Reclaiming cities from cars
How Dr Audrey de Nazelle is helping to build healthy, green cities of the future
When Dr Audrey de Nazelle was 19 years old, she was stopped by a French police officer who gave her a ticket for running a red light on her bicycle. She was outraged. She had spotted the police car on the opposite side of the street, having ridden through an empty pedestrian crossing just before the light turned to red.
Still a mathematics and physics student in university, Dr de Nazelle went to court to argue her case. “I didn’t want to pay the fine, it was really expensive – almost as expensive as the bike – which was a moral outrage. I felt it was wrong to discourage rather than encourage cycling,” she says. “I had three months to really think through my argument, and I developed this really good argument about why we needed to promote cycling rather than discourage it.”
Did it work? Dr de Nazelle shrugs and explains that the judge cut her fine in half, and she was never pursued to pay the remaining half. But that event affected her. After her court case, she began organising bicycle demonstrations where she and her fellow cyclists took over the roads of Paris.
I felt it was wrong to discourage rather than encourage cycling.
She became involved with the Young Greens whilst still pursuing her studies. The protests she took part in eventually led to the creation of a bicycle committee that promoted cycling in the Mayor of Paris’s office, to which she was then invited.
“Eventually, I thought, I don’t want to become a professional politician and abandon my studies. I should be studying where my heart is,” Dr de Nazelle says. The young activist left for the US to do a PhD in environmental studies at the University of North Carolina at Chapel Hill, where she was able to specialise in public health and urban planning.
These early experiences contributed to a passion for creating environments with cyclists and pedestrians in mind which she explored at the University of North Carolina. This culminated in her thesis, which studied the transformation of cities towards being more walkable and bike-able, and the positive health impacts of a city without cars.
Dr de Nazelle is now a Senior Lecturer at the Centre of Environmental Policy (CEP) at Imperial, and also is the co-chair of the International Society for Environmental Epidemiology – a field that studies the effects of physical, biological and chemical environmental factors on human health.
Since joining Imperial in 2012, Dr de Nazelle has helped to build a substantial evidence base that supports cities transitioning away from car-orientated infrastructure.
A deceptively small change, she points out, can result in a cascade of potential benefits to public health: amongst them, reduced air pollution, increased physical activity, and the transformation of reclaimed urban space for parks and green spaces.
“By putting all these systems together, we're not making decisions in siloed ways but rather thinking of how everything connects,” she says, “And you realise you’re actually getting a really big bang for your buck when pushing forward certain policies because they have holistic impacts.”
Dr de Nazelle’s field can be tricky to study due to the overlap of different variables that are difficult to quantitatively analyse and model. On the surface, these variables could seem completely disconnected, or, quite the opposite, may seem completely inseparable. For that reason, Dr de Nazelle struggles to summarise the research interest that has occupied her academic career.
“My research is super broad, it's multidisciplinary and transdisciplinary,” she says, “But I’d say that my primary focus is cities and health: how do we make cities healthier?”
Health and the city
In the 1850s, the idea of ‘urban planning’ was born. Due to the Industrial Revolution, there was a mass migration to rapidly growing cities such as London and Paris, often coupled with devastating health consequences that fell disproportionately on the poor.
Sprawling slums where migrants often settled were constantly threatened by crime and disease outbreaks, such as cholera outbreaks seen in England that were driven by the deteriorating quality of urban water supplies. The severity of urban crises prompted the development of modern city planning.
Western governments had already begun collecting population-wide data via censuses. The data provided people with a snapshot of their growing cities through figures like infant mortality and household sizes.
The collection of these large quantities of data allowed scientists and physicians to begin to understand the relationship between poor health outcomes and environmental factors across districts of the city (such as where that district sourced its water, soil type, exposure to the sun, elevation).
Major cities began to integrate public considerations into their design – New York, Barcelona and Paris being but a few key examples. Urban planners became more cognisant of how the built environment could not only change what people were exposed to, but also individual behaviours.
In 1886, the first car was invented. Since then, automobiles have dominated many aspects of urban design. There are over 64 million kilometres of road networks in the world – the equivalent of roughly a million Nile rivers. The UK’s road network is over 400,000 kilometres long. Road networks are not the only thing needed to support a society reliant on cars, though; petrol stations and carparks also take up significant space.
But the car allowed people to travel further faster, leading to the growth of suburbs where basic amenities, such as grocery stores and communal spaces, could be located miles away.
“I think we just had years of completely forgetting the connection between health and cities,” Dr de Nazelle says. Historical research at institutions such as the CEP demonstrated how pollutants emitted by cars lead to a variety of environmental and public health hazards – asthma, cancer, and even dementia to name a few.
Building the evidence base
“I think when you cycle, you realise very intuitively that your life is just better, both when you’re in transport and outside it,” says Dr Juan Pablo Orjuela, Senior Research Associate in urban mobility in the University of Oxford, who was Dr de Nazelle’s PhD student during his time at Imperial.
“I think the important thing is to put numbers to that. We have actual evidence to show that this is the case in the populations that we work with,” he says.
The tools that Dr de Nazelle helped to develop have enabled researchers and policymakers to quantify the health effects of building infrastructure for cyclists and pedestrians.
One of Dr de Nazelle’s first major contributions was to demonstrate the trade-off between the health risks posed by walking and cycling in polluted air versus the health benefits of increased physical activity: “Back then, nobody looked at models of health impacts that integrated physical activity, air pollution and traffic injuries.”
Such a modelling study required Dr de Nazelle to become familiar with methods of analysis usually employed by epidemiologists. This meant looking at pre-existing literature – some used cohort studies, some used controlled experiments – to inform the design of her mathematical model.
“What we found systematically was that the benefits outweigh the risks in most cases,” she says.
A newspaper clipping of Dr Audrey de Nazelle, published in the International Herald Tribune on 14 July 1995. It shows her holding up her bicycle as she protested increasing motor traffic in Paris.
A newspaper clipping of Dr Audrey de Nazelle, published in the International Herald Tribune on 14 July 1995. It shows her holding up her bicycle as she protested increasing motor traffic in Paris.
Over the years, her work has expanded to encapsulate more and more interconnected impacts: air pollution, noise, heat, the conversion of road infrastructure into green spaces and more.
Dr de Nazelle says: “It makes no sense to look at these things individually, but to look at it jointly, we need to bring together people from different fields and create alliances across different departments.”
Synthesising methodologies from vastly different areas of research can be a daunting task, says Dr de Nazelle: “It can be a difficult field to be in. Multidisciplinary work is not always rewarding though everyone says we need it – and it’s hard to be seen as an expert in anything when you work across fields.”
Politicians and people see the big picture, so researchers have to too.
However, Dr de Nazelle feels that multidisciplinary work is the only approach that makes sense for driving forward change. “Politicians and people see the big picture, so researchers have to too,” she says.
Quantifying impacts
Dr de Nazelle works on quantifying environmental and health impacts of transitions towards less car-dominated cities. You will see a few of the different benefits she considers to help support urban policies.
CO2: Reducing motorised travel is the most effective way of cutting land transport emissions.
Physical activity: Replacing car trips with walking and cycling will help the population reach recommended levels of physical activity. Changes in urban design, transport infrastructure and land use are needed to promote active travel. Physical activity is important for preventing and managing diseases like heart disease, diabetes, cancers and for improving mental health.
Noise: Reducing traffic can also reduce urban noise. Long-term exposure to noise has negative health impacts, such as sleep disturbances and hypertension.
Road accidents: Transitioning away from cars can also reduce the frequency and severity of traffic injuries, preventing potentially thousands of preventable deaths in the UK. Safe infrastructure for pedestrians and cyclists is needed for healthy transitions.
Air pollution: Cars are major contributors to harmful air pollution emissions in cities, such as fine particles (PM2.5) and nitrogen dioxide (NO2). Everyone benefits from reductions in air pollution, particularly the young, the elderly and more deprived populations.
Green spaces: Repurposing car infrastructure for green spaces, such as parks or trees, not only has environmental benefits, but has also been shown to have mental health benefits. Creating urban green spaces could help tackle anxiety and depression.
Dr Orjuela says that the tools that Dr de Nazelle has helped to create are open-source: “I think the important contributions in this research come from the ability to combine all these different benefits and costs, and that has been translated into an interface that anyone can use for free.”
“For example, if you’re a policymaker in Milan, and you want to create 10 kilometres of cycle lanes, and you don’t know the health benefit of that, you can now go online and calculate that in a matter of minutes,” he says.
It is not the first time Dr de Nazelle has needed to consider the persuasive impact her work would have on the political process. Organising bike demonstrations as a young student primed her to reach out to politicians as a natural extension of her work to better understand the evidence base that would motivate change.
Whilst doing her PhD, she was involved in committees in her local mayor’s office. “Back then, it wasn’t called co-creation and I certainly didn’t know it existed, but I felt it was necessary to look at what politicians wanted before going out to do the research,” she says.
Now, her work has evolved to tackle understanding this political process more systematically: looking at what triggers policy change after years of inertia.
Dr de Nazelle’s research does not limit itself to engaging policymakers either. She says she’s currently developing a mobile app for people to engage with her research by interacting with different triggers that may motivate them to walk or cycle more often.
“I’ve done research now about how promoting walking and cycling can reduce social isolation, reduce stress, reduce obesity,” she says, “I think I want to find what hooks actually work to get people to change how they behave.” That way, Dr de Nazelle says, normal people who want infrastructure for cyclists and pedestrians can be the catalysts for change.
Decades after being issued a ticket by a police officer, Dr de Nazelle still remembers her time campaigning as a Young Green member.
“The Young Greens – my friends and colleagues –they were so incredibly visionary. To everyone else in the world, we looked like some young kids making up wild dreams, but no, we weren’t. We were completely serious.”
Reclaiming cities from cars
Written by Jacklin Kwan, 2023
This story was published as part of a collection for World Environment Day, profiling the work of researchers at the Centre for Environmental Policy. It highlights the real-world policy work of Imperial's environmental researchers to influence policy and legislation.
Image credits:
- Paris Streets: Odair Faléco via Wikimedia Commons
- Ca. 1870 map of Paris by Eugene Deschamps: Public domain vis Wikimedia Commons
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