The business case for the Sydney to Newcastle link of the east coast high speed rail project is scheduled to be finished in 2026.
High Speed Rail Authority acting chief executive Andrew Hyles told a recent infrastructure summit that the link would have a transformative impact on the Hunter Region.
"The Sydney to Newcastle corridor has the largest regional passenger volume in Australia," he said.
"The corridor is already at capacity, so there's got to be some kind of solution to that."
It is estimated that a high-speed rail link would cut the 2 hour 30 minute commute from Newcastle to Sydney to between 45 to 50 minutes.
This, in turn, would free up space on the existing corridor and attract new rail commuters.
"Doing nothing on that corridor is not an option," Mr Hyles told the Australasian Railway Association's conference.
However, the heavily urbanised nature of the route, combined with challenging terrain around Hawkesbury River, meant parts of the Sydney-Newcastle route would require tunnels, which can cost more than $1 billion a kilometre.
The High Speed Rail Authority has been allocated $13.58 million across three years to plan the Newcastle and Sydney connection.
It followed a $500 million commitment from the federal government in 2022 for planning and corridor acquisition between Newcastle and Sydney.
Mr Hyles conceded the cost of the entire Melbourne to Brisbane line would cost more than the federal government's last official estimate of $114 billion.
He said recent projects overseas had cost $100 million to $200 million a kilometre. Given the distance between Melbourne and Brisbane is around 1800 kilometres, the figures imply a cost of $180 billion to $360 billion.
"I acknowledge that there is scepticism about building high speed rail in Australia and it will not be quick or easy," Mr Hyles said.
"Constructing high speed rail has a high cost no matter where it's built around the world, and Australia will be no different."
He said a "range of key issues" still had to be resolved to make high speed rail a reality, and it was essential to get the planning right to protect against potential future unexpected cost increases and time delays.
Mr Hyles also said much had changed since the government released its 2013 High Speed Rail report and a number of assumptions contained in it were no longer current.
The High Speed Rail Authority is working towards delivering its Pathway to Delivery in 2025.
The report will include information about station locations, patronage forecasts, financial estimates and timeframes for delivery.
The 2018 report, which was never released, investigated four high-speed routes out of Sydney, north to Newcastle, south to Nowra via Wollongong, south-west to Canberra and west to Orange.
Professor McNaughton said 250kmh rail services to Newcastle and Wollongong would "change the face of NSW".
"In my book, you've got to fix the corridor between Sydney and the Hunter," he said.
"That [would make] the biggest difference to the biggest number of people."
