The Queensland government says it will be able to fund other projects after Bill Shorten guaranteed to partially bankroll the already Cross River Rail project if Labor wins the next federal election.
The state government had committed to funding the $5.4 billion development alone after failing to secure money from the Turnbull government.
State Treasurer Jackie Trad on Monday said the federal opposition leader's $2.24 billion pledge, which includes $800 million towards the underground construction, would give the state financial wriggle room.
However, Mr Shorten's cash splash hinges on Labor winning the next federal election due next due.
"Bill Shorten's offer of $2.24 billion is a game changer for us," she told reporters.
The Cross River Rail, a 10km of line between Dutton Park and Bowen Hills and four new underground stations at Boggo Road, Woolloongabba, Albert Street and Roma Street, is expected to be complete by 2024.
Existing Dutton Park and Exhibition stations would be upgraded.
Mr Shorten said the initial instalment of $800 million would be paid over three years, starting 2022.
The remaining funding was a 50-50 spilt with the state government over 30 years to repay a yet-to-be finalised public-private partnership deal, to build the above ground section of the line.
"We will also make funding available throughout the life of the project of $58 million a year," Mr Shorten said.
The federal Labor leader did not explain, when asked, why he was pledging the cash despite the project already being fully funded.
Liberal National Party Deputy Leader Tim Mander said state taxpayers would be slugged three times what the government estimates Cross River Rail will cost.
"It's $5.4 billion for the capital costs, $4.5 billion for operating costs over the 30 year program ... and another $4.5 billion for auxiliary projects, things like upgrades of stations," he said.
"The only thing we've heard from the Palaszczuk government is the $5.4 billion capital cost."
Mr Shorten also revealed Labor will match the prime minister's recent $1 billion promise to widen two sections of the M1 between Brisbane and the Gold Coast.