Sydney's $16.8 billion WestConnex project will be audited for a second time due, the NSW Auditor-General has confirmed.
Opposition transport spokeswoman Jodi McKay has welcomed the audit saying "there needs to be transparency in this botched project".
The first audit was carried out in 2014 and the second will be conducted within the next two years, NSW Audit Office executive manager Barry Underwood told AAP on Friday.
"It's worth a revisit," Mr Underwood said.
Auditor-General Margaret Crawford has decided to look at it again because of its size, cost, risks and the level of public interest.
The audit will coincide with the next NSW state election in 2019 which may cause headaches for the Berejiklian government.
The controversial toll road has caused disruptions during construction and required the compulsory acquisition of properties.
Its cost was revised to $16.8 billion in late 2015 - some $6.8 billion more than first estimated.
Since then, it's been subject to a series of leaks about potential further cost blowouts, which have been damaging for the coalition government.
A fresh audit was "timely and appropriate given the project has blown out by $7 billion", Ms McKay told AAP.
The Labor MP hopes the audit will look at the role of the Sydney Motorway Corporation in the financing and construction of the project.
The government announced in August it would sell a majority stake in the corporation to fund the future development of WestConnex.
Earlier this year, a Commonwealth auditor-general's report into WestConnex found major flaws in the way $3.5 billion in federal funding was being committed to the project.