A key State Government MP wants tolls on the Mitchell and Kwinana freeways to help pay for their maintenance and encourage more use of public transport.

Liberal MLC Jim Chown, parliamentary secretary to Transport Minister Dean Nalder, called for greater consideration of tolls in WA after looking at user-pays road systems in Greece.

Mr Chown was one of five Liberal MPs who billed taxpayers more than $55,000 to visit Athens in July at the same time for varying reasons, including an Anzac study tour and inspecting underground rail and Greece's parliamentary system.

In his report on his trip, tabled in Parliament this week, Mr Chown wrote that Greece's toll road system run by private enterprise supplied "state-of-the-art motorways" in metropolitan and country areas.

"Greece has had a user-pays ideology in terms of toll roads in their country since 1927, which is one that I believe requires further consideration in WA," he wrote.

Citing a population increase of 75,000 in WA last year and heavy freight movements, Mr Chown wrote that the need for "evermore upgrades and annual expenditure upon upkeep are of major concern to the State of WA".

"A user-pays system on the two major arterial freeways into Perth would go towards the upkeep of those freeways and would also go towards encouraging road users on to public transport to ease traffic congestion," he said.

This year the Government began investigating whether to impose a freight-only toll on the future Perth Freight Link, a highway linking the airport precinct with Fremantle port, but ruled out tolls for private vehicles.

But shadow transport minister Ken Travers said: "Mr Nalder's second in charge has let the cat out of the bag."

He said the Government was responsible for more heavy freight on the roads by closing Wheatbelt rail lines, and wanted to use that as an excuse to introduce tolls.

Mr Nalder said the Government had "no appetite" for charging a toll for standard cars.

"We don't want mums and dads paying a toll to use the roads," he said. "It is absolutely appropriate for the parliamentary secretary to be investigating different transport systems and how they operate, and reporting to Parliament on what (he has) learnt."