Sydney (AFP) - Australia must pour more money into transport systems or risk gridlock in its biggest cities costing more than Aus$53 billion (US$42 billion) a year, an infrastructure audit published Friday found.
Road congestion across Australia's six largest cities, particularly in Sydney, cost the vast country some Aus$13.7 billion in 2011, the Infrastructure Australia report said.
But the economic toll could rise to Aus$53.3 billion a year in 2031 unless more money is invested, it added.
"The costs of delay -- to ourselves, to our businesses and to our economy are almost never counted," Prime Minister Tony Abbott said as he launched the report and pledged his government's commitment to funding infrastructure projects.
"Aus$53 billion a year in congestion costs in just 15 years' time -- that's more than Aus$1 billion every week."
Sydney, Australia's largest city, is already home to seven of the 10 worst road corridors in the island continent, the report by the independent government body said.
Along with five other cities -- Adelaide, Brisbane, Canberra, Melbourne and Perth -- Sydney could see car travel times on the most congested roads double by 2031.
At the same time, the nation's four largest cities were projected to have population growth of about 45 percent to 18.6 million in 2031. Australia's overall population is projected to grow from 23.3 million in 2011 to 30.5 million in 2031.
The report said while infrastructure gaps were most visible in urban transport, the quality and reliability of water services in some rural towns were also of concern.
It added that Australia's infrastructure investment compared poorly with countries that have similar population densities and harsh weather conditions, such as Canada.
But question marks remain over how new infrastructure spending could be funded, the report said. It added that a national discussion was needed as the future demands of supporting wealth and health services could eat into public spending on infrastructure.
Abbott, who said previously he wanted to be known as an "infrastructure prime minister", has committed to investing billions of dollars in upgrading road and rail links.
The government is also giving states and territories financial incentives if they sell their assets and reinvest them in infrastructure projects.