As the NSW Government prepares to start early work on the Medlow Bath section of the upgrade later this year, it is also getting ready to announce the successful tenderer for the duplication of the highway from Katoomba to Blackheath and from Little Hartley to Lithgow.

Those parts of the upgrade, known as the east and west sections, have the required state and Commonwealth funding, whereas the middle section, a proposed tunnel from Little Hartley to Blackheath, still needs Commonwealth funding.

Transport for NSW said on Tuesday traffic conditions will change on the Great Western Highway between Katoomba and Blackheath from this Monday, August 15 for what are described as "further geotechnical investigations along the corridor".

"Work will include use of a geotechnical drilling rig and minor digging work with a small excavator, with the investigations to inform the design of a highway upgrade between Katoomba and Blackheath," a release from Transport for NSW said.

The work hours will be 7am to 6pm from Monday to Friday and 8am-1pm on Saturday, weather permitting, and the work is expected to be completed by Saturday, October 29 - again, weather permitting.

Traffic changes, including a reduced 40 kilometre an hour speed limit and temporary lane closures, will be in place where necessary, according to Transport for NSW.

It also says pedestrian access may be temporarily disrupted and detours will be in place along existing roads and pedestrian trails.

The work between Katoomba and Blackheath will continue a period of disruption in the Blue Mountains, which has included changed traffic conditions at Mount Tomah and Kurrajong Heights on Bells Line of Road for routine maintenance, the closure of a section of the eastbound lane of Bells Line near Berambing for geotechnical investigations and the closure and recent reopening of the rail line between Blackheath and Mount Victoria.

As well, there will be changes this week at Scenic Hill on Chifley Road.