The New South Wales Information and Privacy Commission says Transport for NSW has been too secretive about the massive $8.3 billion north-west rail link.

In its finding over an investigation by Fairfax Media last year, the Information and Privacy Commission has said Transport for NSW did not explain what harm could come to the public interest when it withheld the analysis justifying the large-scale project.

Media outlets requested a copy of the analysis under the Government Information (Public Access) Act (GIPA) in 2012, but were refused by the state’s transport body on four public interest grounds.

Transport for NSW commissioned the report to look into the potential impact of terminating the north-west rail link at Chatswood, at which point thousands of commuters would be forced to squeeze into already crowded trains for the rest of their journey.

“We are not satisfied that Transport's decision to withhold the information was justified," a senior investigator, Kathryn Luis, said in a written statement.

The Fairfax outlet reportedly obtained the documents independently, and said they show more than 40 per cent of commuters from the north-west rail link would not be able to get on the first Chatswood train to the city - as it would already be too crowded.

The report also allegedly claims 15 per cent of commuters would not be able to fit on ether of the next two trains.

In addition, if a single service to the city was delayed, thousands of commuters would have to wait for up to six trains to pass before there would be enough room to actually get on.

The review has led to more reviews as the Information Commission cannot order departments to release information – it can only recommend that it review its decisions. As such, Transport for NSW is conducting an internal review into its decision not to release the 116 documents covered in the original request for information.

Some transparency would save media groups from having to poke around for scraps of information, though details from official channels have not elucidated much.

Transport Minister Gladys Berejiklian has dismissed the report which said many may be waiting for several trains to pass each day, she claims the analysis was preliminary and based on untested assumptions. Ms Berejiklian had previously said that when the link is built the line will have twenty-four trains running on it, rather than eighteen currently, but a later departmental statement indicated it would only be bumped up to twenty.

“The interchange at Chatswood is an interim measure while the NSW government gets on with the job of building a second harbour crossing, a new CBD rail line and new CBD railway stations,” a Transport for NSW spokesperson said.