Sydney’s urban sprawl grew along rail lines similar to way cancer spreads, researchers say | Urban planning

Posted by

Sydney is renowned for its sprawl. Its geographical size is on par with Mexico City (population 20 million), Paris (10.4 million) and Bangkok (14.6 million), but Sydney’s population of 5.3 million pales in comparison.

Now researchers have developed a model of how it spread out, likening the city’s sprawl to how cancer spreads through a human body.

Researchers used mathematical modelling to reconstruct urban growth in Sydney from 1851-2011. Along with finding that Sydney’s population size and spread has evolved in a manner similar to a tumour, they also concluded the rail system has “coevolved” with the urban population: that is, transport investment is not only demand driven – it also causes urban change.

Sydney’s development began with an initial phase of “limited growth around the city centre”. The expansion of the train network – which took off in Sydney in the 1890s – led people to move to the suburbs, expanding both the population’s size and spread.

“The more train lines you have, the more territory that can be covered,” David Levinson, a co-author of the study and a professor of civil engineering at the University of Sydney, said.

“That territory has developed more and more intensely … similar to the process by which malignant tumours form.”

An aerial view of western Sydney. The expansion of the train network in the 20th century led people to move to the suburbs, expanding both the population’s size and spread. Photograph: Brook Mitchell/Getty Images

However, Andrew Butt, a professor in sustainability and urban planning at RMIT who was not involved in the study, said solely attributing urban growth to transport links failed to take personal preferences about where people want to live into account.

“While it’s a great analogy, the city is not simply an accretion. It’s actually a formation of lots of little places that exist,” he said.

He said the modelling didn’t “adequately account for the very local experience of place that people have”.

The researchers did note a few disparities between their model of cancer-like growth they developed and what has actually happened in Sydney’s urban sprawl. For instance, highly sought-after coastal locations, such as the Northern Beaches, are not near any rail network.

These discrepancies “show us the city doesn’t do the things we expect it to do…because people genuinely have preferences and want to make choices”, Butt said.

skip past newsletter promotion

Lessons from growth

Levinson said the study illustrated an important point – that Sydney’s infrastructure could be better used.

“Sydney has a disproportionate number of jobs in the eastern side of the city, and a disproportionate number of residents in the western part of the city,” he said.

This leaves transport underutilised compared to other cities around the world, where housing and jobs are more evenly spread out.

Butt said it was “inherently unsustainable to have everything focused in so few places”.

“Having local work and local possibilities should be the ultimate aim of cit[ies].”