Flexible barriers: How they work and the 'cheese cutter' myth

Flexible barrier being installed on the Melba HighwayImproving road infrastructure is a vital part of the Towards Zero approach. $1 billion is being invested into making Victorian roads safer for people to use in the Safer System Roads Infrastructure Program (SSRIP). As part of SSRIP a number of centreline wire rope safety barriers, or flexible barriers as they are also known, are set to be installed on high risk rural roads.

Find out more about SSRIP.

Flexible barriers can stir up emotive debate about their effectiveness at protecting road users and the potential risks for motorcyclists. While some concerns are valid, at times a misinterpretation of facts surrounding flexible barriers has people worried. Below, we address many of the concerns and questions raised about flexible barriers based on research conducted in Australia and overseas.

What are Wire Rope Safety Barriers and how do they work?

Wire Rope Safety Barriers, also known as flexible barriers, are road barriers made up of four tensioned wire ropes supported by steel posts. They are described as 'flexible' because they stretch and absorb the force of the crash. The barriers use a dual mechanism to slow down and divert excessive force away the people inside the vehicles. The ropes deflect and absorb the energy and the posts collapse, slowing down and redirecting the vehicle away from the hazard with very little rebound. The flexible barrier is the most forgiving system with people more likely to walk away after their car crashes into it than other available road barriers.

How are they tested?

Most flexible barriers are developed around the world. VicRoads assesses and accepts different products based on the US examination standard because they have a similar mix of cars on the road to Australia (from smaller to heavy vehicles).

The tests simulate the worst practical conditions of crashes with the barrier in terms of angle and speed. They include:

-          820kg car (eg a smart car) travelling at 100km/h hitting the barrier at a 20 degree angle

-          2000kg car (eg a ute) travelling at 100km/h hitting the barrier at a 25 degree angle

-          8000kg truck (eg a heavy rigid truck or bus) travelling at 80km/h hitting the barrier at a 15 degree angle. The video below demonstrates one of these tests.


Why are we installing flexible barriers?

There are three types of barriers that we generally see on our roads: rigid concrete barriers, semi-rigid Steel W-beam barriers and flexible wire rope safety barriers. Research conducted by Monash University Accident Research Centre (MUARC) shows that flexible barriers are superior compared with concrete and Steel W-beambarriers because of the way they dissipate the energy of the crash away from people in the cars, their deflection levels and the way they contain the vehicle. Centreline wire rope barriers are now being specifically used and are effective at preventing head-on crashes, i.e. when a vehicle crosses the median strip into oncoming cars (such as in the Towards Zero Now & Then ad).

Loss-of-control crashes are a major contributor to deaths and serious injuries on our roads. MUARC's research evaluated 100km of wire rope barrier across Victoria and their findings suggest they are responsible for significantly reducing the risk of death and serious injury in crashes. Their results, consistent with studies conducted overseas, estimate all crashes have been reduced, including run-off-the-road and head-on crashes, on individual routes upwards of 75%. On the Hume Highway and Eastern Freeway the estimation is even greater, up to 87% and 83% respectively.

At the end of the day, you are more likely to walk away – or as the below photo shows, drive away – from a crash with a wire rope safety barrier than any other barrier system.

Collapsed wire rope safety barrier at Anthony's CuttingThe photo comes from the Melbourne bound carriageway of the Western Highway at Anthony's Cutting. Here the flexible barrier has stopped a vehicle from crashing over a steep embankment with potentially deadly consequences. Instead the vehicle was able to drive away from the site without intervention from VicRoads (i.e. VicRoads don't have any driver or vehicle details relating to the incident).

Note: VicRoads regularly inspects the road network yet they may not be aware of new hazards that arise. Find out how you can report hazards, including barriers that need to be repaired.

Aren't they banned overseas due to concerns about dangers to motorcyclists

There is a common misconception that flexible barriers are banned in some places in Europe because of the danger they pose to motorcyclists; this is not the case. In countries such as Denmark and Norway, governments have either ceased installation or banned the barriers due to political pressure from lobby groups. But, there is no scientific research to show flexible barriers cause more deaths and serious injuries for motorcyclists. Swedish studies have shown there is actually a 40 – 50% reduction in risk of being killed for motorcyclists with wire rope safety barriers. Flexible barriers are being installed world-wide by countries seeking to reduce trauma on their roads, including Sweden, the USA, New Zealand and Australia.

The 'cheese cutter' myth

The 'cheese cutter' myth is thought to have been spread after an incident in New Zealand where 21-year-old Daniel Evans was fatally injured striking a road side wire rope safety barrier. News reports at the time suggested the wire rope barriers presented a similar danger to other motorcyclists. On reading the following coroner's report about Daniel's death it was found that speed was a major factor. It was calculated Daniel was travelling between 148 – 190km/h when he left the road, which resulted in an impact speed the equivalent of jumping off a 13-storey building.

While barriers of all kinds are designed to protect people from hazards, either on the side of the road or from oncoming traffic, they still pose a risk to the vulnerable human body and experts acknowledge their risks. Motorcyclists are particularly vulnerable to injury in all crashes due to the limited protection their bodies have (similar to that of a pedestrian) compared to someone in a vehicle.

Flexible barriers pose a risk to motorcyclists because of their steel posts rather than the wire rope as commonly thought. (W Steel barriers also have this risk.) The posts are designed to bend for vehicles, but not people, and generally, motorcyclists will come off their bike and slide under the wire or into a post. Raphael Grzebieta is currently the professor of Road Safety at the Transport and Road Safety (TARS) Research unit at University of New South Wales and has done extensive research on wire rope barriers and motorcycle crashes. In the coroner's report into Daniel's death he is quoted as saying:

"The term 'cheese cutter' refers to the performance of roadside barriers made of cable wire rope or high tension wire held by posts. The idea of the 'cheese cutter' effect is a 'myth'. It appears that group of misinformed motorcyclists perceive these types of roadside barriers as a hazard providing less safety than other barrier systems such as concrete or guardrail systems.

"There is no evidence to date anywhere in the world of motorcycle riders travelling at or below the posted speed limit, and who has crashed into a wire rope barrier, being cut by the wire rope in a manner similar to how cheese is cut with wire…"

In Sweden, a survey of more than 600 km of flexible barriers on their roads had no record of motorcycles being 'sliced' by the barriers. Instead they have seen a 40 – 50% reduction in risk for motorcyclists being killed since introducing wire rope safety barriers. That being said, flexible barriers are not the barrier of choice for routes used heavily by motorcyclists or on tight curves; those without exposed posts such as Steel W-beam attached with motorcycle rub rail are the preference, but these offer less protection than flexible barriers to vehicles and their occupants. Where new flexible barriers are installed in Victoria, they are fitted with cushioning and posts can now be created to have a wider surface area to lessen the impact force. Where needed, motorcycle friendly products (such as frangible signs, sign supports and guide posts) and motorcycle protection devices (such as stack cushions for WRSB posts) are also installed. Research is also currently being conducted to find a way to shield the posts or find alternatives without compromising the barriers' benefits.

Flexible barriers also prevent motorcyclists being injured by other vehicles too. In the below video, filmed on one of Sweden's 2+1 roads, the wire rope safety barrier stops a car from having a head-on crash with a motorcyclist riding in the opposite direction.

Find out more about what riders and non-riders can do to protect our motorcyclists.