The WestConnex motorway is the wrong transport project for Sydney's future, a report commissioned by City of Sydney Council says.

The report argues the WestConnex motorway is unlikely to reduce traffic on local roads, exposes the taxpayer to huge financial risk, and will not benefit many western Sydney commuters.

Sydney Lord Mayor Clover Moore has emerged as a prominent critic of the WestConnex motorway, a series of projects that would together add to a continuous 33-kilometre motorway.

Last year the mayor requested that council commission a report into the impact of the motorway and that report, released on Monday night, produces multiple criticisms of the $11.5 billion project.

The report, by consultancy SGS Economics & Planning, argues it is "highly unlikely that there will be sufficient demand to ensure the various WestConnex toll roads are viable."

The WestConnex would make it easier for people from west and south-west Sydney to drive to the airport and the CBD, provided they were prepared to pay tolls.

But journey-to-work figures analysed by SGS show only about four per cent of workers in suburbs such as Penrith, St Marys and Camden travel to the CBD. Moreover, about 90 per cent of work trips to the CBD from the west are using public transport, compared with about 74 per cent for the city as a whole.

SGS's report also says WestConnex shares characteristics with other motorways that have financially failed, such as the Lane Cove Tunnel, Cross City Tunnel and Clem 7 in Brisbane, exposing the taxpayer to risk.

And it says WestConnex is not in line with current land use trends. The motorway was proposed before the federal government committed to build a second airport at Badgerys Creek, likely leading to more jobs growth in Sydney's south west.

The report also says there is little evidence WestConnex will calm surface traffic on local roads. The route of the M4 East component of WestConnex, for instance, no longer follows Parramatta Road, making it unlikely the motorway will trigger claimed urban renewal on the corridor.

Cr Moore said: "This report shows that WestConnex will not deliver for western Sydney, or for taxpayers, or the travelling public."

"Instead of 1950s projects like WestConnex, the government should be investing in public transport."

The prospect of the motorway has generated concern in the inner west where, on Monday night, the WestConnex Delivery Authority hosted an information session at Enmore Theatre.

The Baird government has prioritised the motorway, while the Labor opposition says it would build parts of the motorway but not others. Labor leader Luke Foley supports building new M4 East and M5 East tunnels to the north and south of the inner west, but will not commit to the location of the tunnel portals. Mr Foley also says the tunnels should not be joined – the third stage of the WestConnex project.

Principal of SGS Terry Rawnsley said a metro rail line along Parramatta Road between Westmead and Central would be a better fit for the city than a new motorway.

"It's the biggest transport project in Sydney's history and you want to be sure it is going to be an economically viable project. There's a lot of questions that someone needs to answer."

Mr Rawnsley said WestConnex could make it easier for people to drive between the western suburbs and the city, but there were other points to consider.

"The question is where will people park once they get to the CBD. You can get people from Penrith to the CBD quicker but if they are just circling the block looking for a park it's not much benefit."