A fast rail plan that would cut the Wollongong-Sydney travel time by more than half is under investigation by the federal government.
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This is despite rejecting the South Coast line in favour of Newcastle for faster rail last year.
The initial funding $20 million for the Faster Rail project has been boosted to $40 million.
That is to allow the development of business cases for five more fast rail corridors - one of which is the Wollongong-Sydney link.
A link between Sydney and Parkes is also under consideration.
A spokesman suggested the top speed of the fast rail would be around 160km/h, which would reduce the Wollongong-Sydney travel time to around 31 minutes.
The business cases are not a guarantee that faster trains will become a reality in the Illawarra; the research will be used to determine future priorities for funding and construction.
Prime Minister Scott Morrison said the Faster Rail idea was, like cuts to immigration, about finding ways to deal with congestion.
The top speed of the fast rail would be around 160km/h, which would reduce the travel time to around 31 minutes.
"This is all part of our plan to manage population growth that I announced this week to take the pressure off our big cities like Sydney and make our regional cities like Wollongong, Newcastle and Parkes even more attractive places to live and work," Mr Morrison said.
"As our population grows, fast rail networks are crucial to easing the congestion pressures in our cities and shaping Australia's future."
Infrastructure Minister Alan Tudge said the plan would make better use of regional centres.
"Fast rail from the big capitals to the regional cities eases the pressure off the big cities while supporting the growth of the regions," Mr Tudge said.
In 2017, Transport for NSW had put forward the South Coast line as one of three funding options under the Faster Rail program, but it was knocked back on a federal level.
The government instead opted for the Sydney-Newcastle line; a Transport for NSW spokesman said at the time it was judged as "best fitting the funding criteria under its Faster Rail Prospectus process".
The federal government plan is distinct from the Berejiklian government announcement of faster rail for the Illawarra made in December last year.