Only a small proportion of Canberra's population would be properly served by the city's proposed light rail project, calling into question the scheme's viability, the ACT Opposition has said.

The ACT Government plans to build the Capital Metro light rail project from Civic to Gungahlin at a cost of about $614 million.

The Opposition said analysis of 2011 census data showed about 7,000 people lived within a distance of a stop that meant they would be likely to use the service.

But Minister for Capital Metro Simon Corbell said the Liberals' analysis did not take into account projected growth along the route.

Stage one of the project will link Gungahlin and the city using a track which runs along the centre of Northbourne Avenue.

The Opposition said the figures showed 27,000 people lived within 800 metres of the proposed stations.

A further 12,000 people would have a light rail stop within 400 metres of their home, but the Opposition concluded that would include 5,000 people in the city catchment area who would be unlikely to use the service.

Opposition transport spokesman Alistair Coe told 666 ABC Canberra that was not enough patronage to make the $600 million project viable.

"One way or another you're looking at a very small proportion of Canberra's population that are going to be serviced properly by light rail and for that reason we've got real doubts about this project," he said.

"One of the issues with going beyond 400 metres is the patronage really does start to fall away quickly.

"Given more than 90 per cent of Canberra's population will still need cars, buses or bicycles, the project will hardly be transformational as over-promised by the Government."

Mr Coe said buses provided a more flexible service.

"It's not to say that Action buses are running the way they should right now but I think Action buses will have far more flexibility and will have far more capacity going into the future than a rigid light rail system."

ACT Government rejects analysis, points to population growth

Mr Corbell rejected the Liberals' analysis, describing it as simplistic.

"The population in the Gungahlin to city corridor will grow from around 43,000 people in 2012 to over 61,000 people in 2031," he said.

"The number of jobs in the corridor will grow from 59,000 in 2012 to nearly 73,000 in 2031.

"That's simply not part of the figures that the Liberals have put out."

Mr Corbell said the Liberals' analysis also did not take into account people who use park and ride facilities, or cycle to work.

"For our city we know that light rail is the best choice, the best choice because it returns more back into the economy than it costs to deliver," he said.

'It's a better choice in terms of the corridor itself because it fits into the beautiful landscape quality of the corridor, buses will never be able to do that, and it meets that long-term growth in population."