Infrastructure Australia's 2019 infrastructure audit lays out the worst-case scenario for Australian cities, if the populations grow at their current rate and investment stops.

It tips the cost of congestion on Canberra and Queanbeyan roads to rise from about $289 million in 2016 to $504 million in 2031.

And while the William Slim Drive/Coulter Drive corridor is the most clogged road in the capital region today, increasing development in the Googong and Tralee areas will mean the Canberra Airport to Civic corridor will become Canberra's most congested over the next 12 years.

Delays would nearly double from eight to 15 minutes in the morning peak and from seven to 13 minutes in the evening peak from the centre of Canberra to the airport.

Commuters along the Canberra Avenue corridor would also experience extra delays, rising from eight minutes in the 2016 morning peak to 12 minutes in 2031, and from seven to 11 minutes in the evening.

If this scenario materialises, drivers on the region's worst affected routes would also spend half their trip bumper-to-bumper.

Motorists heading west on the Canberra Airport to Civic corridor in the morning would spend 54 per cent of their trip in congestion, up from 39 per cent.

Those driving west on Canberra Avenue in the morning peak would spend 51 per cent of their trip in heavy traffic, compared to 39 per cent in 2016.

The daily cost of the clogged roads would rise from $800,000 to $1.5 million per day.

And even projects like the long-awaited Gundaroo Drive duplication won't ease the pressure for long, Infrastructure Australia found.

One of the worst-performing roads in 2016, Gundaroo Drive, is expected to become even more congested by 2031 by virtue of population growth.

Drivers are also expected to ditch their current routes and use the road when it is finished in 2021, the report said.

READ MORE:

However, it's not all bad news.

The William Slim/Coulter Drive corridor is expected to drop off the list of top 10 congested roads altogether, due to a duplication of a parallel section of Gungahlin Drive.

Investment in light rail and extra bus services is also expected to see a modest increase in the percentage of people taking public transport to work, from 3 to 4 per cent.

But while demand for public transport has grown in Canberra over the past 10 years, it has still increased at a slower rate than for cars.

In 2016, 75 percent of commuters drove to work while 22 per cent walked or rode bicycles.

Nationwide, the cost of congestion is tipped to blow out to around $40 billion if population growth continues at current rates without serious investment.

The Artarmon to Sydney Harbour Tunnel corridor was deemed the worst road in Australia, with commuters spending 81 per cent of their journey in congestion and experiencing a 16-minute delay on average.

The stretch is expected to become even worse in 2031, rising to a 19-minute delay and 84 per cent of journey time spent bumper-to-bumper.