The Premier Denis Napthine has defended traffic projections, justifying the business case for Melbourne's East West Link.
In leaked cabinet reports which appear in Fairfax Media it has been revealed travel predictions for the road were boosted by as much as 15 per cent.
That is on the basis that rising wealth will encourage more people to use toll roads to avoid wasting time by sitting in traffic.
Dr Napthine has told Fairfax Radio people will be willing to pay to use the road.
"We expect that people will increasingly value their time, people will increasingly not want to be caught in congestion," he said.
"So this project is about reducing congestion, improving efficiency in transport and that people will be prepared to pay for that."
The opposition says traffic projections justifying the business case for the link are shonky.
Shadow Minister for Infrastructure, Brian Tee, says the document's figures are suspect.
"What they clearly show is that this modelling has never been used before, it's shonky," he said.
"It achieves the outcome that the Premier wants rather than has an honest look at the merits of this project."