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Study analyses bull bar safety

Australian Standard for bull bar design proved to be safer in university study

30 Oct 2014

SOUTH Australia’s state government believes the findings of a University of Adelaide study into bull bar safety have vindicated last year’s move to join New South Wales in mandating Australian Standard compliance for new vehicle bull bars.

The study, carried out by the university’s Centre for Automotive Safety Research (CASR) and funded by the South Australian department of planning, transport and infrastructure, examined the differences between pedestrian impacts with vehicles using bull bars meeting and in contravention of the Australian Standard.

Bull bars conforming to AS4876.1-2002 – angled rearward and designed to follow the contour of the vehicle’s shape – were found to pose upwards of 50 per cent less risk of serious head injury in pedestrian impacts than nonconforming designs due to the lower speed and force with which the pedestrian’s head impacts the bonnet.

Designs that conform to the standard were also found to cause less chance of pelvic injuries, but with slightly greater risk of upper leg injuries as the trade-off.

Construction material was also considered, with steel bull bars posing the greatest risk of serious head injury, followed by alloy or polymer depending on the design of nonconforming bull bar.

CASR associate professor Jeremy Woolley said the research shows South Australia’s adoption of the bull bar standard “was a step in the right direction”.

Australian Automotive Aftermarket Association executive director Stuart Charity also supported the move and called for national adoption of both sections of the Australian Standard.

Using MADYMO simulation software, researchers created models based on 2006 versions of a Nissan Patrol SUV and a Holden Commodore sedan, with three bull bar designs, one being Australian Standard compliant and the other two nonconforming with the top and lower bars in parallel or the upper bar forward of the lower bar.

Each design was modelled in alloy, polymer and steel for both vehicle types, with an initial impact speed between the bull-bar and pedestrian of 40km/h and 0.75g of deceleration applied during the entire simulation to represent emergency braking.

Nonconforming designs with the upper bar placed forward – as per the archetypal ‘feral’ ute – were found to be most hazardous, especially when made from steel or alloy.

Parallel bull bars were least risky in alloy, with the slight increase in risk for polymer construction similar to that of the forward design. But steel parallel bull bars posed significantly higher risk than the forward type of both alloy and polymer forward type of construction.

According to Adelaide news website InDaily, the report’s co-author Sam Doecke acknowledged the fact a vehicle with no bull bar is safer for pedestrians but said bull bars conforming to the Australian Standard could be “relatively pedestrian friendly”.

South Australian road safety minister Tony Piccolo told InDaily the study showed the government “made a very good decision”.

“Just to reassure the market that we were doing the right thing, research was undertaken to show that it actually does achieve a good balance.

“(The compulsory standard) improves road safety for pedestrians, and at the same time, it doesn’t reduce the efficiency of protection for the vehicle and the driver.”

Limitations to the study included a lack of consideration for differences in contact stiffness across the vehicle’s bonnet, which can be affected by supporting structures and hard surfaces in the engine bay, the omission of possible injuries to the pedestrian once they impact with the road after being hit by the vehicle and the model’s use of just one pedestrian type, hit at one speed and in one position in all tests.

In 2007 New South Wales was the first state to mandate Australian Standard compliance for all bull bars fitted to models first manufactured after December 31, 2002.

A crackdown on nonconforming bull bars in August this year led to the discovery that many people with offending accessories were unaware of the non-conformance or had been told by the manufacturer or supplier that they did comply with Australian Standards.

This was largely due to AS4876.1-2002 providing only general guidance for bull bar design with drawings rather than detailed specifications.

As a result the NSW state government issued an exemption order in September giving vehicle owners two years’ grace to investigate and, if necessary, replace, their nonconforming bull bars – although obviously nonconforming bull bars are still subject to enforcement.

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