Despite massive investment in public transport over the past few decades, cars remain the premier choice of transport for most Perth residents, particularly those on the fringes of the city where access to jobs, schools and hospitals still depend on driving.

Key points: The Mitchell and Kwinana freeways remain the most congested roads in Perth

The Mitchell and Kwinana freeways remain the most congested roads in Perth It's quicker to go by car to hospitals, schools and childcare centres than use public transport

It's quicker to go by car to hospitals, schools and childcare centres than use public transport The daily cost of road congestion will surge from $4.4 million to $10.5 million by 2031

These are some of the findings of an Infrastructure Australia audit of the nation's transport needs over the next 12 years that found the cost of road congestion in Perth is set to more than double, from $1.5 billion to $3.6 billion.

It also found the Kwinana Freeway among the 10 worst roads in the country for delays. It was currently ranked at number nine, but was set to worsen over the next 12 years to become the seventh worst in Australia.

Yet things could be worse.

Getting into the city for work is about to get even harder. ( ABC News )

When the last report was released in 2016, the advisory body was forecasting congestion costs would rise to almost $16 billion in the same period, based on population and employment projections calculated at the height of the mining boom.

But more recent figures suggested Perth's population growth would be 22 per cent less that originally thought, growing to about 2.6 million by 2031.

Areas such as Rockingham (with 107,000 fewer residents) and Wanneroo (101,500 fewer) showed the biggest disparities from the 2016 forecasts.

But these urban fringe areas were expected to grow the fastest in the next 12 years, with Wanneroo's population set to surge 75 per cent and Mandurah up 58 per cent.

Hospitals, schools reveal transport woes

Perth's transport problems were encapsulated by the problems accessing hospitals.

Every major public hospital in Perth is close to a railway station except Sir Charles Gairdner, yet the audit found it was still far quicker to travel by car to any of them.

By public transport, the average travel time would be more than 50 minutes by 2031, yet by car it would be 16 minutes (up from 12 minutes currently).

Average times to the nearest Perth hospital by car (left) and public transport (right) in 2031 during the morning rush hours. ( Supplied: Veitch Lister Consulting )

The same was true of accessing schools and childcare.

While most people could get to their local schools and childcare centres in under five minutes by car at present (rising to seven minutes by 2031), the same journey by public transport already took more than 30 minutes and was set to increase further by 2031.

But rising road congestion is forecast to affect your ability to drive to work in 2031.

Fewer jobs would be accessible by car, particularly for people living south of the river. But those in the outer suburban fringe, where public transport options were more limited, would still be hard pressed to get to work in a timely manner.

"Perth residents without use of a car have significantly reduced access to social infrastructure today and in the future," the report found.

"In central Perth public transport offers a realistic alternative to car ownership and use. However, on the urban fringe and in other outer areas this is not the case."

Freeway congestion to increase

More money had been invested in roads and public transport since 2016, most notably the Metronet project.

The WA Government's Metronet train line expansion plan. ( Supplied: WA Government )

But our continued reliance on the car meant heavy road congestion was set to increase on roads throughout the metropolitan area, especially those leading into the city.

"… High congestion is still forecast to occur on local and arterial roads in the Perth CBD. West Leederville, Subiaco, Leederville, North Perth and [Mt] Lawley are also predicted to maintain high congestion forecasts on their local roads," the audit found.

"Perth's most congested corridors are major north-south freeways and the arterial roads feeding those freeways, as well as key river crossings which act as pinch points in the network."

Alternative routes into the city were also heavily congested at peak times, including Marmion Avenue/West Coast Highway in the north and Old Coast Road/Mandurah Road/Stock Road/Stirling Highway in the south.

The report found freeway commuters already spent about 40 per cent of their time stuck in traffic. By 2031 this was forecast to jump to up to 60 per cent, and those on alternative routes would also feel the pain.

The daily cost of road congestion would surge accordingly, from $4.4 million a day in 2016 to $10.5 million by 2031.

The Kwinana Freeway will remain one of the top 10 worst congested roads in Australia. ( Grant Wynne )

This was despite planned investment in a range of major transport projects including freeway widenings, the Forrestfield Airport Link, Northlink and the Thornlie-Cockburn Link.

"In 2031, Perth's worst-performing roads will be broadly the same as today, but suffering greater congestion and delays," the report found.

"The north-south Mitchell and Kwinana Freeways, and their connecting routes, are expected to experience the city's worst traffic congestion in 2031.

"Motorists can expect lengthier periods of congestion stretching greater distances from the city centre in both the morning and evening by 2031.

"Modelling suggests that by 2031 the Mitchell Freeway will be struggling to accommodate an expected traffic volume well in excess of its design capacity."

Buses, trains to get more crowded

The use of public transport has declined in Perth in recent years, though it was still higher than it was 10 years ago and there was standing room only on the busiest rail lines — the Joondalup and Mandurah lines — during peak hours.

Crowding on Perth trains, especially on the Joondalup and Mandurah lines, is set to increase. ( ABC )

But the increasing population meant demand for public transport would grow 42 per cent by 2031, compared with a 32 per cent increase in car trips, and train and bus services would struggle to keep up.

Crowding would be particularly acute on the Mandurah Line between Parmelia and Jandakot, and on the Joondalup Line from Woodvale into the city, especially in the morning peak when demand would exceed capacity.

Buses were forecast to get more crowded too as people avoided jam-packed trains, with Kwinana and Mitchell Freeway services among the worst affected.

As a result, the annual cost of public transport crowding would rise almost 10-fold, from $17 million to $159 million.

Demand for buses and trains is set to surge in the next 12 years. ( ABC News: Glyn Jones )

Transport Minister Rita Saffioti said the Government should be commended for improvements in the state's transport networks since taking office.

While acknowledging reduced population growth forecasts played a part, she said the Government had invested heavily in roads and public transport and was continuing to invest in problem areas including the freeways, Tonkin Highway and Marmion Avenue.

She said some planned infrastructure — including the Ellenbrook rail line — had not been included in the report, so future congestion would not be as bad as forecast.

There were also plans for public transport upgrades, including an order for 246 new, bigger rail cars, and more housing density around train stations.