The Victorian Treasurer will not release the business case for a planned multi-billion dollar tunnel project.

Victorian Treasurer Michael O'Brien has rejected calls to justify the spending of large sums to build the East West Link tunnel.

The project includes a 12 kilometre tunnel to connect two major arterial roads, saving time for some residents travelling across the city.

The call for numbers underpinning the plan have come after one authority said early costs would outstrip the later benefits.

Infrastructure Australia has told a Senate committee the cost of building and operating the road would be considerably higher than the economic benefits, if the project is assessed by the standard analysis method.

The Victorian Opposition says this means the Government either has its own assessment method, or it knows that the big dig will not be worthwhile.

“If the Government is so confident in the way in which it has assessed this tunnel in what it says is the economic and utility benefits for Victorians, then it should release the business case,” said Labor member for Altona Jill Hennessy.

The Government has released an executive summary of the business case, but the Treasurer says the rest contains commercial-in-confidence information.

“You've got three international consortia all bidding for the right to build East West Link,” he said.

“If we released all the commercially sensitive information now while the bidding's going on, that would only help those companies and ultimately it would cost taxpayers more.”

He also says the analysis does not include the flow-on effects of the project, including the jobs it creates.

Preliminary tests have been undertaken for the first phase of the project; a six-kilometre roadway connecting Melbourne’s Eastern Freeway and CityLink roads.

The test-sites have been the subject of ongoing protests by residents, who argue that the same problems could be more effectively solved for less by spending on public transport.