Flexible Wire Rope Safety Barriers
Wire Rope Safety Barriers (WRSB) – Fast Facts
- Why Wire Rope Safety Barriers? They are effective at stretching and absorbing the force of a crash
- During impact, the posts bend close to the ground, and the ropes release from the post assisting the vehicle to divert excessive force and slow down
- Tested for three types of vehicles: small passenger, large passenger, and light truck
- Information for motorcyclists and the cheese cutter myth
- Wire Rope Safety Barrier Technical Facts
- Report Broken Barriers - visit the VicRoads website or call VicRoads on 13 11 70
- List of Victorian Roads being upgraded from 2017
Improving 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. The Safe System Road Infrastructure Program (SSRIP) is a partnership between the TAC and VicRoads to deliver safe road infrastructure throughout Victoria. Wire rope safety barriers are being installed in the centre of high-risk rural roads as they are a proven treatment to save lives on our roads. They prevent vehicles from leaving the road, and potentially hitting unforgiving roadside objects or rolling over.
Why use Wire Rope Safety Barriers?
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 from 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. Research has proven the wire rope safety barrier as the most forgiving system, with people more likely to survive than other available road barriers.
After significant research by Monash University Accident Research Centre (MUARC) into Wire Rope barriers, the findings demonstrate they can significantly reduce the risk of death and serious injury in crashes. It shows that flexible barriers are superior, compared with concrete and Steel W-beam barriers, because:
- they dissipate the energy of a crash away from people in cars and
- the way the rope deflects and contains the vehicle from hitting other objects (such as trees and other vehicles). See the Now and Then commercial below.
How Wire Rope Safety Barriers are used:
- In the centre of the road, they are very effective at preventing head-on crashes, i.e. when a vehicle crosses the white line in the middle of the road or the grassed median strip into oncoming cars.
- For loss-of-control crashes, particularly on country roads, like running off the road, or head on crashes - both major contributors to deaths and serious injuries.
- To make it more likely for people survive by diverting a vehicle away from road side hazards, which are proven to be very unforgiving and dangerous.
What happens on impact with a flexible barrier?
- During impact: The posts bend near the ground, and the ropes release from the post, depending on how big the impact is, this could include 10-15 posts
- After impact: The vehicle is typically redirected away from road side hazards which are potentially very dangerous and can lead to serious injuries or death
Once the safety barrier damage has been reported, the VicRoads maintenance team attend the site and repair the barriers. VicRoads staff regularly inspect the road network, however may not be aware of new hazards, so it is important to report them. Call 13 11 70 to report damaged barriers or visit the VicRoads website
How are the barriers tested?
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 rope heights are designed so that at least one rope will engage the vehicle for a large number of bumper shapes and they are designed at different heights because the barrier is tested with three different ‘worst case’ vehicles:
- 5th percentile small passenger vehicle
- 95th percentile large passenger vehicle
- 8T light truck i.e., moving van (see video below)
The 'cheese cutter' myth
The 'cheese cutter' myth is thought to have been spread after an incident in New Zealand where a 21-year-old rider was fatally injured after striking a roadside wire rope safety barrier.
News reports at the time suggested the wire rope barriers presented a similar danger to other motorcyclists. However, the coroner's report found that speed was a major factor. It was calculated the rider was travelling between 148–190 km/h when he left the road, which resulted in an impact speed the equivalent of jumping off a 13-storey building.
Professor Raphael Grzebieta 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 the motorcyclists 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…"
More information for motorcyclists
It's important to understand that motorcyclists are among the most vulnerable road users on our roads - this is mainly because they:
- do not have sufficient protection against external forces if a collision occurs
- travel at speeds not compatible with their level of vulnerability
- share the road with vehicles of significantly greater mass - this puts them at a disadvantage if a collision occurs
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. Motorbike riders 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. 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.
In Sweden, a survey of more than 600km 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. However, flexible barriers are not the barrier of choice for routes with higher motorcycle risks 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.
In higher motorcycle risk areas 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 sign supports and guide posts) and motorcycle protection devices (such as stack cushions for Wire Rope Safety Barrier posts), are also installed.
Research is also being conducted to find a way to shield the posts or find alternatives without compromising the barriers' benefits. Future research and innovation will hopefully help us to provide more safe solutions for our motorcyclists.
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.
What are they made from and how do they work?
- The steel posts and cable are manufactured here in Australia. This makes up the majority of the system. Other smaller components such as the plastic spacers and caps are manufactured in Europe (with the proprietary system owner).
- Called 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 from the people inside the vehicles.
- The Wire Rope Safety Barrier is made from normal steel. The steel post is 4mm thick and has been galvanised to meet a 20-year design life. At ground surface, there is an addition steel stiffening plate to reduce bending of the post.
- The ropes are 19mm 3x7 strand galvanised cable and are separated within the post by a plastic spacer, to ensure the ropes sit at the desired height when a vehicle impacts.
- Just below the top rope, there is a stainless steel stiffening frame and wire hook. This is to hold the bottom three ropes within the post and against the vehicle until there is enough engagement that the hook releases.
- This ensures the ropes do not release too early and fall below the vehicle or are forced over the top.
- The Wire Rope safety system is built to redirect and absorb energy to protect human bodies. Part of the system is to apply tension to the ropes which absorbs this energy.
- The tension is applied using a tension machine and hand-pump, to achieve the correct level of tension on the wire ropes, during installation. This tension is maintained by VicRoads.
Why are the posts at different spacing?
- The Wire Rope Safety Barrier posts provide lateral resistance during an impact. Therefore more posts will have less barrier deflection. This is critical when the hazard is quite close to the barrier. On the other hand, greater post spacing will cause greater deflection which can be more forgiving for the vehicle occupant, however:
- The Wire Rope Safety Barrier posts also keep the ropes close together until there is enough force to release.
- A very large post spacing can have issues where the vehicle impacts mid-spacing, and there are no posts to hold the ropes against the vehicle hence there is a maximum post spacing applied to the installation.
- 2.0m-3.0m post spacing maximises these two performance elements.
- 5.0m is being investigated currently as the absolute maximum spacing.
What do they cost?
The typical supply and install cost used to be around $120/metre, however, given the engagement and efficiencies developed over the last couple years, the current cost is around $70-$80/metre however these can vary depending on the complexity of the roadside being fitted with flexible safety barriers.