Professor Barbara Norman will argue the case in favour of the tram, describing it as an crucial project that will "reboot" and shape Canberra's development into the future.

The forum, in the city at lunchtime, has been organised by former Labor chief minister Jon Stanhope, who says he will not "take sides" on the debate.

"This is a very lively debate. It's captured the imagination of the people of Canberra, there are two very polarised views being expressed publicly ... and it's quite clearly going to be a significant issue over the coming year in the lead-up to the election," he said.

Mr Stanhope confirmed light rail was in the agenda at various times while he was chief minister but the case never stacked up.

"All the evidence presented to me when I was chief minister and the business cases that we developed didn't encourage investment in light rail at that time. But certainly the situation may have changed since," he said.

Economist Mr Hughes, former manager of major project analysis for ACT Treasury, has described the tram as a folly and the business case as a fantasy.

He said the government's own reports showed the project didn't make sense on economic or transport grounds, making little difference to patronage or transport times, and not delivering sufficient transport benefits to justify the cost.

"We know from the government's own work that it doesn't really make sense as a transport project. The recent conclusion in the environmental impact statement that it's effect in travel time and congestion and delays is negligible. It's going to cost more than it brings in transport benefits – its own cost-benefit studies confirm that. All we are left with is claims about the wider economic benefits which are completely unsubstantiated and implausible."

But Professor Norman, head of urban and regional planning at the University of Canberra, said the tram was the beginning of improving public transport across the entire city. The tram was a very efficient way of moving people quickly, and the first stage would bring efficient, off-road mass public transport to Canberra.

She said the debate was not about light rail or the status quo because doing nothing was not an option, with Infrastructure Australia estimating the cost of congestion in Canberra at $208 million in 2011, rising to $703 million by 2031.

"If you don't want the light rail then the question is what is the alternative? From my planning perspective, building an efficient light rail is much more preferable than, for example, building another freeway through the northern suburbs which would have much more significant social, environmental and economic costs."

The message of the Gungahlin Drive extension through Aranda was clear.

"It is not the solution to build another freeway which will simply fill up with cars again, but to build an efficient modern mass transit system is definitely the way to go," she said, pointing also to the reduction in greenhouse gas emissions it would bring.

"I think a broader view of cost benefit analysis is required when we're making these big public investment decisions," she said, pointing to the tram as a way of re-shaping Canberra for the future and providing new opportunities for sustainable economic development.