The road from the Mountains out to Lithgow will be a sweeping four-lane highway with five new bridges, service roads and a major interchange at Jenolan Caves Road under plans released late last month by Transport for NSW.
The concept design and a Review of Environmental Factors (REF) show the 14-kilometre section from Little Hartley to Lithgow being upgraded to a divided road for its entire length.
New service roads will be installed for local traffic and two new rest areas created at Hartley Valley.
The REF said the three-year project, due to start in 2022, would - with other highway upgrades - save 10 minutes on the trip between Katoomba and Lithgow.
Some of the major work will occur around the intersection of Jenolan Caves Road, which is popular with tourists and also leads to Oberon. Twin bridges will be built in that area.
Extensive work will also be done around Coxs River Road at the bottom of Victoria Pass and a third westbound lane added for traffic climbing up River Lett hill.
The REF acknowledged that construction will have an impact on the natural environment. A biodiversity assessment identified nine threatened flora species with the potential to be found within the site as well as 17 threatened fauna species.
Targeted flora surveys are being undertaken this spring/summer to maximise the chance of detection of the species.
Records and habitat are also being checked to see what fauna may use the site. In addition, targeted surveys are being carried out for purple copper butterfly, the booroolong frog and breeding gang-gang cockatoos.
Biodiversity management measures will be implemented to reduce any impacts on threatened species, the REF said.
"Measures to avoid, minimise or offset potential environmental impacts have been considered throughout the options development process for the proposal. An important consideration has been to minimise potential impacts on biodiversity and particularly the removal of native vegetation."
TfNSW considered other routes, including around Newnes Plateau, but the Defence Department needs the land at Marangaroo. Other options would have involved an increased road length, steep grades and travel times.
The REF concluded: "The proposal would have some negative social impacts during the construction phase of the proposal, however, once operational, there would be long-term positive impacts on access and connectivity for local and regional communities, business, and industry."
Feedback is open until Tuesday, December 21 at https://caportal.com.au/tfnsw/great-western-highway/west.