Back in 1995, Tingvall had become the head of road safety for the Swedish Road Adminstration. He was very well qualified for the role, but quite unlike any of his predecessors. Instead of coming up through the ranks of road transport engineers and bureaucrats, Tingvall had a medical background: he had studied at the renowned Karolinska Institute, where he had gained a doctorate in the epidemiology of injuries.

In the 1990s, the road safety world was focused on technological measures such as seatbelts, car seats for children and airbags. These measures softened the impact of what is sometimes called "the second collision" in car crashes – the impact of passengers within a vehicle, moments after a crash has occurred. (Less attention was given to injuries sustained by road users who had the misfortune to be outside the vehicle.)

Tingvall knew that this approach didn't go far enough. "The car can't solve everything, because it doesn't work like that," he says. "You bottom out the safety net of the vehicle."

He saw that injuries were a result of combining a speeding mass with the built environment and many other variables, including road conditions and the driver's behaviour, as well as the safety features on the vehicle.

This "systems" approach wasn't new to road safety experts, but it differed from the way officials looked at road collisions, which was primarily through a criminal justice lens.

After the crash near Stockholm, Tingvall called the regional director of the transport authority to his office in Borlänge, about 220km (137 miles) away from the capital. He asked the official what he planned to do following the incident. The reply stated the authority would swiftly replace the concrete lamppost.

But Tingvall demanded that all such supports be removed, since they were clearly a hazardous feature to have right next to a road. Work began to improve Sweden's "clear zones" next to roads, but it caused disquiet among officials. Wasn't changing the road layout tantamount to admitting liability for the crash?

Tingvall did indeed believe that the authorities were responsible – not for reckless driving, or for the crash itself – but for the fact that the incident was as fatal as it was. And within a couple of years, Swedish parliamentarians would align themselves with this way of viewing road safety.

"They said: 'You as provider of the road transport system are no longer allowed to kill people on that mass level that you've done'," Tingvall recalls. Globally, he estimates that at least 100 million people have died on the roads since the birth of the motor car.

Road transport developed in relative freedom, outside the control of a safety culture that put the preservation of life beyond all other values.

This sets it apart from other modes of transport. Passengers travelling by train, boat or plane have high expectations of safety. Of course, accidents do occur, but stringent protocols mean these are relatively rare events. Even for dangerous jobs like construction work or oil drilling, safety is of paramount value. Workers are kept safe by a mix of training, protocols and equipment, planned by experts in recognition of the risky nature of the work.  

But from a very early point in the development of the motor car, the industry decided to focus the attention of lawmakers away from the inherent dangerousness of cars to the actions of the person behind the wheel.

From the 1930s, the Automotive Safety Foundation (ASF) – a US body created in 1937 that was backed and controlled by car manufacturers until it was merged into the Highway Users Federation in 1970 – sponsored films, posters and TV items about the importance of driving responsibly, and they lobbied for driving tests.

"There was a lot of blame directed at the driver, and they were quite willing to go after reckless drivers aggressively because they were a threat to the reputation of the industry," says Peter Norton, a historian at the University of Virginia and author of Fighting Traffic: The Dawn of the Motor Age in the American City. "Traffic enforcement principles were really developed by the auto industry themselves directly. They sponsored traffic enforcement training for police officers."

Norton has found that the ASF paid for a traffic enforcement programme at Northwestern University, which trained students from across the US. They also paid to establish the Traffic Division of the International Association of Chiefs of Police, which advised police forces on traffic enforcement.

But bad drivers weren't the only target of car manufacturers – pedestrians were often involved in crashes too, so they lobbied for the development of highways that excluded them (but which also encouraged people to drive faster).

The resulting idea that still persists today to some degree could be considered as analogous to the infamous slogan from the National Rifle Association of America: Cars don't kill people, people do.

That outlook is changing though. While the US is lagging behind Europe and Australia in improving road safety, there is increasingly a "safe-systems approach" inspired by strategies such as Vision Zero, says Bruce Hamilton, executive director of the Roadway Safety Foundation, a road safety charity that is one of two successor organisations from the ASF. "We have more than four million miles (6.4 million km) of roads here in the US, so we have a lot of work to do," he says. He says the car-centric approach to road safety that dominated car, city and street design for decades and the focus on regulating driver behaviour is changing in favour of redesigning and upgrading road infrastructure.

There are significant challenges though. "Half of our road fatalities occur on rural roads in the US," Hamilton says, which means ensuring adequate funding to address safety problems can be difficult.

With individual road users carrying the moral and legal weight of road crashes, officials at transport authorities were free to prioritise other things. When Tingvall joined the Swedish road authority in 1995 he was expected to balance road safety with other variables, including cost, driver preference and the impact on the economy of changing traffic flows.

The real moment of change, he believes, came some months before the crash south of Stockholm, when a conversation took place in his office. It was during a visit from Ines Uusmann, the minister for infrastructure, and Tingvall's political boss. At one point she turned to him and asked, simply: "How many deaths should we have as our long-term target in Sweden?"

Tingvall replied: "Zero." To his surprise, Uusmann said she was interested and would like to hear more. This was the beginning of an approach to road safety known as "Vision Zero".

Uusmann, who had a background in the Trade Union movement, was familiar with the principles of workplace safety. With her support, Vision Zero quickly gained traction. Aiming for zero road deaths seemed to many – and still does seem to many – to be utopian and unrealistic. But for Tingvall, the target is an inevitable consequence of an authority taking back responsibility for road safety from individual drivers. He believed they had a moral duty to aim for zero.

On 22 May 1997, the Swedish government presented Bill 1996/97:137 to parliament. It cemented zero deaths as a long-term goal for road fatalities. It reiterated that transport designers were responsible for maintaining the road system, while drivers were expected to drive responsibly and follow the rules. However, a further clause stated that:

"If the road users do not adequately assume their share of the responsibility, for example, due to a lack of knowledge or skill, or if personal injuries occur or risk occurring for other reasons, the system designers must take additional further measures to prevent people being killed or seriously injured."

This meant that officials were no longer allowed to design roads for idealised drivers who never became distracted or exceeded the speed limit. They had to make roads for real people who made mistakes.

As Tingvall puts it: "It should be up to the professional community to make sure that that normal people, doing normal mistakes, don't lead to them killing themselves or someone else."

Even intentional law-breaking was to be considered when designing the system. The reality is that drivers do speed, and they get distracted by their phones or other passengers in the car. "Don't pretend that there are laws that you know everyone will follow," Tingvall says. "That's very unprofessional. You would never do that in aviation or in other areas where you really care for safety."

One of the key actions that came from Vision Zero was to conduct internal investigations of every fatal road collision in Sweden in parallel to any criminal investigation. The pattern that began to emerge revealed that crash victims were not, as many in the road transport sector, assumed – drunk and irresponsible drivers. For the most part, they were people who made small mistakes within a system that had no margin for error.

Tingvall did not develop Vision Zero alone, but alongside many like-minded individuals from diverse backgrounds. From the Karolinska Institute he worked alongside Anders Lie, an expert in reconstructing crashes from photographs, Anders Kullgren, an engineer, and Maria Krafft, who is Sweden's head of road safety today. Tingvall still works closely with all three.

To underline the shift in thinking, Tingvall commissioned the artist Karl Jilg to create a series of strange illustrations, which were used in presentations about Vision Zero. They showed everyday scenes, but with the risks of horizontal kinetic energy – i.e. speed – transposed to height. The resulting effect showed pedestrians walking along pavements and crossings next to dizzying precipitous drops.

After decades of government campaigns that aimed to change driver behaviour, the pictures came as a shock. They didn't depict dangerous drivers – one pair of images didn't show drivers at all – but a network of roads that seemed to pose an inherent risk to people going about their everyday lives.  The onus fell to transport planners – not drivers – to fix that situation.

In 1998, things were going well for Tingvall – but then he tried to actually change the roads. 

There was a notorious section of the E4 highway north of the city of Gävle, in which 21 people had lost their lives in the previous eight years. The reason was head-on collisions, caused by drivers who fell asleep at the wheel, or lost control of their cars in dangerous conditions, drifting across the road.

Tingvall proposed using this section to trial a median barrier made of wire rope. Cars would still be able to overtake on sections where a second lane became available – a so-called "2+1" road.

The road safety community was deeply sceptical. Why would anyone put obstacles in the middle of a road? Surely that would lead to more crashes.

"People said: 'You must be stupid because people are going to crash into that barrier,'" recalls Tingvall. "And I said: 'Yes, I know. That's the idea.'"

The National Society for Road Safety thought the trial was "horrendous" and an editorial opposing the plans appeared in a respected national newspaper. Tingvall conducted a consultation with residents living near the road – 0.3% said they thought it was a good idea. Nevertheless, he persisted with the trial.

"After a few weeks we had the first crashes," he recalls. "They went well, if I can call it that. We even had a cake sent to us." This unexpected gift came from a woman who said she owed her life to the new barrier. She had been distracted in the car by her sick dog, and had swung into the middle of the road, hitting the barrier instead of the oncoming traffic.

Tingvall was surprised by the cake, but not by the results of the trial. His scientific work had told him that even if the number of crashes increased because of the barrier, they would be much less deadly. (The barriers are more problematic for motorcyclists, though Tingvall says research suggests there is still a net safety benefit.)

Within six months of the trial on the E4, the Swedish Transport Administration found that the majority of the Swedish public said they wanted median barriers on their roads, and they began to quickly spread through the country's rural road network. Research has shown that after they were installed, 2+1 roads cut the number of people killed and seriously injured by half. Tingvall believes they have saved more than 1,000 lives.

This effort to focus on the deadliest types of crashes led Tingvall to borrow the roundabout – also known in the US as a rotary – from the UK. They are now a common sight in Scandinavia. Collisions are more common on roundabouts than intersections, but they are much less deadly, because cars move slowly and in the same general direction.

Tingvall didn't just look at road layouts. "In 1995, motor journalists looked at cars and said, 'It feels solid – it's probably safe as well,'" he recalls. The following year, the Swedish Transport Authority helped create – together with the UK – a voluntary rating system for cars, to show consumers which models were safest.

The European New Car Assessment Programme (Euro NCAP) received support from governments and motoring associations, but manufacturers were resistant. However, when a Volvo model emerged from the tests as the safest, the accolade became a cornerstone of the company's marketing, and the industry woke up to the importance of safety for drivers.

Tingvall took Vision Zero to Australia in 1998, where it was renamed the "safe system" approach. In 2002, it was formally adopted by Sweden's neighbour Norway, while at the municipal level Vision Zero has been implemented in dozens of cities around the world, from Barcelona to Bogota.

In 2011 it was adopted as part of the EU's road safety strategy. In the following decade, deaths on European roads fell by about one third, while in the US deaths went up, even when accounting for changes in population size.

It should be noted that European road deaths were already declining prior to 1995, and some of the recent gains would probably have happened without Vision Zero. Moreover, because Vision Zero describes a mindset and a method – rather than a to-do list of actions – it's hard to say where it begins and ends.

Swedes still associate the term with those median road barriers, but almost any safety intervention could fall within a Vision Zero plan, so long as it is evidence-based. Norway has 179 actions on its current Vision Zero plan – they range from installing median barriers on 435 km (270 miles) of national roads to promoting first aid training for the public.

And while Vision Zero looks at more than just the actions of the person behind the wheel, dangerous drivers are not let off the hook: in Spain, Vision Zero initiatives include cracking down on drink driving, while in south-west England, the public are invited to submit videos of reckless law-breakers. Meanwhile in cities, Vision Zero is most often associated with measures to protect pedestrians and cyclists.

Tingvall admits that this was an area that his team came to rather late. The segregated cycle ways and low-traffic neighbourhoods now found in cities like London, Brussels and Seville are influenced by a Dutch approach to urban design that begins with classifying the functions of different roads. This model, "Sustainable Safety", developed alongside Vision Zero and in time the two approaches grew closer together.

More than 50 US cities have also signed up to Vision Zero, though the measures sometimes differ from their European counterparts. "It's very easy to say that you stand for Vision Zero," says Norton. "The hard part is getting the measures that make Vision Zero matter."

Twenty-mile-an-hour speed limits and automated speed cameras are rare in the US, and, as a recent review found, the language around shared responsibility is sometimes watered down. Moreover, because communities in the US have been designed around highways, Americans simply drive more than Europeans – which puts them at an elevated risk of being involved in a collision.

In February 2020, Sweden hosted a High-Level Conference on Global Road Safety for the United Nations. A group of Swedish experts, chaired by Tingvall, put together a set of recommendations and targets that would go on to enshrine Vision Zero in road safety policy for the UN, WHO and OECD.

The so-called Stockholm Declaration was agreed by around 140 members and was seen as an equivalent – for road safety – of the 2015 Paris Agreement on climate change. It kickstarted the UN and WHO's Second Decade for Action for Road Safety, which aims to cut road deaths and injuries by half globally by 2030.

That would be impressive – but what about zero? Will Sweden ever have a year when no-one is killed or seriously injured as Tingvall envisioned?

"Not in my lifetime," says Tingvall. "But I'm pretty old. Around 2050, maybe." But he adds that Vision Zero has been more successful than he anticipated. By some metrics, in some places, we are glimpsing zero: in 2019, Helsinki and Oslo reported zero pedestrian fatalities; in the Norwegian capital only one driver died that year. The general approach is to reduce deaths from cars by restricting their use; Oslo removed more than 1,000 parking spaces to discourage driving; Helsinki narrowed roads and widened pavements.

But for Tingvall, there are still areas of unfulfilled potential. He believes his own profession of road administrators should be held to account with a legally binding code of conduct, like that of doctors.

And while officials publicly back the idea of shared responsibility, police and prosecutors investigate crashes as they always have, with the emphasis still on the actions of individual road users. In a recent essay, Tingvall pondered if we need to clarify that road safety as a human right, to ensure people take it seriously.

Meanwhile, some of the core policies of Vision Zero have come under renewed political attack, especially in the UK. In July 2023, Prime Minister Rishi Sunak ordered a national review of low-traffic neighbourhoods – a design approach for cities that aims to eliminate through-traffic, to make streets safer for pedestrians and cyclists. It concluded that while low-traffic neighbourhoods in cities such as London have brought about some measurable improvements in road safety such as declines in road traffic injuries, more research was necessary to see if those changes were long term. In October 2023, the UK Government also unveiled its "plan for drivers" and pledged to restrict the use of 20mph speed restrictions in England.

"It's an extreme standpoint, and it goes against the Stockholm Declaration," Tingvall says. "It's extreme because the knowledge today is that there is no negative impact of speed restrictions on motorcars – you can even squeeze out more accessibility.

Perhaps counterintuitively, research shows that slowing vehicles down typically makes little difference to journey times in cities – it may even make it quicker to get from A to B. That is because  the traffic flow will be more harmonious, with fewer cars changing lanes and fewer collisions.

A spokesperson for the UK's department for transport told the BBC that while 20mph (32km/h) limits can be an important safety measure in residential neighbourhoods and around schools, local authorities should ensure they are supported by local communities and not used as blanket measures in inappropriate areas.

But Tingvall expresses regret that speed limits are still subject to political and public debate, rather than being set by experts who understand the risk that different road systems pose to the human body. "No one would dream of letting the Parliament set the speed limits for trains, or maximum load weights for bridges, since they are technical limits," he wrote in 2022. "Regardless of how hard it may sound, democracy does not stand above physical laws."

At the same time, speed-limiting technology is approaching a point of great life-saving power. All new cars sold in the EU now come with Intelligent Speed Assistance (ISA) as standard. Vehicles identify the speed limit on a stretch of road and either cut engine power if the car is speeding or give an audible warning. Drivers can override the function, or deactivate it altogether, but their actions will be recorded on a "black box" type device.

In time, cities will have the opportunity to "geofence" sensitive areas like schools to slow all motorised traffic down – something that effectively happens already with London buses, which are fitted with speed-limiting technology. Such a move would provide the ultimate example of transport authorities taking back responsibility for road safety.

Tingvall believes that Vision Zero has one more trick up its sleeve – and it could change the nature of the debate altogether. Building on his experience with Euro NCAP, he is currently working with the Fédération Internationale de l'Automobile (FIA) – the group which oversees motorsport and represents motoring organisations around the world – to create a safety rating system for organisations.

So far, they have calculated the "safety footprint" of just one company: the petrochemical giant TotalEnergies, but Ikea will be following soon and, Tingvall hopes, many other organisations.

Tingvall believes this could supercharge the way Vision Zero is implemented, leading to road safety improvements in supply chains that cross into the developing world, and removing the debate from the political sphere. Safety, Tingvall believes, is just like climate change – you can deny the science, but at the risk of your credibility.

"Of course, you need courage – a lot of courage," says Tingvall. "The courage for someone in public authority to say, 'This is where I draw the line between listening to politics, listening to science – and also human rights.'"