Canberra months from Melb Metro decision

The federal government is likely months away from deciding how much it might contribute to the $10.9 billion Melbourne Metro Rail project.

Federal Major Projects Minister Paul Fletcher and federal Transport Minister Darren Chester will meet with Victorian Public Transport Minister Jacinta Allan in Canberra next week to continue negotiations.

Ms Allan wants Victoria and the federal government to be "equal partners" in the project with both putting up $4.5 billion.

But she conceded on Wednesday that part of Victoria's own contribution would come from a federal-government grant originally intended for the dumped East West Link tollway.

"(Victoria's) $4.5 billion includes the $1.5 billion that was in last year's state budget," the state minister told reporters.

Mr Fletcher said the Commonwealth would have Infrastructure Australia carry out a detailed assessment of the business case that was released on Tuesday.

That's expected to take "some months", the federal minister said on Wednesday.

"We are not in the business, unsurprisingly, of handing over a cheque for $4.5 billion just because we are asked for it," he said on 3AW.

The business case shows a $1.10 return for every dollar put into the project, increasing to $1.50 when wider economic benefits are taken into account.

Melbourne Metro Rail will allow the network to hold 39,000 extra passengers in peak periods through the creation of twin tunnels under the CBD.

Ms Allan on Wednesday wouldn't speculate on how the project would be funded if Canberra didn't contribute enough funds.

"I'm not going to pre-empt any negotiations we will have with the federal government until I've sat down with federal ministers and federal colleagues," she said.

The Victorian government hopes major construction work will commence in 2018.