, the ban ran from 1am to 6am on the Sunday morning. The 4:50 stop and the 5:00 restart applied to every vehicle that was allowed on the road during those five hours. The mood, according to contemporary reports collected by both Hagerty and Popular Science, was less one of anxiety than of national festival. Crowds began gathering on major streets in Stockholm at around 4am. Fireworks were set off. Impromptu choirs formed and sang the “Keep to the right, Svensson” song. Every taxi driver in the city seemed to have come out to be part of the moment. One man, who had apparently been unable to sleep from the excitement, turned up on Kungsgatan in his pyjamas. At the appointed moment, the cars stopped. They waited. Ten minutes passed. Then, on the radio countdown, they began, in slow careful coordinated motion, to move from the left side of the road to the right, and continue driving on the opposite side of where they had been driving for the previous two centuries and change.

The immediate results exceeded even the government’s optimistic projections. On the Sunday of Dagen H itself, only 157 minor accidents were reported nationwide, and none of them were fatal. On the Monday after, there were 125 reported traffic accidents across the entire country, which was actually below the typical range of 130 to 198 for previous Mondays, and again, none of them were fatal. Throughout the following weeks, accident rates remained substantially below their pre-Dagen H baseline, partly because drivers were being unusually cautious and partly because new lower speed limits had been introduced alongside the switch. According to the Rösel study cited by Popular Science, the total number of traffic deaths in Sweden in 1967 was 1,077, down from 1,313 in 1965, and Rösel’s subsequent analysis calculated that if the switch had been made earlier in the twentieth century, more than 4,000 additional Swedish lives could have been saved between 1953 and 1966 through the corresponding reduction in wrong-side driver misalignment accidents. The public opinion figures shifted with the outcome. The 83 per cent who had voted against the change in 1955 shrank to something under half within weeks of the actual event, and by the end of the year, 57 per cent of Swedes were describing the switch favourably. Nobody has proposed changing it back.