The NSW government announced $1 million in funding for the study in 2018, after engineer Edwin Michell developed a concept plan.

This plan proposed to rebuild the existing rail line between Queanbeyan and Bombala, as well as extending it north to Canberra Airport and south to the Port of Eden for freight and passenger journeys.

But the executive summary of the feasibility study, which estimated the project would cost $6.3 billion, found there would be "little if any, return on investment".

The summary states the proposed 300km railway would pass through challenging terrain and areas of significant environmental value, including national parks.

These constraints mean the project would involve major tunnels and bridges/viaducts, especially between Bombala and Eden and the Canberra Airport connection, that would contribute significantly to the costs.

The summary concludes while there was a "strong amount of community enthusiasm" there was "limited information provided to support the railway".

"The costs of reinstatement of the non-operational railway are significant and the cost to construct the railway down to Port of Eden are extremely high due to the topographical challenges and the environmental constraints," the conclusion states.

"While the sections from Queanbeyan to Bombala to Port of Eden are expensive and difficult to achieve, they could be delivered with a substantial investment."

Cooma and Monaro Progress Association's Richard Hopkins, who is the coordinator for the association's own concept plan for the railway, said the feasibility study contained benefit cost ratios "which appear to be disabling".

"They are disabling if they are valid," he said.

But while he had not been able to view the entire study he believed important features had not been included, including the effect of freeing up congestion for other ports and train lines, which was "critically important".

"One way forward is for an assessment of the Cooma and Monaro Progress Association's concept plan," he said.

He said this "thorough" concept plan puts the cost of a Canberra to Eden railway at $2.9 billion and is available on the association's website.

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