Diverging from the norm: Following the Bruce Highway upgrade

The motorway interchange is complete. The last remaining ramp connecting Sunshine Motorway motorists northbound to the Bruce Highway opened at the end of June. According to TMR, before construction began, the northbound exit between
Bruce Highway and Sunshine Motorway experienced regular congestion and a high crash record.

Diverging Diamond Interchange

While the standard diamond interchange is a familiar feature of Australian roadways, CR2SM project is the first project in Australia featuring a Diverging Diamond Interchange (DDI).

DDIs are a twist on traditional interchanges. The interchange design leads two directions of traffic to temporarily cross to opposite sides of the bridges, allowing for exiting vehicles to turn off easier, while those remaining on the road can continue on with less stops.

“The idea of the DDI was first floated during the tender phase,” says Whitaker. “DDIs have been used with great success in other countries, with almost 100 now operational worldwide. The majority of these are in the United States.”

“Traditional interchanges have right-turning lanes in the middle of the road and drivers must wait for oncoming traffic to pass before turning right. A DDI moves right-turning motorists to the edge of the interchange allowing them to turn right without giving way to, or blocking, traffic coming the other way. Synchronised traffic signals, line marking and signage guides motorists,” explains Whitaker.

First built in France in the 1970s, the DDI increases traffic efficiency and road safety through decreasing the number of stopping points.

“Incorporating the DDI at Caloundra Road significantly reduced the interchange footprint on the former Beerwah State Forest from 35 hectares to about six hectares, as compared against the footprint to the original reference design,” says Whitaker.

Tying in the vertical geometry from the existing ramps to the new DDI alignments was a project challenge that saw the east to west connection lifted by almost three metres.

The DDI replaced two of Caloundra Road’s loop ramps. This change saw the installation of traffic signals that increased the needed size of lane storage to 2.5 times what was existing. The lanes also had to be doubled when installing signals for the second loop which affected the east to west flow of traffic.

Whitaker notes that through TMR’s traffic performance modelling, the DDI shows to be providing better levels of service to commuters since its opening in December last year.

“The long traffic queues and the number of crashes have reduced,” says Whitaker. “In Australia, it [the DDI] is an emerging interchange form that responds to increased demand to find different ways to manage traffic volumes within budget and land constraints.”

Project challenges

The project has so far seen more than 22 construction stages and over 90 traffic switches with 13 of these switches occurring within one month and up to five concurrent switches occurring in a single night shift.

“With a constrained footprint to work within, high traffic volumes, significant variances in geometry and limited existing network capacity made staging, the number of switches and Temporary Traffic Management (TTM) logistically complex, even for a large project,” says Whitaker.

The project saw complex TTM staging and construction while teams still had to manage existing traffic numbers.

To overcome this, a dedicated team was appointed to oversee all aspects of planning for traffic switches with meetings being held at six, four, two and one weeks prior to the traffic switches being made.

Novel technologies

The DDI, however was not the only new innovation applied at the CR2SM. The Trimble SPS985 GNSS Rover linked to a Trimble GNSS base station; or more simply known as a Tiny Surveyor was also introduced during the project.

The Tiny Surveyor is a remotely operated machine that allows human surveyors to spot out line markings from a safe distance from the traffic site itself.

“It works up to 10 times faster than marking out on foot and uses far less paint than the previous manual method. Using GPS technology helps achieve an accuracy of two to three centimetres,” says Whitaker.

“A test of a 1.5-kilometre strip with three lines to mark out was completed in 90 minutes; this would normally take three surveyors four and a half hours to complete.”

Drones, or flying robots that can capture images were used by surveyors to capture aerial data and images, allowing for mapping and estimating traffic movements.

With application of these technologies developing greater understandings of how these machines work in real-world applications, Whitaker believes that novel technologies such as these will continue to be adopted within the construction industry, resulting in greater time and cost savings.

Flood immunity

Construction during the CR2SM saw above-average rainfall. With the Mooloolah River floodplain situated adjacent to the CR2SM project site, managing water that could damage nearby communities and environmental habitats was crucial.

It was here that another innovation, the high-efficiency sediment (HES) basin, was introduced. HES basins function by capturing storm water or tailwater, which is water with sediment runoffs, and adding clarifying agents to settle the sediments. Water can then be recycled for agriculture uses with the sediments potentially returned to productive land.