The state's information watchdog has hit out at Transport for NSW for excessive secrecy over the $8.3 billion north-west rail link.

Transport for NSW has refused to release analysis it commissioned into the impact of terminating the north-west rail link at Chatswood, where thousands of commuters will have to change on to already crowded trains to the city.

Supporting the move: Transport Minister Gladys Berejiklian. Credit:James Alcock

Fairfax Media requested the analysis last year under the Government Information (Public Access) Act (GIPA), but was refused by Transport for NSW on four public interest grounds.

But in a review of that decision concluded last week, the state's Information and Privacy Commission said Transport for NSW had not shown how the release of the information could hurt the public interest.