The NRMA has thrown its support behind the efforts of a number of South Coast and southern Sydney Liberal MPs to get the F6 extension "shovel ready" in two years.
Last week Kiama MP Gareth Ward announced that he and six other Liberal MPs were petitioning the government to get working on the F6 extension from Waterfall to St Peters.
NRMA Deputy President Michael Tynan said the motoring group had long been lobbying for the extension and would work with the MPs on this issue.
"Sydney is getting WestConnex and NorthConnex, which is great, but we shouldn't forget what we're already calling SouthConnex - the M1 Princes Motorway extension," Mr Tynan said.
"We have lobbied for planning money for some time now, along with hosting workshops attended by industry stakeholders, MPs and local councils.
"These meetings helped put the M1 Princes Motorway extension back on the map and in the minds of decision makers."
He said the need for the extension had only increased since it was first talked about in the 1940s.
"The fact that the corridor for the missing link has featured on street directory maps for more than half a century tells us there was a need for the motorway then," he said.
"Fifty years on, local motorists need it more than ever to take pressure off the Princes Highway and The Grand Parade.
"Local road users deserve this link that would cut travel times and take trucks off local roads."