The council believes variable pricing could be one way to keep congestion in the CBD down - and wants the government to be able to impose it without having to renegotiate contracts with the $24 billion toll road operator.

The call comes as a Senate report into Australian toll roads, completed by a Labor-led committee, finds that secrecy in government deals to build privatised motorway projects is eroding public trust.

On Tuesday, five weeks of environmental impact hearings wrapped up into the West Gate Tunnel, a $5.5 billion toll road through Melbourne's west that Transurban successfully pitched to the Andrews government behind closed doors.

The government and Transurban want to start work in 2018, and are expected to agree on what motorists will be chargedby the end of this year.

The West Gate Tunnel will likely end up with similar prices to Transurban's other Melbourne toll road CityLink, which charges cars more than $9 from start to finish.

CityLink earned Transurban revenue of $687 million last year.

Melbourne City Council opposes key aspects of the project, which will see the West Gate freeway widened to 12 lanes, a tunnel built under Yarraville, and city-bound off-ramps dumping 9000 extra cars daily into West and North Melbourne.

On Tuesday the council proposed that the planning minister should be able to occasionally review the toll road's prices and direct Transurban to raise them to discourage traffic.

The council's barrister at the hearings, Nick Tweedie, SC, said the public regulation of tolls was a "very effective and transparent and desirable" way to limit the environmental damage caused by congestion.

???The planning minister should control tolling, Mr Tweedie told the committee.

"He could tell them, 'Look, we've got a problem with congestion at 8 to 9 in the morning; we need you to implement a variable toll which encourages people to travel either before 8am or after 9am'."

Mr Tweedie said the idea was both effective and legal, comparing it with ministers giving directions to where storm water flows or how many gaming machines might operate in a municipality.

Questioned whether granting the minister power over pricing would kill Transurban's interest in the project, Mr Tweedie said it wasn't for the inquiry to speculate on what a private operator might or might not do.

"Your concerns should be only this: is this a mechanism that is likely to achieve or the potential to achieve public good and good environmental outcomes?" he said. "It's clear that it will."

But Stuart Morris, QC, for the government's Western Distributor Authority, said it would be "novel" to give the planning minister the power to set prices over traffic, as well as being legally questionable and outside the inquiry's scope.

A spokesman for Treasurer Tim Pallas said negotiations between the government and Transurban would "obtain the best outcome for Victorians".

Transurban - which controls 13 of Australia's 16 toll roads - has a contract with the Victorian government dictating the prices it can charge to use the road.

The government must propose a costly renegotiation of the contract if it wants to change the tolling structure.

Anita Orr, from Transurban, said tolling arrangements would be set by the government.

Under the proposed deal for the road, about $3.8 billion of the $5.5 billion cost of building the proposed road is to be paid by Transurban. In return, the Andrews government would extend Transurban's right to toll CityLink until at least 2045.

Meanwhile, the Senate has released a report following its investigation into the operation of existing and proposed toll roads in Australia.

Among its findings was that the commercial nature of past toll road projects had "created a case for commercial confidentiality which makes it difficult to ensure that the process is as transparent as possible and to maintain public trust".

One senator on the inquiry, the Greens' Janet Rice, said too many toll roads were being governed or built in secrecy.

"This report indicates that decisions on significant transport projects are being made in the interests of private transport companies rather than in the interest of the public," she said.

The report was authored by seven senators, three of whom - including the chair - were Labor.