The billions of dollars invested in Sydney's transport will increasingly be spent on mass transit systems over the coming decades rather than motorways, the head of the state's transport agency says.

Following a successful opening of a new metro rail line in Sydney's north-west, Transport for NSW secretary Rodd Staples said a "real shift in the thinking" about transport networks was under way.

"I certainly see the shift over the generations ahead that you will see in metropolitan Sydney more of the investment going into the mass transit than in the motorway network," he told the Transport Australia Conference.

Passengers on a driverless train on the Metro Northwest line between Rouse Hill and Chatswood. Credit:Peter Rae

"From the success we have seen on [Metro] Northwest, and the blueprint we have for the future, I think that balance will shift quite profoundly."