The cost of road congestion in south-east Queensland is set to triple to $6 billion in lost productivity in the next 12 years, with motorists travelling to and from Brisbane's south-west suburbs tipped to be the worst-affected.

An Infrastructure Australia audit has found an unexpected lift in Australia's population, concentrated in the major cities of Sydney, Melbourne, Brisbane and Perth, was straining everything from crowding on buses to the supply of schools on the urban fringe.

Infrastructure Australia chief executive Romilly Madew said Australia's infrastructure needs were rapidly increasing, with the economy becoming more urbanised.

Romilly Madew says the infrastructure boom "is the new norm" and needs to increase. Credit:Eamon Gallagher

"This infrastructure boom that we are in is the new normal," she said. "If we don't continue this investment, the costs of congestion will double."