''Can we afford not to build it when we have 100,000 people out at Gungahlin and surrounds?'' asks Barbara Norman, professor of urban and regional planning at the University of Canberra.

Building the 13-kilometre line is part of the agreement ACT Labor reached with the Greens to form minority government.

The link is estimated to cost more than $600 million but the final cost will not be known until a winning bid is selected. Work is due to begin in 2016, will take two to three years to complete and may be followed by other legs, once the city's light-rail masterplan is complete. Light rail is being retrofitted to some cities after being pulled out years ago. In Sydney this week the light rail extension began operating from Lilyfield to Dulwich Hill.

Professor Norman described the introduction of light rail as a very positive step for the national capital.

"I think we can afford it if we consider the long-term benefits to the community as well as the initial costs,'' she said.

"If we take a broader view and a long-term view about our cost-benefit analysis, I think it will be shown to be a significant positive contribution to the community.''

The project is being run by Emma Thomas, project director at the Capital Metro Agency, who says her job has been made easier by the wide boulevards drawn up by Walter Burley Griffin when heavy rail was the usual mode of public transport.

''What makes that fantastic is that unlike other cities we already have those corridors well protected,'' she said. To Gungahlin, ''we have a really wide corridor, it's been set up for us''.

Ms Thomas said light rail would move commuters quickly from Gungahlin, which was growing at five times the rate of any area in the ACT.

In Canberra, ''we have a car addiction that is quite significant compared to the rest of Australia - part of that is our city design'', she said.

Ms Thomas sees an opportunity to redevelop Northbourne Avenue, as property values are expected to rise along the rail corridor.

''For me as someone new to Canberra and really enjoying it, having that community housing in our face on Northbourne Avenue in the state that it's in - it needs some sort of uplift, it's almost like a slum that Canberra has set up in the middle of the city,'' she said.

The ACT Liberals have questioned why Ms Thomas would receive the same salary as the head of the Chief Minister and Treasury Directorate.

Liberal MLA Alistair Coe remains sceptical of building light rail, at least from Gungahlin.

''Even at the provisional cost of $614 million, that would be by far the single biggest capital works project the ACT government has embarked on, and to commit to such a project with such little knowledge of the economics, I think is very risky.''

Mr Coe said he was concerned the ACT government might spend so much money on the first leg of the project that light rail might not be extended to other parts of Canberra.

Light rail running from Belconnen through the city and Russell to the airport would generate demand in both directions.

''There are employment hubs at both ends of the route and therefore you would have people going in the train in both directions,'' Mr Coe said. He is concerned the popular Red Rapid bus would be stopped when light rail begins operating.

Ms Thomas said on Friday her agency was working with Action to ensure buses and light rail could provide the best possible service.

''Typically, it would make sense to avoid running buses and light rail along exactly the same route, but they will certainly share some space and connect along the Stage 1 City to Gungahlin corridor, as light rail adds to the high-quality services already provided by Action,'' she said.