The route for the proposed BaT Tunnel has changed, meaning it will be four kilometres long and run from Dutton Park to Spring Hill with new underground stations at Woolloongabba, George St and Roma St.

In what is set to be one of its drawcards ahead of next year's state election, the government wants to knock down the Transit Centre building in 2016 and complete the entire BaT project by 2021.

However it is yet to ink a deal with the Transit Centre owners, which include Lend Lease and other associates. On Sunday, Premier Campbell Newman said it would cost at least $100 million to acquire the site.

"They've been trying to sell it for a while so we hope they've got a sharp pencil. We've got a sharp pencil too," Mr Newman said.

Despite the large outlay the Premier said the new design of the BaT Tunnel would save "hundreds of millions of dollars" due to reduced tunnelling and re-engineering.

"The current overall cost of this is $5 billion. We've got to pull a lot of money out of that because we've got to make it more affordable for this state," he said.

The government has already set aside $1 billion from asset sales and leases, however it plans on splitting the rest of the cost with the private sector.

Opposition leader Annastacia Palaszczuk criticised the government for not releasing the full business case for the BaT project.

"We know that it is unfunded and uncosted. We need to make sure Queenslanders see the full cost here. They need to release the business plan," she said.

"We are back to the drawing board with this BaT Tunnel, and once again regional Queensland is missing out."

Ms Palaszczuk said a Labor government would create an independent body named Building Queensland to best decide on future state infrastructure projects.

The government hinted at changes to the BaT design months ago, having already reversed an idea to axe the Dutton Park train station.

"I think there are more things that can be done to minimise the footprint – if I can put it that way – to deliver the outcome," Mr Newman told reporters on September 2.

Transport Minister Scott Emerson confirmed Roma St Station commuters would be affected during any construction work, and the Department of Transport and Main Roads would work with bus operators to relocate a long-distance bus centre.

"The Transit Centre is frequently voted as one of Brisbane's ugliest buildings, but now we have the chance to build an iconic gateway to this city," he said.

The plans were also supported by Brisbane Lord Mayor Graham Quirk, who joined Mr Newman and Mr Emerson for the announcement at the Roma St Station on Sunday morning.

Public consultation on the new design is open until December 19.