The only independent review of the business case for the $14 billion WestConnex motorway, the biggest transport initiative in Australia, concluded "it was not able to form a view on whether the project is a worthwhile and prudent investment … for the NSW government".

This detail emerges in a scathing report into the governance of the motorway, the signature road-building project of the Baird and Abbott governments, released on Thursday by the NSW Auditor-General.

The revised path of the WestConnex.

Auditor-General Grant Hehir's report highlights the lack of independent monitoring of the concept, business case and tendering for WestConnex, a series of projects that would form a 33 kilometre toll road though inner-Sydney.

The NSW Roads Minister, Duncan Gay, immediately rejected the criticism. Mr Gay said: "We respectfully disagree, we have followed world best practice on procurement and delivery and it complied with the processes set by cabinet."