While the South Coast rail line to Sydney is one of the most sensible in terms of an upgrade, its benefits have been overstated - and improving connections within Sydney would have a bigger pay-off.
The Grattan Institute analysis also poured water on the long-held dreams of high-speed rail along the east coast, saying it's not realistic and a waste of money.
The Fast Train Fever report found the Wollongong-Sydney commuter line ranked third out of all regional lines when it came to the number of passengers, with more than 19,000 commuters.
Only regional lines in the Gold Coast (28,528 commuters) and the NSW Central Coast (25,059) were higher.
The report found that upgrades to the South Coast line and the Gold Coast "would lead to the most feasible commutes".
But the report opposed several commonly-held ideas, including that a one-hour commute to Sydney would see more people catching the train.
While those already on the train would benefit from a faster service, those driving to Sydney would likely continue to do so.
"Most metropolitan jobs aren't in the CBD. In Sydney and Melbourne, about 15 per cent of jobs are in the CBD," the report stated.
"That dispersion of jobs explains in large part why most people drive to work. While most CBD commuters take public transport, most commuters to anywhere else in the city drive to work.
"It's the same for regional commuters. Most work in the suburbs, not the CBD. And people who are commuting from regional cities are only taking public transport if they work in the CBD."
The NSW government's planned rail upgrades for the South Coast line are aimed at moving towards a 60-minute trip. The Grattan report noted that would be equal to if not better than the CBD commute from some of Sydney's outer suburbs.
Improving those outer Sydney services would be more beneficial than upgrades to the South Coast line, the report found.
"Because of the numbers of people affected, improving outer-suburban public transport and suburban black-spots can make commuting to jobs beyond the local area more feasible for a much larger number of people than regional rail renovations," the report stated.