The New South Wales (NSW) government closed Mitchell’s Causeway, an artificial bridge along Victoria Pass built by convicts centuries ago, after Transport for NSW’s ongoing asset management program identified significant deterioration in the earth and rubble fill within it.
The authorities installed equipment within the road’s surface and in its sandstone walls to proactively monitor movements in real time and collect extensive data on the substructure’s condition.
The state government’s decisive move to close this section of the Great Western Highway might have averted disaster, especially since it descends from Mount Victoria to Little Hartley.
Although the closure has disrupted local communities, the rebuild promises long-term convenience for road users and the mindful preservation of the heritage structure for posterity.
Building a new bridge
The NSW government is constructing a concrete deck with an asphalt finish to serve as a new platform. Deep concrete piles drilled through the old causeway and anchored into solid bedrock support the new structure.
Poured concrete will fill steel reinforcement cages, creating a strong foundation that allows the deck to sit above and independently of the convict-built causeway.
The concrete piles transfer the traffic load to the underlying bedrock, which the authorities have confirmed remains strong. Transport for NSW finalised the design and contract in 109 days after completing three key steps:
- Completing meticulous geotechnical testing
- Convening a global industry roundtable
- Running an accelerated procurement process involving Australian and international engineering experts
Road users can expect new safety barriers once this vital corridor between the Central West and Sydney reopens in the second quarter of 2027.
To make the most of the Victoria Pass closure, the transport services and roads agency is carrying out various works on the site, where possible. Pavement updates, drainage improvements and guardrail upgrades help neutralise the geohazards common in mountainous terrain and steep corridors, such as mass movement and erosion, which should strengthen the crossing once it becomes accessible to the public again.
Noise from construction activities may affect nearby communities. The augers used for drilling can be as loud as leaf blowers and blenders. Transport for NSW acknowledges that noise pollution can be disruptive and aims to minimise disturbance by taking breaks between noisier activities and scheduling louder activities for daytime. Still, the construction crew may have to work around the clock to fast-track the project and reopen the road sooner rather than later.
Preserving the heritage structure
Mitchell’s Causeway is a heritage-listed site after being referenced in the NSW Government Gazette on March 8, 2024. The listing is a formal recognition of the structure’s significance to the state, indicating that it’s worthy of preservation.
The history of the causeway dates back to 1830, when Surveyor-General Thomas Mitchell identified the site at Mount Victoria as part of a more direct route to Bathurst that avoided the Mount York descent. The site spanned a deep ravine flanked by two rocky outcrops, requiring a stone causeway to cross it.
Convict iron and road gangs carried out the construction work. The project began in January 1830 without permission from Governor Ralph Darling. The situation angered Darling, especially since Mitchell had to abandon an ongoing project and relocate the crew to work on the new route. After a heated back-and-forth between Darling and Mitchell, the governor capitulated. Construction work was in full swing by September of the same year under the supervision of Mitchell’s assistant surveyor.
After two and a half years of labour-intensive work, the causeway officially opened in October 1832. The original design only included a simple parapet, and the authorities have added a road surface, balustrade and Armco railings since. Nearly 200 years later, most of the road still stands, despite becoming subject to extremely heavy traffic.
The causeway’s history and longevity are enough reasons for it to merit preservation. It also features rock engravings within 5 metres of the shoulder edge. Their shallow depth and rough form convinced experts that they were graffiti made by the workers.
While the inscriptions don’t appear in official documents, the engravings seem to mean “bridge men.” Transport for NSW is working closely with the Department of Heritage to minimise the impact of reinstatement works, helping preserve what remains of its original features and the marks of those who built it.
Promoting the old Causeway’s resilience
The new elevated road bridge is a permanent solution for reinstating the highway. The government is building its deck on the existing alignment while its deep concrete piles transfer the traffic loads into the stable bedrock, reducing the pressure on the sandstone walls.
Moreover, the authorities are planning to add another eastbound climbing lane in the future. The extra lane would increase capacity along the renewed crossing, especially since freight operators depend on the corridor, and improve traffic flow for fast-moving vehicles.
Regarding heritage bridge restoration, stabilisation and grouting works should strengthen Mitchell’s Causeway. Together with the construction of the new deck, the government’s collective effort should improve its long-term resilience for preservation without repurposing it, as has been done with other structures with architectural heritage, such as 500 Bourke Street.
Mitchell’s Causeway as a case study in heritage infrastructure preservation
The closure of Victoria Pass has forced motorists to take detours that prolong commutes and sometimes make the trip more dangerous. Nevertheless, the Great Western Highway closure helps manage a more serious risk, as a structural collapse would have far greater consequences for road users and nearby communities. Identifying defects in Mitchell’s Causeway early and developing a permanent solution in a short period supports both road safety and heritage site preservation.
