Instant road

from Roads & Infrastructure February 2020

Rubber hits the road

CREATING AN INSTANT ROAD

DISASTER STRUCK THE SILVER CITY HIGHWAY WHEN THE BUNNERUNGEE BRIDGE CLOSED DUE TO A STRUCTURAL ISSUE, FORCING A NINE-HOUR DETOUR, BUT TRANSPORT FOR NSW STEPPED IN TO CREATE AN INSTANT ROAD OVER THE ANABRANCH.

With just 26 recorded residents, Scotia, NSW, relies on the Silver City Highway for its connection to the rural city of Wentworth.

The Bunnerungee Bridge is situated about 65 kilometres north of Wentworth on the Silver City Highway, linking Wentworth with Scotia by enabling passage over the Great Darling Anabranch.

In late October 2019, a structural issue was found on the bridge during routine maintenance, forcing its closure. The shutdown resulted in a nine-hour diversion for traffic as the Silver City Highway is the main road connecting the two towns.

While the area surrounding the Bunnerungee Bridge is not densely populated, it remains an important agricultural region, so a solution was needed.

Transport for New South Wales organised the instant road with the help of local councils and contract workers.

Transport for NSW Director for the SouthWest Lindsay Tanner says an engineering feat was achieved when a side track was built and open to traffic in eight days.

“As fatigue-related crashes are twice as likely to be fatal, imposing a lengthy detour was not considered safe or efficient,” Ms. Tanner says.

Within 24 hours of the fault’s discovery, Transport for NSW carried out an inspection and analysis to determine the possibility of building the side track.

Transport for NSW also carried out environmental assessment in conjunction with Dareton Local Aboriginal Lands Council and a basic design to determine a safe layout for the side track.

“Road designers took into account the alignment of an appropriate side track, using satellite information to determine grade and existing surface levels for road construction,” she says.

Existing disturbed land and tracks next to the bridge were then used to construct the side track over eight days.

Electronic messaging suppliers and traffic control contractors were also brought in to ensure road users were given as much notice of closures, delays and detours as possible.

The key initiative for the construction of

the instant road was to find a way to get a foundation through the waterway using geotextile to support the pavement.

Once the soil foundation and geotextile were laid, the gravel track was opened to light vehicles, eight days after the bridge’s closure. The road was sealed the following day, allowing all vehicles to continue along the Silver City Highway. A team of around 10 Wentworth Shire council staff were enlisted to build the instant road, which Ms. Tanner says was an incredible effort considering the challenges they faced.

The Wentworth to Broken Hill pipeline constrained the project footprint, restricting the use of vibration compaction. There was no phone reception, even for satellite phones, at the site, and its remote location meant there was limited access to construction materials.

During the eight days it took to construct the instant road, there were some challenges for vehicles using the lengthy detour.

Trucks faced a restriction at an alternative bridge over the Murrumbidgee River at Hay. The Hay bridge is not heavyvehicle-compliant and, as such, was only used for passenger vehicles.

“Transport for NSW allowed these vehicles to access the bridge while the detour was in effect,” Ms. Tanner says.

Traffic lights guided vehicles over the bridge, one at a time under reduced speed limits, in order to reduce impacts. Following the completion of the side track, Hay Bridge was returned to normal operation.

Ms. Tanner says Transport for NSW is committed to getting the Bunnerungee Bridge operating at full capacity as quickly as possible.

A team of workers is completing initial repairs to the bridge now, with its expected reopening set for this year .