Prime Minister Tony Abbott will hand over $1.5 billion in federal funding for the east-west link without seeing the full business case for the controversial massive infrastructure project, despite an election promise that any investment of more than $100 million would require a published cost benefit analysis.

Confirming he would honour the coalition's election commitment to partly fund the $8 billion Victorian government tollway, which would connect the Eastern Freeway to Melbourne's western suburbs, Mr Abbott told radio station 3AW that he trusts that the East West Link is a viable project despite not being provided with the full business case, which the state government has refused to make public.

The Royal Park exit of the proposed east-west tunnel.

Premier Denis Napthine has defended the lack of transparency, saying that the the public release of details would place in jeopardy a competitive advantage as it sought bidders for its construction.

Instead, the government has released a brochure asserting the project will generate $1.40 in benefits for every $1 invested.