It has been more than two decades since West Australians were happier with their public transport options than they are now.

More than nine out of 10 Perth people who catch public transport say they are satisfied with the service they get, according to the latest results from Transperth's passenger satisfaction survey.

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In addition, 95 per cent are happy with the punctuality of Transperth's offerings — while similar numbers say they are satisfied with service frequency, cleanliness on board and the availability of seats.

"I think it is a very good system," Transport Minister Rita Saffioti said.

"People that use the system really enjoy using it."

The numbers paint a rosy picture of the state of Perth's public transport options, but there is one significant problem that is costing taxpayers dearly.

People are just not using public transport as much as they used to.

The rate of decline shows no signs of slowing down either, with the number of people catching trains falling by nearly 10 per cent in five years and bus boardings dropping by around 5 per cent.

To put that into perspective, in just two years, the number of bus and train passengers fell by eight million.

Gambling on a turnaround

Theories vary as to why — fare hikes, congestion on bus routes and a lack of services in growing outer corridors are among the many suggested.

The drop-off has hit fare revenue hard, and the public transport system now has to be subsidised by taxpayers to the tune of hundreds of millions each year.

But rather than shying away from spending more on a public transport system Perth punters are increasingly avoiding, the McGowan Government is hoping a multi-billion dollar investment will lead to a reversal in fortunes.

WA Labor's Metronet plan. ( Supplied: WA Labor )

By 2023, new train lines will run to Ellenbrook and Perth Airport; Thornlie and Cockburn will be linked; and extensions will also be built to Yanchep and Byford.

All up, the first stage of the Government's Metronet plans including the airport link will cost more than $4 billion — a substantial bet on people rushing back to public transport once the expanded network is up and running.

So, will Metronet be the plan that converts Perth's public transport system from one people like to one more commuters actually want to use?

Ms Saffioti sees no doubt.

"When you build fast, efficient new rail lines and then build very good stations, people flock to public transport," she said.

"When you look at the northern and southern suburbs rail lines, at the time of their construction there was enormous doubt about who was going to use it.

"But they have been enormous successes and you cannot imagine Perth without them now."

The Perth to Mandurah train line opened in late 2007, eight years after legislation passed to allow it. ( Supplied: Peter Major )

Will the passengers come?

If the Government is right about the impact of its Metronet plans, the policy could transform the city and dramatically alter the decades-long reliance Perth people have had on cars.

But if the Government is wrong and people stay away from the new train lines, that huge subsidy taxpayers are now footing to keep the system running would grow dramatically.

The Liberals are worried this could be Metronet's legacy.

"With public transport, you need to hit a particular population density, and I don't think we are there yet," Opposition transport spokeswoman Liza Harvey said.

"There is a little bit of a 'if we build it, they will come' mentality behind Metronet."

Only time will tell if the project will draw enough passengers to make the big investment worth it.

But with billions of taxpayer dollars and a huge slice of political capital staked on it being a policy that transforms the city, the Government will be desperately hoping Metronet brings Perth people back onto public transport.