Nineteen community groups in Blackheath have banded together to support a long tunnel underneath the town.
The groups have put their names to a flyer which will be letter-boxed to all residents over the weekend.
It points out that a short tunnel would threaten 12 homes and potentially destroy Sutton Park, a much-used rest area.
It would also have a negative impact on surrounding properties.
The long tunnel, with a portal south of Evans Lookout Road, would be a true bypass of the town, the flyer said.
The decision to remove three above-ground options through the town was announced by the regional transport and roads minister, Paul Toole, last month.
It was greeted warmly by those who lobbied against proposals to duplicate the highway along Station Street, over the scenic Centennial Glen or through the middle of town.
The flyer congratulates those involved: "Well done to everyone in our community who worked very hard and succeeded in getting these options off the table. This was a great community effort."
But it continues that "the fight is not over" and encourages residents to say no to the short tunnel option.
The signatories to the flyer include the Blackheath Alliance, CWA, Rotary, St Vincent de Paul, Streetscape, the Rhododendron Gardens and the Rhodo Festival committee, RSL, Neighbourhood Centre, Vipassana Meditation Group and Medlow Bath Residents Association, as well as the two residents groups which were formed to fight the previous options, Save Centennial Glen and Save Station Street.
Meanwhile, Transport for NSW has announced the deadline for submissions on the tunnel has been extended by two weeks to November 28.
It also revealed it has already received more than 500 submissions on the tunnel options.
And more than 4,000 people have visited the project's virtual consultation room to learn about the proposed upgrade at Great Western Highway/virtual.
TfNSW acting director west, Alistair Lunn, said the extension would help ensure the community had time to review the options in more detail.
During the consultation period, residents are able to speak to a TfNSW team member on 1800 953 777.
