The largest transport project in the country could be shielded from public scrutiny after the government transferred control of the $15.4 billion WestConnex motorway to a "private corporation".

The transfer means information about the Sydney Motorway Corporation, which is now in charge of building the motorway, cannot be captured by freedom of information requests.

The government this month closed the former WestConnex Delivery Authority, and transferred its functions to the Sydney Motorway Corporation, once the organisation solely responsible for financing the road.

One implication of the transfer is that there are now no representatives from transport agencies on the board of the organisation responsible for building the 33-kilometre WestConnex - instead, the board is made up of treasury officials, builders and financiers.