Gladys Berejiklian says she will be happy to investigate a system where train users parking at commuter car parks use an Opal Card or similar system to show they will actually catch the train.

The Transport Minister, who on Friday announced a $150 million expansion for commuter car parks in western Sydney and the north west, said commuters who parked near train stations should be able to park for free.

Gladys Berejiklian with Parramatta MP Geoff Lee (left) and Premier Mike Baird at Parramatta Station this week. Credit:Daniel Munoz

But she has raised the possibility of using technology to restrict those car parks to people who use public transport.

"We haven't done any formal investigations in that regard yet, but it is something I would be happy to look at," Ms Berejiklian said in response to questions from Fairfax Media.