Melbourne and Sydney have experienced significant growth and both are predicted to reach the current population of New York by around 2050. Efforts to decentralise population growth to regional centres have had limited effect.

Australia's major cities are playing catch-up with roads. Credit:Eddie Jim

Population growth puts pressure on health, education and other services. But a key policy issue in both cities is “congestion” – the challenges in just moving around.

Both cities are among the largest in the world by area, with low density making them costly to serve and making any material underground rail network prohibitively expensive.

Sydney awoke to the issue in 2011, developing WestConnex, NorthConnex, a large package of western Sydney works, Sydney Metro and light rail projects.