The New South Wales government is accused of jumping the gun by announcing Australia's longest road tunnel through the Blue Mountains without locking in all the funding.
The state opposition and some residents in the Hartley Valley have questioned where the money would come from.
The state government projected the entire 34km upgrade, including the 11km underground stretch from Blackheath to Little Hartley, would cost $8 billion.
It committed $2.5 billion for the project, and the Commonwealth has locked in $2 billion, but its share is not to be used for the underground section.
That means $3.5 billion towards the cost of the works is currently not accounted for and there is no firm price tag on the toll-free tunnel.
The ABC has sought clarification on what portion of the bill either level of government would stump up, after the Minister for Regional Roads and Transport Sam Farraway, and Deputy Premier Paul Toole, locked in the multi-billion dollar works on Sunday.
Budget pressures raise questions
Shadow roads minister John Graham said it came at a time when cuts to other projects were taking place, ahead of the 2023-24 budget.
"Due to rising cost pressures on the transport side of the budget some of the projects which have been promised across the state will be slowed down," Mr Graham said.
He said that included Parramatta Light Rail Stage 2, Sydney Metro Southwest and the Beaches Link.
"At the same time to have another big promise — the longest tunnel we've seen in NSW — without funding clarity, it really leaves a question mark about how serious this promise is and whether it'll be delivered and when it'll be delivered," he said.
Mr Graham expected the project to blow out beyond the $8 billion budgeted due to the difficult nature of long tunnelling work through sensitive heritage and wilderness areas.
The design would see engineers dig about 100m under Mt Victoria and 30m under Blackheath.
"From the people I've spoken to in the construction industry, I don't believe that the government's forecast is very credible."
The community of Medlow Bath has also called for the tunnel to be 19km, starting at Katoomba, an option which the Member for Macquarie Susan Templeman wants considered.
A long way away
The tunnel plan concerns some residents of the Hartley Valley who fear there is a lack of ventilation planning for the infrastructure, which could result in pollution sitting among the historic landscape.
Treasurer of the Hartley District Progress Association Ramsay Moody described the project as being a "disaster" for the area.
"One of the major issues of course is the flow of exhaust gases into the Hartley Valley, particularly from the westbound tunnel," Mr Moody said.
Work to formalise the design of the tunnel is still underway and the Environment Impact Statement is being prepared.
"It's got a lot of environmental issues associated with it that have still got to come out into the public domain," he said.
"It's totally unfunded at this stage so it's got a long way to go yet."
In a statement, Transport for NSW Director West Alistair Lunn said the tunnel "is going to transform travel between the east and the west, reduce congestion and improve safety for residents, tourists and our freight industry".
It is estimated the tunnel could reduce travel time by up to 30 minutes.
Mr Lunn said air quality and human health were priorities when designing tunnels and the team was working with the NSW Chief Scientist and Chief Health Officer.
The ABC contacted Deputy Premier Paul Toole and federal Minister for Infrastructure, Transport and Regional Development for comment.
Construction on the tunnel is set to commence in 2024 and finish by 2027.
