Transport for New South Wales has been ordered to hand over "highly confidential" 2018 train timetables to the ABC.

Key points: For almost three years, the ABC has been trying to get access to Sydney's future train timetables

For almost three years, the ABC has been trying to get access to Sydney's future train timetables It is expected they will reveal the impacts of the Sydney Metro on lines around the city

It is expected they will reveal the impacts of the Sydney Metro on lines around the city The NSW Civil and Administrative Tribunal has ordered Transport for NSW to release the timetables

The draft documents will detail how the state capital's thousands of train users will be affected by the construction of Sydney Metro.

The work is expected to have flow-on effects for commuters on several train lines, including express services from the Central Coast and those who use the Chatswood interchange.

The ABC first applied three years ago for access to the planning information about the 2018 standard working timetable, which is under development.

Buses will be needed to replace several routes when the standard gauge lines are ripped up for the new metro rail — with the work to begin in 2019.

During the case, Transport for NSW tried to persuade the NSW Civil and Administrative Tribunal (NCAT) that releasing a draft timetable drawn up in 2015 would not be in the public interest.

Labor's Jodi McKay said the Government is going to "extraordinary lengths" to block information that should be in the public domain. ( Supplied: NSW Parliament )

Transport for NSW has been contacted by the ABC, but has yet to decide whether to appeal against the decision.

A second ABC application for access to more recent timetable information is yet to be decided by the Tribunal.

Labor's Transport Spokeswoman Jodi McKay said the Government spent too long trying to keep the timetables confidential.

"What we're seeing more and more [is the] extraordinary lengths that this Government is going to, to block that information being released," she said.

"This is information that should be in the public domain, it's information that people are entitled to and I think it's a very dangerous precedent."

NCAT rejects timetables argument

In evidence to the tribunal, Transport for NSW's principal manager for rail service planning, Nikolai Prince, said a 2013 leak of the previous standard timetable had interfered with the department's work.

He said there were 1,500 complaints and resources were diverted to respond to the Transport Minister's Office and the media.

Mr Prince added the leak raised an expectation that the timetable could be changed, when it had been "effectively locked down".

It was argued a similar situation could develop if the material requested by the ABC about the 2018 timetable was released.

He also said the material had been superseded and if released could be misunderstood or misinterpreted, resulting in industrial action and possibly delaying major infrastructure projects.

The construction of Sydney Metro is expected to affect several lines in the city's train network. ( ABC News: Amanda Hoh )

Michael McKinnon, the ABC's freedom of information editor, submitted to NCAT that: "If the material was historical, it would be difficult to understand how it would generate a large number of complaints."

Ultimately, the senior member hearing the case, Suzanne Leal, rejected each of Transport for NSW's arguments against disclosure.

In a judgment yesterday, she said: "I accept that the release of the material may be misinterpreted or misunderstood by the public but this is not something I can take into account in my determination.

"On this evidence before me, I am not satisfied that there is an overriding public interest against disclosure of the requested material."