COVID-19 may have kick-started the decline of the Australian CBD, but our newly published research shows how planning decisions had already created cities that lacked resilience.

The changes in our work preferences have highlighted how vulnerable our cities are to economic shocks. Moves to entice (or compel) workers back to the office may be just a short-term fix for precincts now struggling with low levels of foot traffic.

Historic zoning practices created separate areas of residential, commercial and industrial activity in our cities. This practice created whole precincts like the CBD and residential suburbs dedicated to a single use.

The lack of diversity arising from this pattern of development ultimately reduces resilience when conditions change. It is arguably one of urban planning’s greatest failures.

The most resilient places during COVID-19 lockdowns were those that had a diverse industrial employment mix. It meant they did not rely on a single sector for jobs – and the lockdown impacts varied from sector to sector.

For example, Melbourne’s last remaining inner-city industrial zone, Port Melbourne, provides a diverse mix of production as well as commercial services. It was among the most resilient places of employment in Australia to COVID impacts. This example offers valuable insight into a truly “mixed use” precinct.

Areas with diverse land uses became the goal of new planning policies that emerged in the 1980s. By introducing zoning changes, policymakers hoped to replicate the vibrant, dense and localised environments of older cities that predated the rise of cars.

However, our research shows policies that aimed to increase land-use mix do the opposite in practice.

Our research found a large increase in commercially zoned land across all study areas. Rezoning former industrial precincts accounted for most of this increase. While residential use remained the dominant land use across all study areas, commercial use grew from 2.3% of combined land area in 1951 to 28.9% in 2021.

As a result, by 2021, commercial services provided almost all the jobs in these areas. Most of the land zoned as mixed use, which allows low-impact industry (such as vehicle repairers, shop fitters and printers), was used for housing, shops, gyms or offices.

By allowing open competition between commercial, residential and industrial uses, policy aiming to diversify land uses has the opposite effect of sidelining industrial use. One reason is that centrally located industrial sites are often large and under single ownership, which makes them a prime target for developers.