New South Wales Transport Minister Gladys Berejiklian would not confirm the length of time the Epping to Chatswood line would need to be shut down, but it is understood the government is preparing to reveal how it intends to transport the tens of thousands of commuters who currently use the line.

Fairfax Media has previously reported industry speculation the line would need to be shut for between three months and six months to allow for a new signalling system and screen doors – features of the fully automated north-west rail link – to be installed.

The Epping to Chatswood line, which opened only in 2009, will be handed over to the new operator of the north-west rail link. When that line opens in early 2019, trains will run in a shuttle between Rouse Hill and Chatswood.

To allow for the line to be opened in early 2019, it is likely the Epping to Chatswood line, which includes stations at Macquarie University and Macquarie Park, will need to be shut early that year, or in late 2018.

Asked how long the line would be closed, Ms Berejiklian said: "We have just signed the contract and I look forward to updating the community soon about details relating to the conversion.

"Customers will be able to catch more trains between Epping and Chatswood – the number of train services will increase to 15 trains an hour in the peak, almost four times as many as today."

Premier Mike Baird joined Ms Berejiklian at a ceremony in Castle Hill on Tuesday to announce the signing of the contract to operate and supply the trains on the north-west rail link.

The project will be Sydney's first privately operated heavy rail line for commuters, the state's largest ever public private partnership, and the first fully automated rail service in the country.

Ms Berejiklian said trains would run every four minutes on the new line in peak hours, and the operator of the line would be required to run 98 per cent of trains on time.

"As far as public transport is concerned, it doesn't get much bigger or better than this," she said.

Ms Berejiklian also said three major contracts – a tunnelling contract, a viaduct contract and a contract to fit out the stations and operate the line – had been signed, and the multibillion-dollar project was expected to come in under budget.

"I can confirm that the project will come in at less than the [estimated] $8.3 billion," Ms Berejiklian said.

The trains will be single-deck, and models displayed at the Castle Hill information office show a combination of seats on the side of the carriages and in rows.

Ms Berejiklian said there would be between 5500 to 6000 seats an hour in each direction, out of a total capacity of 17,280 passengers an hour in each direction.

This is less than the seating ratio of Sydney's double-deck trains, which carry about three-quarters of their passengers seated when full. But Ms Berejiklian highlighted the advantages of the frequency of the service.

"I can assure you that if you want a seat, there will be one," she said.

The North-west Rapid Transit consortium includes MTR Corporation (the operator of Hong Kong's trains), John Holland, Leighton Contracts, UGL Rail Services and Plenary Group. The trains will be supplied by French conglomerate Alstom, and will be fully imported from overseas – another first.

The state government's long-term plan is to extend the north-west rail link over Sydney Harbour and connect it with the Bankstown line.