"I'd listen to the tooth fairy before I'd listen to Labor on how to build a road."

Roads and Maritime Services said the $16.8 billion budget for WestConnex included integration work such as that for a major intersection at St Peters in the inner west.

However,theupdated business case for WestConnex released in late 2015 states that upgrades to local streets at St Peters and Mascot are to be"funded outside of WestConnex",and were needed to"integrate WestConnex with the broader road network".

The latest document about the"integration work"for the 33-kilometre tollroad comes just two weeks after another document leaked from Transport for NSW estimated thecost of the "Sydney Gateway" project connecting WestConnex to Sydney Airport and Port Botany at as much as $1.8 billion.

The gateway project is named in the updated business case for WestConnex as part of stage two of the project.

Yet the government has insisted it is not part of WestConnex,and that the $16.8 billion for the toll road project included an"allocation"of $800 million for the motorway connection to the airport.

Thegateway connection of two lanes in each direction will have a separate toll to WestConnex,which means that motorists risk paying well above the toll cap of $8.60 in today's dollars if they want to drive from Parramatta to the airport.

The so-called escalation rate for WestConnex means its tolls will rise by up to 4 per cent a year.

An analysis by the City of Sydney Council in April put thecost of building and widening new and existing roads needed to support traffic flows from WestConnex at up to nearly $29 billion.

However,the state government disputed the council's calculations at the time,saying it had double counted the cost of some roads,while other add-on roads were needed to accommodate the growing city.