And it says that another section of WestConnex – a new M5 East tunnel from Beverly Hills to St Peters – will not alleviate traffic on the notoriously clogged existing M5 East motorway. A map showing which areas stand to win (green circles) and lose (red) according to the City of Sydney. "The M5 East will, despite the completion of the New M5, remain the preferred route connecting to airport, port and the city," says the study, by SGS Economics and Planning. The City of Sydney had previously commissioned SGS to study the economic case for WestConnex. This latest report models the traffic impact of the project. "The New M5 will not provide a more attractive route to these key destinations and will not relieve congestion on the M5 East. Traffic volumes on the M5 East will continue to increase by up to 25 per cent, leading to increased congestion and peak spreading," the study says.

The WestConnex Delivery Authority is poised to announce a number of major contracts for the WestConnex motorway, including a contract for a new M4 East tunnel from Homebush to Haberfield to duplicate Parramatta Road. When WestConnex was first proposed in 2012 one of the key justifications for the project was that it would remove traffic from Parramatta Road, helping to revitalise the much-maligned corridor. But SGS's study, along with the government's own later analysis, shows more cars will be attracted to Parramatta Road as they seek to avoid the tolls on WestConnex. "This growth in traffic along Parramatta Road will clearly jeopardise the government's planned urban renewal and population growth along this corridor," the report said. The study says the main benefits of the project, to be built in a series of stages over the next decade, would emerge when the last stage of a tunnel under the inner west is built.

But even so, the benefits will be relatively small compared to the size of the undertaking. A graphic from the study showing projected traffic in 2026. "Given the scale of the project the total changes brought about by WestConnex are modest," SGS's report says. "The improved road will benefit those that use it, but they do not represent a large share of all Sydney travellers," it says.

"Low growth in users means it is unlikely there will be sufficient demand to ensure the various WestConnex toll roads are viable." Cr Moore said: "The report confirms that investment in public transport, better use of the existing road network by alleviating bottlenecks, and introducing pricing mechanisms to reduce peak loads would be a more effective solution to traffic congestion." Cr Moore has been highlighting the potential impact of WestConnex on the mammoth housing developments around Green Square, and the report her council has commissioned shows that the motorway will worsen traffic in that area. A graphic from the study showing projected traffic in 2026.

But it also shows there would be relatively little impact on Newtown's King Street, another area of concern for anti-motorway protesters, because King Street is already at capacity. Cr Moore told the council that WestConnex "risks locking taxpayers into a financially risky tollway without due process, transparency and rigorous assessment of its business case". Council passed a motion, opposed by the two Liberal councillors and one independent, that called on the state government to halt the tender process for the new M5 and M4 East, and to publicly release information on the project's business case and traffic modelling. John Mant, a councillor on Cr Moore's team of independents, questioned whether any modelling would demonstrate WestConnex was a project worth doing. "The only people who don't know it's a dud are some old guys in the RMS ... and the people that own the tunnel boring machines," Cr Mant said.