Sydney's first driverless metro train line is expected to be opened to passengers on May 26, a week after the federal election.

Starting passenger services almost five years after construction started, the $7 billion Metro Northwest line from Rouse Hill to Chatswood will be the city's first privately operated suburban line, along which single-deck trains will run every four minutes.

Premier Gladys Berejiklian and Andrew Constance on a driverless metro train undergoing testing in March. Credit:Nick Moir

May 26 is understood to be the most likely date for the start of regular passenger services – to be operated by Hong Kong's MTR – partly because of time needed to inform commuters ahead of the resulting changes to rail and bus services in the city's north west.

The 36-kilometre line is the first stage of the Berejiklian government's plans for multiple metro train lines in Sydney. The second stage under construction comprises a line from Chatswood, under Sydney Harbour to the CBD and onto Sydenham and Bankstown, which is scheduled to be opened by 2024.