A new leaked report has backed the case for an inland rail link from Wollongong to south-west Sydney.

It is the second report in a week to back completion of the Maldon to Dombarton rail link.

The 35km line was partially built in the 1980s then abandoned as a cost saving measure, but the rail corridor remains in place.

A report released by the University of Wollongong's SMART Infrastructure Facility on Tuesday found the project would cost $1.7 billion to build, but would return a gross regional product benefit of $2.6 billion.

The report calculated a benefit-cost ratio of about 1.56 (on a net present value of 7 per cent over 50 years), and estimates 1,100 equivalent full-time jobs would be created in an area of high unemployment.

A second report prepared by Transport for NSW seen by the ABC backs up the SMART report.

Rail link would bring significant benefits, report finds

The Maldon to Dombarton Final Business Case report produced in the past four years calculates a benefit-cost ratio of about 1.5.

The general rule of thumb is that if the benefit is higher than the cost of the project, it is a good investment.

The Transport for NSW document calculates the total cost at about $1.3 billion, made up of about $730 million in capital costs and $620 million in recurrent costs.

It also calculates significant social and environment benefits.

They includes time savings worth about $900 million, avoiding $190 million in crash costs and preventing road damage worth $370 million.

Transport Minister Andrew Constance has vowed to look at the case for the rail project as part of his Government's future transport planning for NSW.

"I am very conscious of the community effort that is underway to see better connectivity to Sydney," he said.

"And of course part of this is making sure we align the freight strategy for the region and its future very much in a way that enables fulfilment of requirements when it comes to passenger rail as well."

Both reports indicate that opening up the inland route would free freight from the coastal South Coast line to enable an increase in passenger services and improved timetables for tens of thousands of daily commuters.

Reducing pressure on road and rail

Rail expert Philip Laird visits the partially built Maldon Dombarton Bridge south of Picton. ( ABC News )

Rail expert Philip Laird, from the University of Wollongong, said the completion of the line could not come soon enough, with growing pressure on rail and Mount Ousley Road, the main transport link out of Wollongong.

"Mount Ousley now has nearly 7,000 trucks per day. That's 13 per cent of over 50,000 vehicles a day using the road," he said.

Dr Laird said the rail line was also overburdened with freight.

"If we want more passenger trains, we've simply got to get some of those freight trains off the South Coast line and onto Maldon Dombarton," he said.