A survey of 850 NRMA members living near existing and potential sections of the M1 (F6) motorway found overwhelming support for it to be extended.
The motoring organisation said 74 per cent of 850 people surveyed in southern Sydney and the Illawarra were in favour of the project, which is now known as SouthConnex.
SouthConnex would shoot off WestConnex near Tempe and run through St George and Sutherland Shire to Waterfall along a route mapped out in 1951.
No indication has been given of how much tunnelling would be involved.
The NRMA said the survey result was a significant increase on the 66 per cent support found in a similar exercise in 2005
It called on the federal and NSW governments to ensure a business case, that is being worked on at present, "delivers value for money" and and that funding is provided in 2017 budgets for planning to get the project "shovel-ready".
The organisation said the corridor should be protected from further development, and community consultation should begin.
It said the survey targeted NRMA members living in Sutherland Shire, Wollongong, Mascot, St Peters, Tempe, Arncliffe, Rockdale, Sans Souci and Brighton-Le-Sands.
"The survey found 82 per cent of residents believed that local traffic congestion had worsened over the last 12 months," a spokesman said
"Almost half (47 per cent) said they spent up to 15 minutes longer in traffic a day, while over one-third (37 per cent) said their daily commute increased by up to half-an-hour.
The spokesman said 59 per cent of respondents had noticed an increase in heavy vehicles over the last 12 months.
Seventy-one per cent had changed their travel behaviour as a result of traffic congestion, with 69 per cent leaving home earlier and half getting home later.
The spokesman said 34 per cent of those surveyed had changed shopping or leisure activity locations locations to avoid traffic.
More than a quarter had said they did not go out as much.
NRMA director Marisa Mastroianni, who represents southern Sydney and the Illawarra, said residents in both areas would benefit extensively from the completion of the M1 Motorway to central Sydney.
“The results of this survey demonstrate yet again the strength of support in southern Sydney for SouthConnex and adds further weight to the NRMA’s call to get it built,” she said.
“For years, traffic congestion along major local roads like the Princes Highway, King Street and Taren Point Road has deteriorated and the number of heavy vehicles using local roads has increased, which has meant local residents continue to struggle with their daily commute.
“SouthConnex will ease local congestion by getting this traffic off our suburban streets and on a world-class motorway – where it belongs.
"The NRMA will continue its vital campaign to make this project a reality because we know what it means to our local members."
Sutherland Shire mayor Carmelo Pesce said in a statement the SouthConnex project represented a significant investment in the shire's road infrastructure.
Cr Pesce said the project would be welcomed by many shire residents, who had expressed concern regarding traffic congestion, particularly with the completion of many new developments.
