Traffic congestion will worsen through many streets in the inner west as a result of the WestConnex project, says Leichhardt Council, whose mayor calls the analysis a "smoking gun".

The council is concerned that intersections along Parramatta Road will suffer when the motorway is built, and that traffic will build up on other streets or rat-runs through the inner city area.

An artist’s impression of the modified Concord Road intersection, looking east across the portal entry and exit ramps.

"Far from being the nirvana we've been promised by Roads Minister Duncan Gay, we now know that this $15 billion project will actually turn our part of Parramatta Road into a car park," said Leichhardt mayor Darcy Byrne.

For a report released on Tuesday, Leichhardt Council conducted an analysis of the Environmental Impact Statement for the M4 East component of WestConnex - a tunnel from Concord to Ashfield - and also attempted to quantify the impact of the motorway on roads not studied in the government's document.