A rail tunnel between Thirroul and Waterfall could be on the agenda for a Labor government.
The much-talked about tunnel is on a list of options for the party's $2.4 billion transport policy to improve the Wollongong-Sydney rail corridor.
Keira MP and Labor's spokesman for the Illawarra Ryan Park said the tunnel was one of a number of ideas that would be put to an expert rail panel should they win the March election.
Also up for consideration is track straightening in the northern suburbs and the removal of level crossings; there are 24 on the South Coast line.
Mr Park said the list of improvement options was based on Transport for NSW documents received under freedom of information requests.
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He said a tunnel in the northern suburbs appeared a number of times in the government documents, which was why a panel would be asked to assess it and a range of other options.
"The reality is as late as 2017 the Thirroul to Waterfall tunnel, or a tunnel of that nature, is still a part of the mix," Mr Park said.
"In government we would want to make sure [if] it remains part of the mix, [and] if it's part of the long-term mix and doesn’t need funding committed now or is it medium term and something we will have to grapple with sooner rather than later."
Mr Park said the $2.4 billion would be spent on whatever projects the expert panel recommended.
"We will ask them to focus on what we think are the main priorities, give us advice on those and we will allocate funding for what I’d like to see as short, medium and long-term," Mr Park said.
Projects such as track straightening and level crossing removal would likely be short to medium terms projects, he said, while a tunnel would be long term - if the experts recommended it at all.
Labor announced the $2.4 billion promise in early November but then took more than three months to come out with the detail.
Mr Park said the November announcement was because Labor needed to answer questions about whether it would fund the F6 extension.
"Shadow cabinet made a decision that we wanted to say very clearly when we were getting queried about the F6 that it was a project that was not a priority for us, that our project would be rail upgrades," he said.