Roads & Infrastructure Magazine speaks to Monash University’s David Logan about the lifesaving effects of flexible safety barriers on Australian roads.
Travelling on regional roads can come with additional risks, with motorists five times more likely to be seriously injured or suffer a fatality compared with metropolitan roads, according to the Victorian Transport Accident Commission (TAC).
The TAC says the majority of these crashes are due to drifting vehicles that run off the road and collide with other motorists or a roadside object at speeds of around 100 kilometres per hour.
Dr. David Logan, Senior Research Fellow at the Monash University Accident Research Centre (MUARC), says the high speeds on country roads poses additional risks to drivers.
“Modern passenger vehicles with an Australasian New Car Assessment Program (ANCAP) safety rating are crash tested at 64 kilometres per hour in a frontal offset crash. However, when travelling at 100 kilometres per hour there is more than double the energy involved in the crash which means collisions have an increased severity and a significantly higher chance of causing serious injury or fatal outcomes.”
To protect motorists in these conditions, wire rope safety barriers are being installed on high traffic country roads and have been found to reduce these crashes by 85 per cent.
What is unique about a flexible safety barrier compared with a rigid barrier is their ability to catch vehicles that collide with it. The system absorbs the energy with a system of steel rope supported by collapsible posts that slows the vehicle down in a controlled way, to the point where the driver can bring the vehicle safely to a stop and the vehicle airbags are less likely to deploy to deploy.
In contrast, when a vehicle collides with a W-beam steel barrier or concrete barrier, the energy is usually absorbed by the car, which is deflected across the road. This has the potential risk of injuring the vehicle occupants, impacting other motorists and causing further crashes.
In Victoria, wire rope safety barriers must conform with the requirements of the Australian Standard AS/NZS 3845 Road Safety Barrier systems and must pass crash testing in accordance with the recommended procedures for the safety performance evaluation of highway features, developed by the United States National Cooperative Highway Research Program to at least Test Level four.
According to the TAC, they are able to withstand the impact of passenger vehicles weighing up to 2000 kilograms at 100 kilometres per hour and larger vehicles weighing up to 8000 kilograms travelling at 80 kilometres per hour.
Because of their effectiveness at improving safety, state road authorities around Australia have implemented flexible safety barriers to protect motorists from some of the most common crash scenarios.
Bernard Carlon, Executive Director of the NSW Centre for Road Safety says wire rope safety barriers require more deflection than semi-rigid barriers and are designed to result in less damage to the colliding vehicle through better dissipation of energy.
“When properly designed, flexible safety barriers should reduce the severity of crashes that involve straying vehicles,” Mr. Carlon says.
“Research and crash testing of flexible safety barriers have consistently shown a reduction in crash severity for vehicle occupants by up to 95 per cent along both roadside and median installation.”
Long straights of road tend to be the optimal place for road safety barriers, which usually have a break positioned every 500 to 1000 metres to provide access to emergency vehicles.
Data from NSW Roads and Maritime Services (RMS) shows around 900 kilometres of flexible safety barrier has been installed on the NSW state road network.
In February 2018, NSW Minister for Roads Melinda Pavey announced the Road Safety Plan 2021 and committed to installing an additional 300 kilometres of targeted safety works, such as flexible, wire rope barriers as part of the state’s $640 million Saving Lives on Country Roads program.
In NSW, the cost per kilometre for wire safety barriers varies between $5000 to $20,000 depending on the type of barrier and will generally cost less than rigid barrier systems. However, the overall cost of installing a wire safety barrier tends to be relatively similar due to the cost of project development, traffic management and installation.
The Victorian Government’s Towards Zero Action Plan 2016-2020 has invested more than $1 billion over five years to reduce fatalities by 20 per cent and serious injuries by 15 per cent. It maps out the installation of 2000 kilometres of flexible safety barriers along the state’s most high risk regional roads.
To discover the barriers’ capabilities in a real crash environment, the TAC initiated tests on an actual road with the assistance of the MUARC as a technical advisor.
Dr. Logan said that most crash tests are performed with unmanned vehicles at severe angles to push barriers to their limits, but these often don’t provide examples of how they would help in more
“The test occurred near Tatura, close to Shepparton, where a vehicle was driven along a straight stretch of highway by a stunt driver at 90 kilometres per hour. The driver then began a simulated drift of seven degrees, which we found was typical in a fatigue-related crash from our real-world crash investigations,” he says
“The vehicle impacted just past one of the posts and rapidly decelerated knocking down 17 posts over 35 metres. The vehicle separated from the barrier at 20 kilometres per hour and didn’t cause the airbags to deploy or result in any injuries.”
The test was filmed from a number of different angles and recreated one of the most common types of crash. Footage from the test will be used in a publicity campaign about the barriers and what they’re capable of.
Dr. Logan says flexible wire safety barriers do have a downside. Once a vehicle has impacted with a barrier, the section can’t function properly as the wire becomes slack which means the system requires a diligent maintenance and repair program.
“During the crash test, the 40-metre section was quite damaged. However, it was able to be fixed within two hours of the impact,” he adds.
Mr. Carlon says repair of wire rope safety barriers is relatively simple which reduces traffic disruption during maintenance.
To ensure the barriers are functional, RMS advises that temporary repairs to safety barriers must be actioned within three to seven days, with all emergencies and incidents that are hazardous actioned immediately. These repairs are scheduled and prioritised by local managers in accordance with the published specifications.
VicRoads similarly prioritises barrier repairs based on the amount of damage and its location. The severity of the hit can often impact how long the barrier will take to fix and in some cases a few barrier posts may need to be replaced and the wire retensioned.
Dr. Logan says the flexible safety barriers are the best solution currently available to continue moving around country regions at current highway speeds.
“We have made huge progress towards eliminating road trauma in Victoria and must continue to use research evidence and practical solutions to ensure no road user is killed or seriously injured on our road system.”