Direct train services from Penrith could be cut back as the city's $20-billion Metro project wavers on its promise of a faster, better rail system for all.

Documents obtained by the ABC reveal the NSW Government has considered plans to bring new express trains to the Northern line, while reducing peak-hour services from Penrith, Kingswood and Werrington.

There are also hints that Sydney's suburban trains may become more crowded.

An impact document predicts a reduction of 'West to North' capacity by 25 per cent, suggesting more passengers on already crowded trains from Sydney's western suburbs.

The planning documents were secured after a successful three-year legal battle with Transport for New South Wales, with two appeals to release the information under the GIPA Act.

Commuters at Penrith train station could have their peak-hour services reduced. ( AAP: Dean Lewis )

Last year Transport Minister Andrew Constance said the $20-billion Metro project would deliver a "massive boost" to the entire train network.

"It will also mean faster and more frequent services will be able to be delivered on the Sydney Trains network from other major centres like Penrith and Blacktown," he said.

The comments echoed those of former premier Mike Baird who said: "Whether it is busting congestion or providing brand new Metro train lines to reduce crowding on our public transport, these projects will make a huge difference to people's lives."

The timetable changes revealed today assist the operation of the privately run Metro line, which will take over a reconfigured Epping-to-Chatswood line.

However, they will have a complex domino effect on the city's railways as existing services are rerouted, or even cancelled.

Penrith loses, Rhodes wins

Penrith currently enjoys 11 fast trains to the city during the 7:00am-to-8:00am peak-hour period, but a 2018 concept map suggests the western population centre could lose four services with capacity for up to 4,000 passengers.

From 2018 on, Penrith's peak-hour travellers may lose direct access to Town Hall, Wynyard and the North Shore, with train services instead terminating at Central.

Passengers would need to change trains to continue into the city and north, something that could increase journey times and station congestion.

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While the western suburbs are set to lose services, the concept timetables show the Northern line will be boosted.

Starting next year, passengers from Normanhurst, Thornleigh, Pennant Hills and Beecroft are re-routed away from a closed Epping-to-Chatswood line.

Two new peak-hour services are also accommodated in the concept timetables.

During peak-hour, five fast trains will depart Epping and service just five stops — Eastwood, West Ryde, Rhodes, Strathfield and Central — supporting high-rise population centres.

Penrith's peak-hour services will terminate at Central under the new plan. ( ABC News: Amanda Hoh )

Central Coast loses services, longer journeys across West

Planning documents suggest Central Coast commuters may also face a shock in 2019 with the end of direct services from Wyong and Gosford to the North Shore line.

Instead of express peak-hour services via Chatswood to the city, it appears Central Coast trains could also be re-routed down the Northern line via Strathfield, with most services commencing from Gosford.

The re-timetabling of peak-hour trains and slower stopping patterns down the Northern, Southern, Inner-West and Western lines is another impact of the Sydney Metro.

For instance, travellers from Liverpool can expect to take up to 10 minutes extra to the CBD.

A rail planning map reinforces this and shows two extra Northern line trains travelling between Strathfield and Central during the morning peak, to as many as 15 per hour in 2019.

Loss of Penrith services to help with demand on Northern line

The ABC contacted Railcorp former general manager and head of timetabling Dr Dick Day, who examined the concept timetables.

He suggested the motivation behind Penrith's modelled loss of services could be to help the Northern Line cope with additional demand, created by re-routed trains.

"A likely reason for terminating Penrith trains at Central is to create additional track space into the City via Strathfield," Dr Day said.

Sydney's train system will be affected by the introduction of the Metro. ( AAP: John Donegan )

Railway consultant Sandy Thomas, who also analysed the Government's documents, said he feared much needed extra capacity would not be delivered in the proposed changes.

"On some lines there are actually proposals for fewer peak hour services from Penrith to St Marys, Epping to the CBD, from Berowra to Hornsby, and from Hornsby to Lindfield," he said.

He says the documents suggest major infrastructure upgrades to signals and tracks are needed if the suggested timetable changes are to run successfully.

"It appears these improvements at Rhodes and elsewhere on the main North line are subject to the completion of extra tracks between Rhodes and North Strathfield.

Both rail experts expected significant alterations would be made to the timetables received by the ABC.

Planner says nothing final but timetable expert disagrees

In an NCAT hearing, senior planner Nikolai Prince said the documents, while conceptual, did represent timetable solutions under development by Transport for NSW. He also suggested impacts on customers were already considered by planners, negating the need for wider consultation.

Transport for NSW was unable to answer specific questions about the proposed changes yesterday, but in a statement it said that future timetables had not been finalised, and it would clarify changes as they were locked in.

"Transport for NSW will not confuse its customers by ruling in and out possibilities for a timetable that is still being worked through," the statement said.

"Options for all lines remain unconfirmed, unless already announced by the NSW Government."

Sorry, this audio has expired Draft timetables reveal proposal to slash peak-hour train services in Western Sydney

In a radio interview on ABC Sydney this morning Transport Minister Andrew Constance criticised the ABC for confusing commuters with a story based on old planning documents.

However, the documents were obtained less than two weeks ago after a ruling by the NCAT found in the ABC's favour for release under public interest considerations.

Timetable expert Dr Day lamented the fact Transport for NSW had failed to release more up-to-date information – as requested by the ABC.

"Actual work on a 2018 timetable would now be highly advanced with hardly any time to alter and produce all the required documentation, before we are faced with the Epping-Chatswood closure.

"So why do they refuse to make real information available?"

He suggested involving passengers in additional consultation before decision making was finalised would be beneficial to timetable outcomes.

A decision by Transport for NSW to block the release of additional documents is currently under appeal by the ABC.

You can read the full concept timetables released to the ABC here.