Dismissing analysis of the first stage city-to-Gungahlin line included in Monday's Productivity Commission report on public infrastructure, the Capital Metro Minister said up-to-date city building benefits would be made clear in the project's final business case.

The government is believed to have a draft of the document, including cost-benefit analysis and passenger projections for the $614 million project.

It will replace existing information included in an unsuccessful Infrastructure Australia submission prepared in August 2012.

A final version of the business case is due to be considered by the cabinet in October.

Mr Corbell said the authors of the Productivity Commission report did not seek updated information from the Capital Metro agency before finding the government had not justified the cost of the line, which is the first stage of a proposed city-wide network.

"As the Productivity Commission says itself in the report, factors beyond economic ones need to be considered by the government,'' he said.

"I am disappointed that the commission did not ask the government what its broader rationale was beyond economics for determining support for this project because if they had asked us, we would have talked about the broader social benefits, active transport, integration of public transport into the light rail corridor in a way that buses cannot deliver."

Mr Corbell said the economic return would outweigh the cost, and social and economic benefits could not be delivered by improved bus services as recommended by the report.

"We know that putting buses down Northbourne Avenue means either taking away two lanes of traffic or building roadway down the middle of the median strip. Neither of those outcomes are acceptable for the city,'' he said.

Opposition transport spokesman Alistair Coe said there was no economic justification for the tram line, which has a projected 25-minute travel time.

"The original decision making process for light rail was flawed,'' Mr Coe said. ''At the time of the government making their original decision to go ahead with light rail, the evidence did not support it and that's what the Productivity Commission is critical of.''

Canberra Urban and Regional Futures researcher David Flannery identified the increase in nearby land values and the money saved on greenfield infrastructure through higher density as key contributing factors supporting the tram line.

He said considering only the economic cost of public transport infrastructure was too simplistic and had distorted public debate.

"Many of the health and planning and social benefits are intangible,'' Mr Flannery said. ''An economic cost analysis like the Productivity Commission has done doesn't even think about all this sort of stuff.

"The commission wouldn't have considered at all benefits in savings in stopping or slowing down urban sprawl. It's huge."

An advocate of light rail for Canberra, Mr Flannery said Melbourne's tramway development in the 1880s had come when its population was equivalent to Canberra in 2014.

"It's the city in the world that has the largest tram network. Melbourne is an international icon for a tramway and it brings so much national and international kudos to the city, and it's sustainable," he said.

"More than 130 years later, it's still the present that keeps on giving."

Mr Corbell is yet to outline which aspects of the final business case will be publicly released after consideration by the government.