The WestConnex motorway and its off-shoots, particularly a planned third harbour road crossing from Rozelle to the northern suburbs called the Western Harbour Tunnel, are prompting transport authorities to examine ways to change tolls on existing major Sydney roads.

The development comes as the chief executive of the WestConnex Delivery Authority delivered a rousing defence of the $15 billion project on Friday, dismissing critics of the motorway as "privileged" inner-city residents, who wanted to impose their lifestyle on the rest of the city.

The re-evaluation of the city's motorway tolls is a logical development of the government's expansive toll-road program.

For instance the proposed Western Harbour Tunnel is intended to relieve pressure on the Harbour Bridge and Harbour Tunnel.

But motorists pay a toll only southbound on those two roads, whereas the trend for new motorways is to charge motorists in both directions.

This raises the possibility of significant traffic distortions unless tolls are unified. Some existing tolls could even be lowered to bring them in line with other roads.

Similarly, the third stage of WestConnex, which includes a tunnel between Rozelle and St Peters, is intended to relieve the existing Eastern Distributor and Southern Cross Drive.

But motorists pay a toll only northbound on the Eastern Distributor and there is no toll on Southern Cross Drive, which connects the Eastern Distributor to Sydney Airport.

A spokeswoman for Transport for NSW confirmed the government planned "to investigate a consistent distance-based tolling regime for the Sydney motorway network".

"This approach would be one way of helping to deliver high-quality roads and transport infrastructure," the spokeswoman said.

"The investigation will involve discussions with the community, private sector tollway operators and technical experts about options for consistent tolling on new and upgraded roads."

Any overhaul of tolls would not occur before the new roads were completed. The existing Sydney Harbour Tunnel reverts to government ownership in 2023, providing the opportunity to change the tolls.

Speaking to Fairfax Media at an industry lunch on Friday, Westconnex Delivery Authority chief executive Dennis Cliche confirmed the project would "focus the mind" of policy makers looking at the city's toll-road structure.

"It's obvious that people need to be thinking about it and I think people in government are always looking at it, it's their job," Mr Cliche said.

"I think there's a recognition that over time things have to be looked at, whether that results in a change tomorrow, next year, in 20 years," he said.

"If you were to reform it you would need to do it in a way that made sense, that was more equitable across the network."

But Mr Cliche's presentation to the Roads Australia lunch focused on the difficulty he was having in communicating the case for the project against what he described as a vocal minority.

"It is a very, I would say, inequitable debate that's being had," Mr Cliche said, after his presentation was briefly disrupted by protesters.

"The people who are making the most noise are those who already have the ability to jump in their car, drive wherever they want, they've got great public transport opportunities, they are a demographic that, generally speaking, is wealthier, and there is this attitude of 'I love my community don't mess it up'," Mr Cliche said.

"But they're not living in the mortgage belt. They don't have kids who are to some extent excluded socially from the opportunities that some people have," he said.

"It's not right for the people in an inner-city community to come in and enjoy their lifestyle and try and apply that to everybody else. And I think that's exactly what we are seeing."

The new Greens member for Newtown, Jenny Leong, who did not interrupt the lunch but appeared outside in support of the protesters, disagreed with Mr Cliche's characterisation and said there was "nothing minor" about community opposition to WestConnex.

"It's precisely because we want the whole community to be able to access public transport that we need  to stop billions of dollars being wasted on WestConnex," said Ms Leong, who claimed her inner-city seat with the assistance of anti-motorway campaigners.

The Transport for NSW spokeswoman said the government did not support congestion tolling.