International team of scientists urge action at all levels of society
Last year, I interviewed Distinguished Professor Billie Giles-Corti, Director of the Healthy Liveable Cities Lab, for a piece on walkability. During our conversation, she mentioned a large, international study she was undertaking. Focused specifically on the links between urban design, transport, and health, the research has just been published as a Series in leading medical journal, The Lancet. So, I thought I’d dive into all four papers of the series, and give you an overview of its findings and recommendations.
The first thing to say is that Giles-Corti hasn’t done this alone. She is joined by an interdisciplinary team scattered across the globe, whose members have expertise in a wide range of topics – city planning, population health, environmental science, big data, public administration and transport, to name just six. Many of these experts also collaborated on an earlier series (published in The Lancet in 2016) which looked mainly at the reasons why urban societies need to make the transition to creating healthy and sustainable cities.
The 2016 series also proposed as set of “city planning policy and spatial indicators to benchmark and monitor progress towards achieving healthy and sustainable cities.” As I reported previously, these are summarized as ‘the eight D’s’, and they can be thought of as the pathways through which city planning directly affects health: 1. destination accessibility, 2. equitable distribution of employment, 3. demand management, 4. designing pedestrian-friendly and cycling-friendly networks, 5. diversity of land use, 6. optimum residential density, 7. reducing distance to public transport, and 8. enhancing the desirability of active travel modes.
In the new series, the team wanted to expand upon this earlier work. And so, across the four open-access papers, they ask (and answer) questions around what must change in order to create healthy and sustainable cities. Part of that, they say, involves transforming their indicators into a global, open-source policy system; one that helps planners and policymakers to make better, evidence-based decisions on how to develop the urban landscape to the benefit of its inhabitants. And what’s clear is that, as an ever-urbanizing society, we’re not doing nearly enough.
The first paper looks at the status of existing planning policies in 25 cities across 19 countries (a mix of low-, middle- and high-income regions). The goal was “to identify whether these policies supported the creation of healthy and sustainable cities.” Working with researchers local to the city, they collected and coded data on 24 key categories, including air pollution, the ratio of jobs to housing, parking restrictions, and requirements for provision of public space.
In short, what they found was a lot of talk, but very little meaningful action. Despite lots of rhetoric and public messaging on the importance of building more sustainable cities, very few of the study cities had specific and measurable policy targets. For example, 92% of the cities had requirements for pedestrian infrastructure, but only 32% (8 cities) had targets that actually could be measured. It’s virtually impossible to monitor progress – and to be held accountable – on interventions if you don’t have something to measure them against.
In some cases, even measurable targets were found to be inconsistent with existing public health evidence. They gave the example of Melbourne, which has a target “to increase density in growth areas to more than 20 dwellings per hectare” in order to support walkability. However, numerous other studies have found that at least 25 dwellings per hectare are required to enable this mode shift. Other cities required plentiful parking availability in new developments, despite discussing the importance of active and mass transit provision in healthy cities. The authors conclude that “There is an urgent need to strengthen policy frameworks for health-enhancing city planning, particularly in low-income and middle-income countries.”
Paper two looked at walking in cities. Specifically, it reports on the minimum thresholds for urban design and transport features that allow people to meet two very specific criteria for physical activity: 1. at least an 80% probability of engaging in walking for transport, and 2. at least 15% relative reduction in insufficient physical activity through (total) walking.
The authors chose these two criteria because they relate to other international targets. Walking for transport supports several of the UN’s Sustainable Development Goals (SDG), including making cities inclusive, safe, resilient, and sustainable (SDG 11), and mitigating climate change (SDG 13). In addition, the World Health Organization (WHO) has shown that doing at least 150 min per week of moderately-intensive physical activity – e.g. walking for transport or recreation – bestows significant health benefits.
Their sample – gathered via a global physical activity study called IPEN – included 11,615 participants from 14 cities, 11 of which were in high-income countries, with the remaining three in upper-middle-income countries. Unfortunately, this paper didn’t include any data from low-income countries.
One of their findings was that there is an inverted-U relationship between public transport density and the probability of walking for transport. Neighborhoods that offered at least 25 stops per km² were associated with meeting the first of the two criteria. A similar analysis that included population density and street intersection density identified another set of thresholds – neighborhoods with around 5700 people per km² and 100 intersections per km² tended to yield optimal outcomes for ‘total walking’ guidelines.
In the third paper, the team addressed the need to better measure, map, and compare those urban design and transport features known to be important in creating healthy, sustainable cities. They did this by developing a new tool – an open-source framework that allows planners to compare various indicators both within and between cities around the world.
Led by Professor Geoff Boeing, Director of USC’s Urban Data Lab (and someone whose work I’ve featured previously), the authors started by revisiting the eight indicators introduced in the 2016 series. Using a variety of open-source data, they then linked these indicators to the policies identified in the first paper of the 2022 series. And in order to examine within-city inequities, they also identified populations living above and below the critical thresholds identified in paper #2. Their key output was a series of maps that showed a huge variation in the provision of resources and amenities.
For example, the population percentage within a 500 m walk of a healthy food market varied from 6% (Phoenix) to 70% (Bern). There were also substantial inequities in access to public open space: only 42% of the population in cities of middle-income countries lived within 500 m of such a space, compared with 75% in cities of high-income countries. Older, compact cities offered the best walkability (regardless of economic status). The authors write that the “worst performing cities for walkability were in high-income countries including the USA, Australia, and New Zealand. These cities were developed primarily in the 20th century under a car-centric planning model.’”
Mass transit coverage varied too. More than 95% of São Paulo residents were estimated to have access to frequent public transport, compared with 62% of Bangkok residents. This is despite the fact that the two cities have similar populations and a large proportion of their residents living in informal settlements. Interestingly, the study showed that São Paulo’s policy framework outperformed that of many cities in high-income countries.
This paper was a proof of concept. It demonstrated the feasibility of producing a framework that can reliably benchmark cities on urban design and transport features important for public health and sustainability. But, the authors say, taking it further will require broader collaboration, engagement, and investment, “If the goal is the public good, then open source should be the default for government data and analytics……Open data and open-source tools together create an opportunity that, for the first time, enables built environment, health, and policy researchers to quantify and monitor the progress of their city and compare local results across cities globally.”
And finally, there’s paper four, which summarized the key findings of the earlier papers, and placed them in a broader context. It expanded the framework, adding three more ‘D’s’ to the original eight: 9. Destination proximity, 10. Disaster mitigation, and 11. Distributed interventions. It also considered what to do next, and outlined the urgent key actions needed, if we’re to stand any chance of making our cities better.
The main takeaway for me was that cities must urgently move from evidence to action. Countless studies have shown the co-benefits of a compact, walkable urban form that does not necessitate the use of private cars, and which invests in green spaces. We already know that fewer cars on the road makes walking and cycling safer, and reduces air pollution. We know that improvements in air quality will lead to a reduction in the prevalence of cardiovascular and respiratory disease, improving human health. We know that cities that prioritize affordable mass and active transit are more equitable, and experience less traffic congestion. We know that green infrastructure can reduce the urban heat island effect, mitigate the impact of flooding, sequester CO2, and provide open space for people to enjoy. We know all this stuff. What’s stopping us from actually building it?
The authors really emphasize the need for closer collaboration between disciplines. They write, “City planning issues are often considered in silos (e.g, focused either on transportation or urban planning or biodiversity)…. there is an urgent need to rethink this siloed approach in favour of interdisciplinary research and cross-sector, integrated policy and practice.” They also urge city leaders to make the decision-making process more accountable, transparent and participatory, and to create, use, and share open data.
We urgently need a more integrated approach to urban planning; one that takes all of the existing evidence and knowledge we’ve acquired, and transforms it into cities that work for us and for the environment. As Giles-Corti concludes in this paper, “Without comprehensive and integrated implementation of the [interventions], human health will be harmed by car-centric planning.”