Australia’s first driverless passenger train has completed its first test journey in Sydney in front of applauding politicians.

The metro train on Monday travelled 36 kilometres from the new Tallawong Station in the city’s northwest to Chatswood as part of a testing process before the Sydney Metro Northwest line opens to commuters within months.

The $8.3 billion railway line will have services running every four minutes during peak hour.

‘They said it would never happen … (but) today we see the train tested for the first time,’ NSW Premier Gladys Berejiklian told reporters on Monday.

The project has come in $500 million under budget, Transport Minister Andrew Constance said while standing alongside the premier.

‘The project is almost ready,’ Mr Constance said.

‘We’re finishing stations, car parks and testing trains to get the Northwest rail line open as quickly as possible.’

The Sydney Metro Northwest links the city’s northwest to Chatswood and includes a skytrain between Bella Vista and Rouse Hill.