At 4:50 a.m. on Sunday, September 3, 1967, every motor vehicle still permitted on Sweden’s roads was ordered to stop. Drivers brought their vehicles to a halt on the left side of the road, waited briefly, crossed carefully to the right, and stopped again.

At precisely 5:00 a.m., they were allowed to proceed. In the space of ten minutes, Sweden had changed which side of the road an entire country drove on.

This was not a limited experiment involving three unusually cooperative villages and a traffic cone. Every road in Sweden had switched from left-hand to right-hand traffic. The event was called Dagen H—something that sounds suspiciously like a lactose-free version of fancy ice cream. In reality, it meant “H Day,” with the H standing for högertrafik, or right-hand traffic.

The change itself took ten minutes. Making those ten minutes possible took four years, more than 600 million Swedish kronor, hundreds of thousands of road signs, thousands of rebuilt buses, a hit song, and at least one piece of historically significant underwear.

Sweden Had Already Changed Sides Once

Right-hand traffic was not entirely new to Sweden. In 1718, King Charles XII issued a regulation requiring postal carriages meeting on the road to keep to the right. Sweden abandoned that rule in 1734 and began keeping to the left instead.

For much of the next two centuries, left-hand traffic continued as a matter of law, local regulation, or simple habit. A 1923 traffic ordinance finally established it for every category of road user throughout the country.

Consequently, the 1967 switch was not so much Sweden trying right-hand traffic for the first time as ending a 233-year experiment with the other answer. This was not even the country’s first experience with a baffling nationwide correction. Sweden had previously managed to produce February 30, 1712, while attempting to fix its calendar. The Swedes seem perfectly normal most of the time, but every few centuries they apparently feel compelled to make everyone check which day it is and where they are supposed to stand.

The Wrong Cars for Left-Hand Traffic

Left-hand traffic had become increasingly inconvenient. Sweden’s neighbors—Norway, Finland, and Denmark—drove on the right, as did nearly all of continental Europe. Every international road trip therefore included a moment when drivers had to cross from one side of the road to the other and trust that everyone involved had received the same instructions.

We have previously looked at why different countries drive on different sides of the road. The short answer is that history, horse traffic, military traditions, and national stubbornness produced two incompatible systems, after which automobiles arrived and made the disagreement much faster.

Sweden had an additional problem: most Swedish cars already had their steering wheels on the left. That arrangement makes sense when driving on the right because it places the driver near the center line. Under Sweden’s left-hand system, however, the driver sat near the roadside, making it harder to see around a vehicle before overtaking it.

In other words, Sweden had left-hand roads, right-hand neighbors, and cars designed primarily for right-hand traffic. The country had somehow assembled every component of a workable traffic system while arranging them in the least cooperative order.

The parliamentary decision applied to road and street traffic, as well as trams. It did not apply to railways or the Stockholm subway, which continued operating on the left. Even a nationwide reversal came with terms and conditions.

Swedish Voters Say No—Very Clearly

Government officials had discussed switching sides for decades, but Swedish motorists were not enthusiastic. In 1955, the country held a national referendum on the question. The public response did not leave much room for imaginative interpretation.

Of the 2,581,687 votes cast, 2,139,996 favored retaining left-hand traffic. That was 82.9 percent of the vote. Only 400,061 voters—15.5 percent—supported changing to the right, while 41,630 submitted blank ballots, presumably because even traffic policy deserves a small constituency committed to voting and driving in the middle of the road.

Turnout was about 53 percent, and the referendum was advisory rather than legally binding. Parliament initially followed the voters’ recommendation and retained left-hand traffic. The result was nevertheless about as decisive as referendums get without adding a second question asking, “Seriously, what part of ‘no’ was unclear?”

Parliament Changes Direction

During the next several years, international traffic continued to increase. The Council of Europe encouraged uniform traffic rules, the Nordic Council urged Sweden to act, and the safety problem created by left-hand-drive cars on left-hand roads did not become less peculiar with age.

On May 10, 1963, the Swedish Parliament approved the change to right-hand traffic by a vote of 294–50. The government’s formal proposal to Parliament emphasized the growth of international road traffic and the advantages of following the same rule as Sweden’s neighbors. The referendum had not become binding during the intervening eight years, nor had the voters obviously awakened one morning and decided they had been too hasty. Parliament simply concluded that the practical arguments for changing sides outweighed the public’s exceptionally well-documented preference not to.

Legally, this was not the government defying a binding popular vote. It was Parliament reversing course after an advisory one. That distinction is constitutionally meaningful, although probably less comforting when 82.9 percent of the voters have just explained that they would prefer you not do the thing you are preparing to do.

The official estimate placed the cost at 400 million kronor, and the final figure exceeded 600 million—roughly 5.5 to 7.6 billion kronor today, or about $570 million to $790 million. Sweden was not merely changing lanes; it was funding the modern equivalent of a major national infrastructure project.

Four Years of Preparation for Ten Minutes of Movement

The government created the Swedish Right-Hand Traffic Commission to oversee the conversion. Its work included engineering, legislation, vehicle modification, public education, traffic safety, psychology, and mass communication. Changing sides was not simply a matter of telling drivers, “Starting Sunday, do the opposite.”

Intersections had to be redesigned. Bus stops had to be moved to the other side of the street. Traffic lights, one-way systems, road markings, highway entrances, pedestrian routes, and turning lanes all had to be reconsidered. Approximately 360,000 road signs were replaced, and another 130,000 special reminder signs were installed.

The new signs were erected in advance and covered until Dagen H. During the final night, about 20,000 workers moved, uncovered, or concealed roughly 300,000 signs. It was the highway equivalent of setting up an enormous surprise party, except the surprise was that every familiar instruction had moved across the road.

Buses created one of the largest expenses. A bus designed for left-hand traffic opened its passenger doors toward the left curb. After the switch, those same doors would open into moving traffic, adding an unfortunate second stage to the morning commute. Approximately 8,000 buses had to be rebuilt or replaced.

Roadside life also had to move. Archival histories report that hundreds of thousands of rural mailboxes and milk-collection stands were relocated. Even the elk-hunting season was brought forward by a week so hunters would not add to traffic during the changeover. Apparently the planners had reached the point where “What about the elk hunters?” was no longer an absurd question but an item requiring a subcommittee.

The Campaign to Rebuild the Swedish Driver

Rebuilding intersections was comparatively straightforward. The more difficult task was rebuilding several million habits.

The commission concluded that reaching 90 percent of the public would not be good enough. Anyone who could independently enter traffic had to know when the change would occur and what to do afterward. Officials therefore arranged home visits for isolated, elderly, ill, and disabled people. Special information was prepared for blind and deaf residents and for people who did not speak Swedish. Materials at border crossings appeared in multiple languages.

Yes, we know some of you are wondering why people who were blind needed special instructions when they were not the ones changing lanes behind the wheel. The answer is that Dagen H changed life for pedestrians too. They had to relearn which direction traffic would approach from when crossing a street and where buses would now stop. As we have said, switching sides affected considerably more than which half of the pavement contained the cars. It rearranged many of the assumptions people relied on simply to move through everyday life.

Radio and television had been preparing audiences for more than a year, but the campaign deliberately avoided explaining precisely how to behave in right-hand traffic until August 30—just four days before the switch. Experts feared that teaching the new behavior too soon might create two competing sets of habits and cause people to start practicing right-hand driving while the country was still officially keeping left.

This produced the unusual educational strategy of telling everyone for months that an important change was coming while withholding some of the practical instructions until immediately before it arrived. Anyone who has ever assembled furniture using directions found underneath the completed bookcase will recognize the general approach.

During the final weekend, Swedish television broadcast about 12 hours of right-traffic programming. Radio carried approximately 40 hours across three channels and ten languages. A national song competition produced “Håll dej till höger, Svensson”—“Keep to the Right, Svensson”—which turned traffic safety into something disturbingly close to a pop hit.

The Right-Hand Traffic Underwear Was Real

The blue-and-white Dagen H logo appeared on newspapers, milk cartons, shopping bags, stamps, gloves, dashboard stickers, and countless other objects. A Swede could eat breakfast, collect the mail, go shopping, turn on the radio, or get into the car without being allowed to forget which side of the road would become correct on September 3.

The campaign also inspired right-hand-traffic-themed underwear. It appears to have been commercial merchandise inspired by the campaign, not an official government-issued traffic-control device. Sweden did not, so far as the surviving records indicate, establish a Department of Corrective Lingerie.

Nevertheless, if the purpose of a public-information campaign is to put its message where citizens cannot avoid seeing it, the Swedes had clearly reached a part of the advertising market normally overlooked by highway departments.

At 4:50 a.m., Sweden Stops

The nationwide driving restrictions began at 1:00 a.m. on September 3. Ordinary motor traffic was prohibited until 6:00 a.m., with longer closures in parts of Stockholm, Gothenburg, and several other cities. Only buses, taxis, emergency vehicles, specially exempted vehicles, and traffic connected with the conversion itself could remain on the roads.

That detail is important. Sweden did not place every driver in the country on the highway at the same moment and hope national character would take care of the rest. The ten-minute maneuver involved only the limited traffic still authorized to operate.

The government’s official household guide to Dagen H gave precise instructions. At 4:50, drivers were to stop on the left. After a short pause, they were to cross carefully to the right and wait there until 5:00. The interval could also be used to adjust or uncover headlights that had been modified for the new traffic direction.

More than 100,000 volunteer traffic guides were stationed at thousands of intersections, supported by police and military personnel. Temporary speed limits reduced traffic to 40 kilometers per hour in most urban areas, 60 on ordinary rural roads, and 90 on motorways. Drivers were also required to use their headlights.

At 5:00, the radio signal came. The waiting vehicles began moving forward on the right. At 6:00, most of the general public was allowed to join them.

The Famous Photograph Looks Worse Than It Was

The best-known photographs of Dagen H show Stockholm streets packed with vehicles apparently moving in every possible direction at once. One especially famous image from Kungsgatan looks less like an orderly transition than an attempt to demonstrate traffic using a bowl of spaghetti.

There was some genuine confusion there. Large crowds had gathered to watch the switch, taxis had assembled in anticipation, and the intersection briefly became tangled. Order was soon restored, however, and the scene was not representative of the country as a whole. A completely uneventful rural intersection may be better evidence of successful planning, but it rarely becomes an iconic photograph.

A contemporary newspaper account preserved by The Guardian described occasional traffic jams and minor accidents but praised the extraordinary attention to detail. The massive nationwide breakdown that opponents feared simply did not materialize.

The Automotive Apocalypse Fails to Arrive

Contemporary reports counted 157 traffic accidents on Dagen H, with 32 involving personal injuries and only a small number considered serious. The following Monday produced 125 reported accidents, below the usual Monday range of 130 to 198.

Instead of producing the predicted bloodbath, the change was followed by an immediate reduction in accidents. Drivers were intensely aware that every familiar habit had become potentially dangerous, so they slowed down, watched one another, and approached intersections as if everyone else might suddenly remember the old rules.

The temporary speed limits, heavy enforcement, reduced traffic, publicity campaign, and other safety reforms also mattered. It is therefore too simple to say that moving to the right automatically made Sweden safer. The initial improvement gradually faded as drivers became comfortable with the new system and rediscovered the confidence necessary to make poor decisions at normal speed.

Official figures recorded 236 fewer traffic deaths in 1967 than in 1966. It is tempting to award all of them to Dagen H, but the switch occurred in September, and several other traffic laws changed at about the same time. Arithmetic has entered an objection, and the objection is sustained.

Sweden Did Not Really Change Sides in Ten Minutes

Dagen H is often remembered as the morning Sweden reversed its traffic in ten minutes. That is accurate in the same way a theatrical performance lasts two hours while politely omitting the rehearsals, construction, lighting, costumes, and nervous breakdowns required to make those two hours possible.

The switch succeeded because Sweden did not treat it as a simple instruction. Officials redesigned the roads, changed the vehicles, altered the laws, restricted traffic, lowered speeds, recruited guides, studied human behavior, and placed reminders virtually everywhere a reminder could reasonably—or unreasonably—be placed.

At 4:50 a.m., the country pressed pause. Ten minutes later, it pressed play with every road running in the opposite direction. The feared national traffic disaster missed its appointment.

Sweden changed sides in ten minutes. It merely took four years, 360,000 road signs, 8,000 buses, more than 100,000 volunteers, a hit song, and one historically overqualified pair of underwear to make those ten minutes possible.

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