And Mr Toole says a tunnel under Mount Victoria is "locked in", along with a tunnel under Blackheath, as part of the duplication.

Hours were added to the trip between Sydney and Bathurst when the Easter long weekend collided with the closure of part of Bells Line of Road due to landslides caused by heavy rain in March.

Bells Line has since reopened in a limited capacity, but transport from Orange and other areas of the Central West to the state capital remains a hot topic.

The NSW Government has committed $2.5 billion so far to a duplication of the highway from Katoomba to Lithgow and Mr Toole said work is continuing to get ready for the mammoth project.

"There's been a lot of drilling going on in the [Blue] Mountains," he said.

"Anyone who's travelled on the Great Western Highway would have seen that there are large drilling machines that have been drilling into the earth.

"We're having a look at where those portals might be for the establishment of tunnels - where they're going to go in, where they're going to come out.

"We're working with communities - there has been a lot of consultation. Environmental studies have been undertaken.

"So there's a lot of work that's happened already."

Mr Toole said a four-kilometre tunnel will run under Mount Victoria as part of the duplication; a tunnel under Blackheath was announced last year.

"We are looking at two options under Blackheath - a four-kilometre tunnel and a 4.5km tunnel option," he said.

"They [Mount Victoria and Blackheath] are both areas on the Great Western Highway where we see traffic building up after a long weekend, after school holiday periods."

Mr Toole pointed to the duplication of the Pacific Highway between Newcastle and the Queensland border, which was finally completed last year.

"We've now finished work on the Pacific Highway; we've got work going on at the Princes Highway [which runs along the South Coast].

"That is why we're now doing the work that is required for the Great Western Highway."

Mr Toole said the government knows the duplication of the Great Western Highway is "going to cost more than $2.5 billion".

"But that investment is going to give us short to medium term projects that are needed to improve that section of road," he said.

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