THE north-west rail link will require another $4 billion of investment in the rest of Sydney's rail network beyond what the government has budgeted for, internal Transport for NSW documents say.
The extra infrastructure comes on top of the estimated $9 billion to build the north-west rail link, planned to run as a shuttle between Rouse Hill and Chatswood in northern Sydney.
The Transport Minister, Gladys Berejiklian, disputed the need for extra works yesterday.
But internal Transport for NSW documents, obtained by the Herald, show changes to other stations and lines will be triggered, even though the link is being planned as a largely separate line to be run by a different private operator.
The biggest predicted expense will be about $1 billion for 25 to 30 new double-deck trains.
The north-west rail link will be built for single-deck trains.
But extra double-deck trains will be needed to take people who get off the north-west rail link at Chatswood to continue to the city on the North Shore Line.
If the government did not buy new trains, it would mean retaining older non-airconditioned trains for longer.
The Herald revealed yesterday analysis by consultants at Arup for the transport projects division of Transport for NSW that showed almost one in two passengers getting off the north-west rail link at Chatswood would be unable to board the first connecting train to the city because of overcrowding.
In addition, the analysis said platforms one and two at Chatswood could become so crowded that commuters would struggle to get off some north-west rail link services.
Ms Berejiklian dismissed the concerns, saying they were based on incomplete information. ''That data … was essentially very preliminary data, from what I understand,'' she said.
''It didn't take into consideration that we will be increasing the number of services from the north shore to the city to 24 an hour,'' she said. ''Currently we are getting about 17 or 18 across, so that will increase substantially by the time the rail line is open.''
But she has not explained how she would fit another seven trains an hour down the North Shore Line in the morning, beyond talking about a simplified timetable and technology upgrades.
According to analysis obtained by the Herald, the $4 billion in extra infrastructure would not solve predicted congestion problems at Chatswood but would give the government the best chance of managing them.
To free space on the North Shore Line, all trains from the central coast would be redirected to the city on the Northern Line through Epping and Strathfield, instead of Chatswood.
But this would mean extra track would be required on the Northern Line between West Ryde and Rhodes.
To run more trains down the North Shore Line another platform would be needed at Hornsby, as well as space to turn trains around.
And Transport for NSW has also drawn up plans for extra tracks to St Leonards.
These would be needed, in any event, if the government did start building a second rail crossing of Sydney Harbour.
Ms Berejiklian said Transport for NSW had advised her the extra projects were not needed for the success of the north-west rail link.