The Andrews government re-affirmed its preferred alignment for the 90-kilometre ring from Cheltenham to Werribee on Tuesday, while announcing the authority which will discuss station locations with relevant groups.

"This dedicated new authority will ensure the biggest public transport project in our state's history becomes a reality," Premier Daniel Andrews said on Tuesday.

The loop will connect to an airport rail and create three transport super hubs at Clayton, Broadmeadows and Sunshine.

The geotechnical works are underway and registration of interest for firms to build the project are still open.

It is not known if any properties will need to be acquired to build the stations with the premier flagging he hoped to minimise the impact on local residents.

Despite a federal government $475 million pledge for rail links between Monash University's Caulfield and Clayton campuses, Mr Andrews said his rail loop was the priority project.

"You can't proceed with that project and ignore the fact that the suburban rail loop is being built as well," Mr Andrews said, while standing at the university's Clayton campus.

"The two need to work together well, and that is why we are committing to continuing to do the business case development."

Opposition Leader Michael O'Brien says the suburban rail loop project won't just tie up future governments but also future generations.

"This is lines on a map and he's spent more money on spin doctors and he isn't even building anything," Mr O'Brien told reporters on Tuesday.

"Daniel Andrews is taking Victorians for a ride but it's just not on a train at the moment."

Construction on the loop is expected to begin in 2022 and could take up to 30 years.

Rating agency Moody's released a report in July cautioning Australian states against rising debt, and singled out the suburban rail loop as a "challenge" to the state's finances.

But the government says it's confident the state would retain its triple-A credit rating.

Australian Associated Press