Businesses in Brisbane's CBD could be taxed more to help pay for the proposed $5.2 billion Cross River Rail project just "for the privilege of being next to it".

Acting Premier Jackie Trad says one of the “innovative funding models” being considered to help pay for a second river rail crossing in Brisbane is “value capture”, similar to that used for London’s Crossrail, which takes advantage of increased property values in areas surrounding the infrastructure project.

“That is where areas around the particular area of the infrastructure project get to pay a contribution, because they get value uplift in terms of their properties, in terms of their businesses,” Ms Trad told ABC Radio.

“Now it’s very much in its infancy.

“We are looking at how we can actually identify those areas that will be ready for development, where businesses can be placed and flourished and how they can contribute to the actual delivery of this infrastructure project.”

But the plan already has its critics, with Graham Young, the executive director for conservative think tank Australian Institute for Progress, suggesting the idea was a “souped-up land tax”.

“I’d argue that it’s completely illegitimate, because if there’s an increase in the value of the land around the infrastructure then it ought to be reflected in the valuation of the land, so it would have come through in land tax and things like that,” Mr Young, a former Liberal Party staffer and candidate, said.

“You shouldn’t be hitting people over the head.”

Mr Young said those whose properties will be resumed for the project were lucky, because they’d be compensated.

“The unlucky ones are the people who happen to be next to it and it sounds like they’re going to get even more unlucky, because Jackie’s going to charge them for the privilege of being next to it.”

The possible funding idea comes after Ms Trad on Thursday said the project’s business case wasn’t due to be finished until mid-year.

She was also unable to say what the funding split would look like between tiers of government and wouldn’t rule out increasing state borrowings and debt to pay for the new rail line.