The Andrews government is trying to keep Victorians in the dark on doubts over the proposed West Gate Tunnel, relying in part on a precedent of confidentiality set by former premier Denis Napthine during his failed bid for the East West Link.

The premise is being used to deny the government's own hand-picked experts access to a review of traffic predictions for the $5.5 billion toll road.

An artist's impression of the West Gate Tunnel exit near Shepherd Bridge in Footscray.

The report by New Zealand transport expert John Allard is critical of traffic modelling done by project builder Transurban and the government.

That modelling helped Premier Daniel Andrews justify his support for the toll road, and to claim it would return $1.30 to the Victorian economy for every $1 spent building it.