Traffic projections near the WestConnex Along King Street, the RMS figures show a continual increase in cars travelling in the morning and afternoon peak hours between the years 2011, 2026 and 2036. There is a similar story for other major roads around the inner south of Sydney, including the already densely congested Botany Road, O'Riordan Street, Cleveland Street and Southern Cross Drive. The modelling challenges claims that construction of the motorway will quieten local roads. At best, it seems, the motorway might prevent local roads becoming busier than they would be if it were not built. Prior to the March election, Mr Gay said that, without the third stage of WestConnex, 120,000 cars per day would be "spewed into Newtown, Balmain, Leichhardt, Erskineville".

But, he said, this scenario would be avoided because "we will have a magic tunnel that will go underneath and King Street will become the nirvana that we always hoped it would be and we always thought it would be and I might even try and buy a black shirt." Last week, Mr Gay told a business lunch that once completed "WestConnex will remove large volumes of through traffic off inner-city residential streets." "Instead of rat runs through suburban streets, motorists can jump on and off this motorway," he said. In a response for this story, a spokeswoman for the WestConnex Delivery Authority said: "In 20 years, an extra 1.6 million people will be living in Sydney. More people will mean more trips on our roads." "WDA traffic modelling, which has been ticked off by independent infrastructure experts, shows the inner south will improve with WestConnex as opposed to a do nothing scenario," the spokeswoman said.

The figures obtained by Fairfax Media were created within RMS using the department's strategic traffic forecasting model. The documents include information about when the model created the traffic forecasts. The forecasts do not align with the traffic forecasts released by the WDA for the first stage of the project, a widened M4 motorway. The WDA uses traffic forecasts for 2021 and 2031, as opposed to the figures for 2026 and 2036 obtained by Fairfax Media. A professor at the Institute of Transport & Logistics Studies, University of Sydney, Michiel Bliemer, said in the short term a new motorway could remove traffic from local roads. "But quite quickly it will have the phenomenon of induced demand, which is that all the other roads around will become less congested and more attractive to drive on," he said, which would probably attract public transport users back to their cars. "It usually helps temporarily but because of induced demand and population growth, traffic volumes would go up again," Professor Bliemer said.

Fairfax Media asked Mr Gay's office and the WDA why, if detailed traffic modelling was available for WestConnex and the roads around it, it had not been released to the public. The WDA spokeswoman said: "Interpreting background data can be misleading." "As per standard processes, environmental impact statements are being produced and include full details of traffic modelling for each stage of WestConnex," she said. After an embarrasing interview with Seven News, in which he was unable to answer basic questions about the motorway, Mr Gay said in March that 120,000 cars per day would use the third stage of WestConnex.