An NRMA study has recommended work on the F6 extension start within three years.
The group commissioned the study Get Sutherland Shire Moving, a plan that aims to relieve congestion on roads in the area.
Any improvement to the road network in that area would also benefit Illawarra commuters driving to Sydney.
The study highlights a range of improvements, the biggest of which is the long-talked-about F6 extension, which it said should be given the "highest priority".
According to an NRMA spokeswoman, that means work should begin within three years.
The report, which forms part of the NRMA's efforts to lobby government for change, ranks the gains of building the extension as "high", stating "benefit is expected to be significantly above cost incurred".
The report noted that the Princes Highway, which begins where the F6 now ends at Waterfall, has to serve as a major arterial road, a suburban connector, a shopping strip and even residential frontage.
"A large proportion of the traffic on the Princes Highway is through traffic and would be better located on a freeway-standard road that connected the F6 with the rest of Sydney's motorway network to the north of the Georges River," the report said.
It also raises the possibility of linking the extension with the government's WestConnex road project to the west in the vicinity of Sydney airport.
Other recommendations in the report include improving the cycle of the traffic lights at the Acacia Road and President Avenue intersection, building a flyover for west-bound traffic at the Acacia Road-Princes Highway intersection and duplicating the right-hand turn bays on the highway at the Heathcote Road intersection.
NRMA director Michael Tynan said prioritising the extension to St Peters would have huge benefits to motorists in southern Sydney and the Illawarra.
"We know that the F6 extension will immediately reduce congestion in the Sutherland Shire and deliver real benefits to the local community through reduced travel times, reduced emissions and less wear and tear on vehicles," Mr Tynan said.
"We also know that commuters between the Illawarra and Sydney will have a much quicker and smoother ride once the F6 extension is built.
"It is an obvious solution to alleviate the choking congestion that is frustrating our members in southern Sydney and the NRMA will continue to be a fierce advocate for its construction," he said.