The main road linking Sydney to western New South Wales has shut after cracks were detected in a bridge built by convicts.

The Great Western Highway is now closed in both directions and there is no timeline for when it will reopen.

Initially, it was set to be impacted for four days.

Transport for NSW (TfNSW) said it was “an evolving and complex situation”.

On Thursday, eastbound lanes at Victoria Pass, near Little Hartley, were shut when damage was detected in the road surface of Mitchell’s Causeway, known as The Convict Bridge.

But overnight on Sunday, westbound lanes were also closed after geotechnical crews identified major issues.

Deputy secretary for road maintenance and resilience Matt Fuller said assessment teams had been working over the weekend to determine the risk.

“We’ve identified further cracks in the pavement and our geotechnical information and monitoring has confirmed there’s movement in the road’s substructure,” he said.

The heritage structure was built by convicts in the 1830s and forms part of the steep, windy thoroughfare used by thousands of vehicles daily.

“Given those sensitivities and obviously with the overriding consideration of safety, we’ve taken the precaution to close both lanes,” Mr Fuller said.

“We understand that’s going to be frustrating for motorists and we certainly appreciate their patience and understanding,” he said.

Motorists travelling eastbound, towards Sydney, are being diverted through Lithgow via Chifley Road to the Bells Line of Road or the Darling Causeway.

People travelling westbound are being detoured along the Darling Causeway at Mount Victoria to the Bells Line of Road and Chifley Road.

Roadworks are also taking place on the diversion roads, which is adding to the congestion.

Approximately 11,000 vehicles travel on the Great Western Highway between Little Hartley and Lithgow each day, according to TfNSW.

About 1,800 of them are heavy vehicles.

The closure is a major problem for truck drivers, with restrictions on heavy vehicles through the main street of Lithgow.

NSW Regional Roads and Transport Minister Jenny Aitchison said by Saturday, engineers were feeling positive the road would reopen by Tuesday.

“But last night they saw some cracking actually opening … they could see it visually that there was opening cracks and they were quite concerned about that,” Ms Aitchison said.

“While that’s happening, while there’s still movement on the slope we have to use an abundance of caution.”

Highway headache politics

The need to improve the road link to the state’s west has been a long running political issue that locals have been dealing with.

Shadow Minister for Regional Roads and Transport Paul Toole said commuters had reported having one to two hours added to their trips due to the diversions and congestion.

“It’s caused major confusion and chaos,” Mr Toole said.

“That impacts on productivity, it impacts on people having appointments and getting to Sydney, missing timelines they require.

As the state Member for Bathurst, Mr Toole has been highly critical of the state government for abandoning the NSW Nationals’ plans for the 11-kilometre Great Western Highway Tunnel.

From Blackheath to Little Hartley, it would have traversed the land beneath Victoria Pass.

“We saw the federal and state Labor governments rip $4.5 billion out of any of the upgrades or work that was required for the tunnel on that section of the road,” he said.

The tunnel itself had not been funded or definitely costed under the NSW Coalition, but was estimated to have a price tag of $8 billion.

In 2023, when the state Labor Party vowed to pause the project, it said the cost had blown out beyond that to approximately $1 billion per kilometre for the tunnel.

But Mr Toole said the state government had not come up with a viable alternative, which is proving to be a critical error.

“We’re not seeing any improvements. We’re continually seeing the road closed week after week,” he said.

“We need to make sure that have a road corridor that is fit for standard, but is also going to continue to meet the growing needs and demands of our communities.”

The state government’s recently released White Paper for Sydney to the Central West set out its plan for the road corridors.

In it, Ms Aitchison described the former Coalition’s plans for the tunnel as a “fantasy”.

“They announced a megaproject they never properly funded, never finished planning and never intended to deliver,” she said.

“Then they walked away, leaving the Blue Mountains and Central West to deal with the consequences.”

The White Paper instead lays out other road upgrades, speed limit changes, making the roads more resilient, improving rail services and freight efficiency.