The problem with wire rope safety barriers

Many would agree that some of the worst road trauma is as a result of head-on collisions, closely followed by accidents involving trees and telephone poles, on high speed stretches of road. But wire rope safety barriers that are designed to protect motorists are also causing some of the worst road trauma. News reports and photographs of accident scenes, along with now infamous TAC commercials re-creating these events, are no doubt burned into the brain of many Australian motorists. And perhaps it's images like these that have underwritten the rise of wire rope safety barriers in Australia.  

How do wire rope barriers work? 

Wire rope safety barriers (wire barriers), also known as flexible barriers or cable fences, are highly tensioned wire ropes, supported by steel posts. The barriers are designed to slow or stop wayward vehicles by absorbing their impact and, in doing so, reduce major off-road and head-on collisions on our roads.     

Wire rope barriers are quick and easy to install and are, at least in the short term, relatively cheap - which is why rope wire safety barriers can be found on many roads across Australia.

The use of wire barriers is increasingly popular, as shown by a recent government announcement that a further 330km of the barriers are to be installed in Victoria alone in the coming year (at the time of writing).

So, what's the problem with wire rope safety barriers?

"In some areas wire barriers are pretty good, but if you're not careful where you put them they can be incredibly dangerous" says road safety expert and Australian Motorcycle Council spokesman, Guy Stanford.  

Motorcyclists, in particular, have raised concerns that wire road safety barriers can act as a "cheese cutter" when riders fall or slide into them. But, according to Stanford, "The biggest problem is the vertical posts. Upright objects are a motorcyclists' worst enemy. Whether it's a tree, a telephone pole or a post in a fence, where there's an upright, that's where the force is concentrated and that's what kills or seriously injures riders."    

Do wire rope safety barriers pose a risk to all drivers?

It's not only motorcyclists who are put at risk where wire barriers are unsuitably installed. Their effectiveness relies on the wire remaining highly tensioned, and even minor contact with vehicles can cause the barriers to slacken. It's expensive and time consuming to "retention" the wire, meaning many remain slack and of little use.

Wire rope safety barriers also have limited capacity to slow or absorb the energy of larger vehicles like trucks and buses when compared with, say, a concrete barrier. It's estimated that wire barriers will often become "frangible" (break into fragments) when struck by vehicles heavier than 700kg, depending of course on the speed the vehicle is travelling.  

In contrast, the strength of concrete barriers means they're not regularly slackened, knocked over or driven straight through by heavy vehicles. Concrete barriers are more expensive to install but the costly maintenance of wire rope safety barriers means they are more expensive over their life cycle. 

But, perhaps most importantly, the smooth surface created by concrete barriers is by far the safest for motorcyclists, who tend to slide along the road surface after a motorcycle accident. If the first point of impact is a smooth surface they are far less likely to be killed or seriously injured. Though, as Stanford points out, "Anything will kill you if you hit it hard enough. But having a smooth surface at least gives the rider a chance, the posts are lethal."   

When are wire rope safety barriers suitable?

"There has to be a very careful set of criteria used to determine whether wire barriers, concrete barriers or something else is installed in a particular area. At the moment wire barriers are the latest craze and the authorities have decided to stick them up everywhere, but a one-size-fits-all approach doesn’t work when it comes to road safety" Stanford says. 

"Wire barriers are quite good in certain areas, particularly where there’s room between the road shoulder and the barrier. In some areas, authorities have also started padding the vertical posts, which is sensible, though a smooth surface like a concrete barrier would be preferable."