Disability-adjusted life-years (DALYs) gained per 100,000 population under the compact cities model (source: Stevenson et al)
The Australian Medical Association's (AMA) Position statement on obesity 2016 released yesterday includes a strongly worded call for urban policy makers to prioritise physical activity:
Creating healthy communities should be the goal of town planning. Planning regulations governing housing, urban development, and transport infrastructure should mandate the incorporation of measures to promote and facilitate physical activity.
Whether health should have the same priority in urban policy today that it had in the middle of the nineteenth century is doubtful (see London in the time of cholera), but some health researchers certainly regard the physical form of cities as a key to improving contemporary health concerns.
The Age reported recently that a new study published in The Lancet suggests "our beloved city could be making us sick". How so? "Cars. And lots of them". Stevenson et al examine the health benefits of a more compact urban form in their paper, Land use, transport, and population health: estimating the health benefits of compact cities. They explore the link between urban form and health in six cities: Melbourne, Boston, London, Delhi, Sao Paulo and Copenhagen
The paper's notable for having as many authors as a cricket team (including the twelfth man). It's significance though is in the finding that a markedly more compact urban form in a city like Melbourne would reduce cardiovascular disease by 19% and type 2 diabetes by 14%.
From the abstract:
Land-use changes were modelled to reflect a compact city in which land-use density and diversity were increased and distances to public transport were reduced to produce low motorised mobility, namely a modal shift from private motor vehicles to walking, cycling, and public transport. The modelled compact city scenario resulted in health gains for all cities (for diabetes, cardiovascular disease, and respiratory disease) with overall health gains of 420–826 disability-adjusted life-years (DALYs) per 100 000 population. However, for moderate to highly motorised cities, such as Melbourne, London, and Boston, the compact city scenario predicted a small increase in road trauma for cyclists and pedestrians (health loss of between 34 and 41 DALYs per 100 000 population).
The net health benefit for Melbourne is estimated at 679 additional disability-adjusted life-years (DALYs) per 100,000 population. It's almost entirely due to reduced cardiovascular disease from increased exercise associated with the assumed shift to active travel modes i.e. walking, public transport and cycling.
Getting those benefits though wouldn't be easy in our current political system. Bringing about the scale of change in urban form assumed by the authors would be a herculean task:
Under the compact cities model we increased land-use density by 30%, reduced average distance to public transport options by 30%, and increased diversity of land use by 30%. We combined these changes with an additional transport policy initiative that supported a 10% modal shift away from private motor vehicle driver and passenger VKTs (excluding motorcycles) to either cycling (two thirds of the total shift) or walking (a third of the total shift).
Just the last one – a 10 percentage point shift in mode share away from cars to cycling and walking – assumes an urban form and set of policies that're vastly different from Melbourne at present. It would take a long time and require the sort of interventionist policies – like road pricing and getting very serious about removing barriers to redevelopment – that politicians have clearly shown they've no appetite for (e.g. see Can the politics be taken out of infrastructure planning?).
Still, if the benefits are there it makes sense to push for change. The really interesting thing though is the net benefits estimated by Stevenson et al aren't all that big. When they're all summed, the net gain from applying the compact city model to Melbourne would be 679 extra disability-adjusted life-years (DALYs) per 100,000 population. Sounds impressive but that would be an average of 2.5 days of additional (healthy) life per person. Better than a poke in the eye of course, but it's not a big increase compared to the average life expectancy of males in Australia (around 29,200 days), or for women living in the City of Melbourne (31,719 days). Some would be bound to think it's a tiny pay-off for having to walk more for most of their life instead of driving, or having to live in an apartment rather than in a detached house.
There are however other good land use and transport-related reasons to promote higher densities in established suburbs and to encourage a shift from driving to walking and cycling (and public transport too). The modest health benefits associated with a more compact urban form suggest that urban policy-makers should focus the great bulk of their effort on those traditional concerns. It also prompts the question whether improving public health outcomes might be better pursued in other ways than via strategic planning and transport policies.
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