The report by Professor Andrew McNaughton - which looked at four possible faster rail routes (including a "southern coastal route") - has been in government hands for a year.

Last March, Regional Transport Minister Paul Toole told a budget estimates hearing that he had received it.

In November, Transport Minister Andrew Constance said it would be released.

But a year after its completion, what is inside that report is still a secret.

Such a secret in fact that not even a freedom of information request to Transport for NSW can shake it loose.

Wollongong MP Paul Scully lodged a GIPA request for the report, but was refused because it was "cabinet information", but he claimed it had never been to cabinet.

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"You can't help but be sceptical when the government trumpets this as a major report into the future of our transport network, particularly on the South Coast and then sits on it, hides it and doesn't even suggest that it's going to be released at any point in the future," Mr Scully said.

"One wonders what the report actually says but also if there are any other things in there that are immediate concerns about the current South Coast line.

"I fear it's yet another report that holds out hope to commuters but will end up doing nothing more than gathering dust on a shelf."

When asked, a Transport for NSW spokesman would not comment on whether the report would ever be released.

"Transport for NSW is taking the time to get this right," the spokesman said.

"The NSW government will update the community as soon as it has more to say."