The 25-chapter business case for south-east Queensland's transformative Cross River Rail project will be finished and given to the Queensland government next month, a senior public servant has confirmed.
That would mean it could be with the national infrastructure prioritisation body, Infrastructure Australia, and then the federal government before the July 2 federal election date.
Building Queensland chief executive David Quinn - who is in charge of preparing the business case for the third iteration of Brisbane's much-needed underground rail project - said June 2016 was his deadline.
"The commitment is to deliver the business case to government by mid-2016 and on that basis that effectively means June," Mr Quinn said.
"It will be up to the government to consider the next steps from there."
He said considerable information was being used from planning from Cross River Rail Mark 1 and from the LNP's BAT tunnel project.
"It would be very inefficient of us to just park that information and start again from scratch."
Building Queensland is an independent infrastructure planning body put in place by the Palaszczuk government to assess and prioritise large Queensland projects.
Mr Quinn said it was wrong to say Cross River Rail had slipped as a high-priority case for Infrastructure Australia.
"The reality is they just haven't seen the business case yet," he said.
"People should not look at that as a negative, it's just part of the process we go through."
The senior public servant agreed there were considerable costs to Greater Brisbane if the project did not go ahead.
"So if the city is going to continue to grow and develop as forecast, we need to look at another city river crossing," he said.
"And clearly Cross River Rail is it."
Transport Minister Stirling Hinchliffe on Wednesday morning told conference delegates that congestion and lost productivity costs in south-east Queensland would slice $69 billion from Brisbane's economic output by 2031 if Cross River Rail did not go ahead.
Mr Quinn repeated concerns raised by Minister Hinchliffe on Wednesday morning that the city's sole inner-city rail bridge was built in 1978.
"And of course the last significant piece of rail infrastructure rail network was the four-tracking of the inner city rail network in 1996," he said.
"So again there is 20 years. There is a significant period of time - a bit over 20 years now and we need to develop that further."
The 10-kilometre long rail corridor with six kilometres of rail tunnel from Boggo Road near Moorooka to the Exhibition Grounds at Bowen Hills is Queensland's No.1 infrastructure project on all state and federal infrastructure lists.
The route has been shifted back to run under Albert Street to Roma Street, despite Albert Street being flooded in the 1972 and in 2011.
Mr Quinn said planners were able to deal with the rare flood issue and Albert Street was a "better catchment for public transport".
"Albert Street Station is seen as a more central location, it's going to provide a better catchment for people as a public transport option."
It will provide 24 train services each hour at peak hours, he said, providing more rail services to the Gold and Sunshine coasts.
"Which is key," he said.
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