The first stage of WestConnex includes widening the M4 from three to four lanes in each direction between Parramatta and Homebush.
Next comes an extension of the motorway - the M4 East - via a six-kilometre tunnel of three lanes in each direction from west of Concord Road, North Strathfield to Parramatta Road and the City-West Link at Haberfield.
The planning application for the M4 East has now been lodged and all stage-one plans are open for community consultation. Mr Gay said the changes would transform Parramatta Road and cut travel times across the length of the planned roads.
"(Parramatta Road) is chaos, it's practically at a standstill," he told Macquarie Radio.
"We're removing those trucks and cars and putting them underground ... We want to mitigate the amount of houses we remove but the end product is going to be a better community for the people that live there."
Greens NSW Roads spokeswoman Mehreen Faruqi said residents in the inner west suburbs of North Strathfield, Ashfield, Concord and Haberfield would not only lose homes to WestConnex but face increased pollution and congestion.
"The billions going into Westconnex to build tunnels and acquire homes is billions not going into improving public transport to reduce congestion, make commutes faster and reduce pollution," Dr Faruqi said.
The Greens want light rail along Parramatta Road.
But Mr Gay scoffed at that suggestion.
"Spare me," he told Macquarie Radio.
"Seven years to construct the thing, where are the trucks going to go in the interim and how are you going to carry your fridge back from Bunnings on light rail?"