The cost of congestion on Canberra roads is set to double to $400 million by 2030 unless major infrastructure projects are completed, a government agency has warned.
Department of Infrastructure and Regional Development modelling has found the total kilometres travelled on ACT roads could increase from 3.9 billion to 5.2 billion by 2030.
The cost of congestion in Canberra has increased from $54 million in 1990 to $200 million in 2015, largely due to an increasing population in Gungahlin and Belconnen.
Nationally, the total cost of congestion is tipped to reach $30 billion in 2030. The costs have increased from $12.8 billion in 2010 to $16.5 billion this year.
Congestion in Sydney was the most expensive this year at $6.1 billion, followed by Melbourne at $4.6 billion, Brisbane at $2.3 billion, Perth at $2 billion and Adelaide at $1.1 billion.
Infrastructure Partnerships Australia chief executive Brendan Lyonssaid the report was a warning for Canberra policy makers to introduce bold reforms.
"Canberra has its own distinct challenges such as Northbourne Avenue, which is a nationally significant corridor with continuing congestion problems," he said.
"On top of that, you've got a spread out population with large developments in the north and south of the territory that put pressure on arterial roads."
The Department of Infrastructure findings were based on population projections, assumed capacity of existing public transport networks, increased operating costs, poorer air quality and extra travel time.
"Technology options, such as the rapid deployment of semi or fully autonomous vehicles, have the potential to significantly reduce projected congestion costs," the report said.
Earlier this year, an Infrastructure Australia audit warned congestion costs could reach $700 million by 2031 with Northbourne Avenue set to remain the most expensive road in Canberra.
The audit, which used a different form of modelling, found delays would increase significantly as the population of north Canberra continues to grow.
Minister for Capital Metro Simon Corbell said the report justified a decision to invest nearly $800 million in light rail.
"The evidence is absolutely clear and that is we can't afford to continue down the same path we always have and expect this growing problem to go away," he said.
"At upwards of $400 million a year the cost of doing nothing is far too high."
But shadow transport spokesman Alistair Coe said the installation of light rail would do little to ease congestion on Canberra roads.
"The government will continue to suggest that light rail will ease congestion but there is mounting evidence that it won't," he said.
"[We] believe making bus services faster and more reliable, in addition to road improvements such as the Barton Highway Flyover, are among the best ways to ease congestion across Canberra."
A trend report published by the department earlier this week found public transport demand would increase by 30 per cent by 2030, predominantly due to population growth.
The report also found Canberra had the lowest percentage of public transport costs recovered through user payments.
"Fare recovery in Australian urban mass transit systems is around 25–30 per cent, well below the level recovered in a number of transport systems internationally," the report said.
"This raises questions about accessibility versus cost recovery, the sustainability of current financial structures and the scope for further public investment in mass transport infrastructure and services."
Mr Lyons said the modelling should encourage politicians to embrace new ideas to address congestion and infrastructure.
"Charging drivers dependent on when, where and how they use their vehicles can change demand patterns," he said.
"If implemented effectively, it can cause reduced congestion in peak periods allowing city to function effectively, in turn reducing the avoidable costs of congestion."