The Queensland government has announced it will build a new underground for the city, which is estimated to cost $3 billion less than previous plans.

A train and bus tunnel will be built under the Brisbane River as the Newman government’s cut-price alternative to the defunct Cross River Rail project.

The $5 billion Brisbane underground will link Dutton Park and Bowen Hills by a 5.4-kilometre tunnel by 2021.

New stations will be built at Woolloongabba, to service sports fans, and Roma Street and George Street in the city, to service the new government precinct and the university.

The world’s biggest boring machine will dig a 15-metre-wide tunnel to fit two train lines in the lower section and two bus lanes in the upper section.

The project aims to double the city’s train capacity across the river to 48 an hour, remove 200 buses off-inner city streets and get people to work from Beenleigh to the city 14 minutes faster.

Premier Campbell Newman says the project is $3 billion cheaper than Labor’s doomed Cross River Rail project and the council’s Suburbs to City bus link.

Savings were made by boring one tunnel instead of two, taking an inner-city route that is easier to dig, and dumping plans for a Dutton Park station, which required the resumption of 108 properties.

The need for more trains across the river was flagged as far back as 2005, when the former Labor government was warned the Merivale Bridge would hit capacity in 2016.

Projects failed to get up, but Premier Campbell Newman insists his government will follow through.

“I hope I can convey how excited I am,” he said.

“There’s been too much conversation in the past.”

When asked if the state could afford the project, Mr Newman gladly deferred to his treasurer.

Tim Nicholls says Projects Queensland will turn to the private sector to help build the project.

Direct funding from the Commonwealth isn’t expected, but it could be offering private investors a government guarantee to reduce risk.

Infrastructure bonds could also be issued, Mr Nicholls said.

“I’m confident that the finance can be found,” he said.

“We wouldn’t be doing anything to imperil the state’s credit rating.

“There is an appetite in the market for helping government deliver these sorts of projects.”

Opposition Leader Annastacia Palaszczuk expects a cost blow out because of the size of the tunnel and questions whether there would be asset sales or more service cuts.

“It absolutely astounds me that they don’t have the funding details for the proposal,” she said.

“They haven’t said where the money is coming from and I’m very concerned this means one thing, asset sales.”