The Grattan Institute's analysis also found that improving connections within Sydney would have a bigger pay-off.

But a UOW transport expert disagrees, saying there "should be no doubt at all" that faster trains between Wollongong and Sydney would benefit both regions.

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 for work would likely continue to do so, citing that only 15 per cent of jobs were in the CBD.

"That dispersion of jobs explains in large part why most people drive to work," the report stated.

"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 Grattan report also claimed improving the commute from some of Sydney's outer suburbs would benefit more people than an upgrade of the South Coast line.

UOW's Professor Philip Laird said the report overlooked examples of where rail upgrades had benefited regional areas.

"For speeding up regional train speeds, the report appears to overlook the benefits of what Victoria has gained with regional fast rail," Professor Laird said.

"More and faster trains have allowed cities such as Bendigo and Ballarat to attract new residents and more tourists; and Geelong to better adapt to closure of car manufacturing during the 2010s."

Illawarra Business Chamber Executive Director Adam Zarth has pushed for improved rail links to Sydney

"With 60,400 additional residents expected in the Illawarra over coming decades through new land releases alone, it is clear that this population is about to significantly increase and yet there are no proposals to bring commuters to Sydney any faster by rail," Mr Zarth said.