All rail lines would operate independently. The Airport Line would terminate at Central. And billions would need to be spent on new bridges and tunnels to offer more reliable trains for western Sydney.

Bureaucrats and consultants have developed these proposals and others for Transport for NSW as part of an implementation plan for the government's "Sydney's Rail Future" strategy.

The plans have not been made public. And there is a good chance the state government will opt for cheaper and less drastic policies to expand the capacity of Sydney's train system.

But investigations by Fairfax Media can reveal at least a partial picture of the planning that lies beneath glossy government brochures on the future of Sydney public transport.

The thrust of the plan, adopted by senior executives in Transport for NSW in mid-2013, is for each of Sydney's rail lines to operate separately.

This is so trains don't need to merge tracks, which limits how many can run on a line. It also increases the chance that problems on one train line will cause delays on another.

But the proposals would be hugely controversial. There would be a vast cost to many of the elements, far exceeding what the government has so far promised for upgrades to the existing network.

And they would be unpopular with many commuters, who would be forced to change trains where they didn't before.

The plans include running trains on the existing airport line in a shuttle between Revesby and Central.

Dedicated trains would run on the line, with space for luggage. But the shuttle would draw critics because all passengers wanting to travel between the city and the airport by train would need to change at Central.

To get around this, the plans seen by Fairfax Media envisage building a new platform at Central to allow commuters disembarking from Airport Line trains direct access to the new rail line the Baird government wants to build through the city, scheduled to be finished by 2024.

The benefit of terminating Airport Line trains at Central is that it would create more space for other services to run around the City Circle. The government has already said it would remove Bankstown Line trains from the City Circle, which would create more room for trains from the Inner West and Campbelltown and East Hills to run around the inner circle.

But many of the biggest works in the plans involve major engineering projects on the Western Line, Sydney's busiest rail corridor.

Last month Fairfax Media revealed the government's own dire predictions for the Western Line, including the expectation that trains would regularly be too full to board from further west than Parramatta.

The unpublished plans seen by Fairfax Media offer an array of costly engineering solutions to run more trains on the Western Line, with a bill of more than 7.5 billion. By contrast, both the government and the opposition have promised about $1 billion in funding for upgrades to the Western Line.

The unfunded projects, which were included in the unpublished implementation plan for Sydney's Rail Future, include a tunnel for new tracks between Croydon and Granville and a $600-million flyover or bridge to help separate Northern Line trains at Strathfield.

Another project is to buy new high-capacity trains for the Western Line, with a new electronic signalling system.

 

And another listed on the internal government documents but not announced or funded is $700 million in new tracks on the lower northern line between Epping and Strathfield. A spokesman for Transport for NSW said "extensive investigation" had shown that these tracks were not needed. "There is ample capacity - it has never been a confirmed project," he wrote in an email.

Under the plan drawn up in mid-2013, these projects were to have started this year so they would be ready in time for the opening of the North West Rail Link in 2019.

The North West Rail Link will put a strain on some parts of the existing rail system, requiring passengers disembarking at Chatswood to board North Shore line trains to the city. The project will also make it more difficult to run express services from the Central Coast down the existing North Shore or Northern Lines.

But work on the projects listed in the unpublished plans have since been stalled, and Transport for NSW has started a new process of developing a timetable for the opening of the North West Rail Link in 2019 that would use existing rail infrastructure.

Transport Minister Gladys Berejiklian and Transport for NSW did not deny the plans, but said they were not government policy.

One of the implications of the proposals seen by Fairfax Media is that they would, in theory, make it easier for individual rail lines to be privatised, but it is understood this was not the motivation for developing the plans.

Asked this week about the potential for more lines to be privatised, Ms Berejiklian said: "We've always said that the North West Rail Line will be operated by the private sector and that line will obviously go all the way down to Bankstown eventually. And that's been in our plans and there's no further plans beyond that."

Separately, the minister also said the Sydney's Rail Future document would stand the test of time.

"That we now have a dedicated team focused wholly on future service and infrastructure requirements, from the opening of the North West Rail Link right through to the opening of Sydney Rapid Transit, shows how serious we are about getting it right."

But the plans seen by Fairfax Media focus on a number of issues that will eventually need to be confronted.

Take what is planned for the Bankstown Line. Under the government's announced plan, the existing line as far as Bankstown Station will run automated single-deck trains connecting to the North West Rail Link through another harbour crossing.

But the Bankstown Line runs further than Bankstown to the west - in two directions to Lidcombe and Liverpool via Cabramatta.

The plans seen by Fairfax Media include running shuttle services, either as light or heavy rail, on the existing lines between Bankstown, Lidcombe and Cabramatta.

This would mean that anyone travelling from the station on these lines, such as Berala, Chester Hill or Villawood, who currently gets a direct train to the city would need to change trains at least once.

Neither Ms Berejiklian nor Transport for NSW have ever explained what will happen to stations west of Bankstown once the line east of Bankstown starts running automated services when the new harbour crossing is built in about 2024.

A spokesman for Transport for NSW said: "Transport for NSW is considering a number of options for customers between Bankstown and Lidcombe and Cabramatta after the introduction of Sydney Rapid Transit, including a higher frequency of train services."

The plans seen by Fairfax Media also include running light rail services between Parramatta and Epping, a corridor long earmarked for a heavy rail route. The idea included taking over the existing Carlingford train line.

A spokesman for Transport for NSW said: "Transport for NSW is considering a number of options - this will in part be informed by investigation work now under way as part of the Western Sydney light rail project."

The vision of Sydney's rail future devised in mid-2013 - it involved work by numerous engineering and financial consultants such as Evans and Peck - may never eventuate.

Many of the proposals have since been internally discredited, such as the idea of running light rail between Bankstown, Lidcombe and Campbelltown. Those tracks also need to be used for freight trains, which cannot run on the same tracks as trams.

But whatever happens, and whoever is in power from April, someone will have to work out what happens to trains that run west of Bankstown.