The alternative route between the Bathurst region and Sydney, the Bells Line of Road, was closed in both directions 13 times over the same period.

As debate continues between the Nationals and the NSW Government over which side has the better plan for an upgrade of the road between Katoomba and Lithgow, the Western Advocate contacted the Transport Management Centre (TMC) to see just how regularly the highway is being shut off.

According to the TMC, there were 40 total road closures (when the highway was closed in both directions at a particular point, as opposed to being closed only in one direction) at various locations between Penrith and Lithgow between January 2019 and January 2024.

Three of these complete closures were the result of scheduled roadworks, two were for special events and the other 35 were the result of road incidents or "adverse weather events".

A map plotting the various closures, provided by the Transport Management Centre, shows clusters around Katoomba, Mount Victoria and the Forty Bends area near Lithgow.

The Great Western Highway's lack of reliability was one of the justifications for the proposed duplication of the road from Lithgow to Katoomba that has been put on hold since a change in government at state and federal levels.

The duplication of small sections at Medlow Bath and Little Hartley are going ahead, though.

A mid-2021 scoping report for the then-proposed upgrade of the highway between Blackheath and Little Hartley described that section as "vulnerable to closure" and said "contraflow measures cannot be established due to the single lane alignment, resulting in major delays in the event of an incident".

In terms of Bells Line of Road, the TMC said there were 13 total closures between January 2019 and January 2024, all of which "resulted from adverse weather events or traffic incidents".

A map of the closures on Bells Line shows a cluster between Kurrajong Heights and Kurrajong on the eastern end of the road.

The data and map from the TMC does not include Bells Line's most recent closure, on Saturday, February 24, due to a fallen tree and power lines.

On that occasion, the road was closed in both directions at Mount Tomah from 7am until 2.30pm, when one lane reopened.

Motorists were advised to use the Great Western Highway in the meantime.

TRANSPORT for NSW regional director west Alistair Lunn said last December that the organisation would consider a number of factors as it planned its next investment on the Great Western Highway.

"We look at where we have accidents, where we have resilience issues - so slope failures, bushfires really impact that corridor," he said.

"We also look at where there are congestion points - obviously, Blackheath has congestion and [there's] the flow-on that has around Mount Victoria.

"But also between Medlow Bath and Katoomba, there are sections there where the detour, if a tree falls down or a powerline [falls down] in windy conditions or we have icy conditions or an accident, the detours are quite long.

"So that's how we prioritise."