Clash over Melbourne Airport rail design

A new train station will also be constructed at Keilor East and a sky rail bridge built over the M80 Freeway as part of the project.

In a statement, a Melbourne Airport representative said airport officials were yet to come to an agreement with the state government on the location or design of the airport connection.

"Melbourne Airport's preference has been, and remains, an underground station," airport ground transport chief Jai McDermott said.

"(It) provides a superior passenger experience, safeguards for future connectivity and is appropriate for Victoria's international gateway.

"It is important that the new rail station works for all airport users, not just those who arrive by train."

The business case, released on Wednesday, found the project will cost between $8 billion and $13 billion and would have a benefit-cost ratio of up to $2.10 for every $1 spent.

It said building an elevated station at the site would be quicker and less expensive to build, while there would be less of an impact on passengers during construction.

The Victorian and Australian governments are each contributing $5 billion towards the project. 

Minster for Transport Infrastructure Jacinta Allan said the new station is a major win for residents living in Melbourne's growing western suburbs.

"The new station at Keilor East means airport rail will truly be a new rail line for Melbourne's west, connecting hundreds of thousands of people to Melbourne's train network for the first time," Minister Allan said in a statement. 

"This project stacks up. Not only will it better connect Victorians to our city, our suburbs and the world –it will repay every cent invested in opportunities for local workers and businesses."

The state government says trains between the city and airport would run every ten minutes and the journey would take around 30 minutes when the project is finished in 2029.

It would also include 12 kilometres of extra track and an upgrade to Sunshine station.