What are they?
Wire rope safety barriers are safety barriers built from steel wire ropes mounted on weak posts. Like all other road safety barriers their main purpose is to stop traffic leaving the road and colliding with solid objects such as other vehicles, trees, poles, etc.
Wire rope safety barriers differ in that they ‘catch’ vehicles that accidentally leave the road before they hit something less forgiving – when a vehicle hits the wire rope safety barrier, the cables flex, slowing the vehicle and pushing it back into its lane. Depending on the speed and angle of the impact a number of posts may be bent over.
This flexibility means that the system absorbs impact energy, reducing the force on the people in the vehicle, which means fewer and less severe injuries.
They are designed so that no part of them can penetrate the passenger compartment of a vehicle, and so that the vehicle remains upright during and after a collision. They are also designed so that after impact, the vehicle has not been deflected into an adjacent traffic lane.
They are particularly effective when used as median barriers, as cross-median crashes can be very severe. They are also more forgiving than traditional concrete or steel barriers.
What makes them ideally suited to many New Zealand roads is that they are narrow so can be installed without significantly having to widen the road, they are cost effective to install and they work – results show a 70-80% reduction in road fatalities wherever they’re located!
Motorbikes
Motorcyclists don’t have the same protection in a crash as the occupants of vehicles, and special consideration needs to be given for how to keep them safe. Roadside and median barriers are highly effective, in preventing deaths and injuries for all types of road users.
The Safe System approach to road safety holds that while mistakes are inevitable, deaths and serious injuries are not. The Transport Agency is investing in improved roads and roadsides that are increasingly safer for motorcyclists when they or other road users make mistakes.
It’s important to ensure that the technology we use to help prevent deaths and serious injuries for those in cars and trucks does not increase risks for motorcyclists. We look to do this by considering the most appropriate technology for each application.
Motorcyclists have been opposed to wire rope safety barriers, assumingfearing the steel ropes act as a ‘cheese cutter’ when hit by the rider. However, studies have shown this assumptionfear is unfounded.
In fact, the evidence shows the opposite - installing roadside and median barriers – particularly wire-rope barriers -The University of New South Wales has a beneficial effectundertaken an in-depth analysis of around 50% in terms of reducing motorcycle casualties. This is because motorcyclists are more likely to survive an impact with aimpacts into roadside or median wire rope barrier than an impact with the trees, poles or oncoming vehicles which the barriers will prevent them from striking in both New Zealand and Australia. The data shows that barriers of any kind were a crash. factor a very small percentage of motorcycle fatalities.
A study of NZ motorcycle-barrier crash data from January 2001 to July 2013 2013 shows of the 20 motorcycle fatalities sustained as a result of ridersfollowing hitting a roadside or median barrier, just13 were from W-beam and 3 involvedfrom wire rope barriers, while 13 involved traditional steel ‘W’ beam barriers and 4 other barrier types. Over the samerope. It is worth noting that in this time period there were 97 motorcyclist fatalities from collisionscollision with posts or poles, 70 from hitting a traffic signssign and 93 from crashing into unprotected trees. The University of New South Wales has undertaken an in-depth analysis of motorcycle impacts into roadside barriers in both New Zealand and Australia. The data shows that barriers of any kind were a factor a very small percentage of motorcycle fatalities.
Of the barrier collisions, the results show that wire rope safety barriers have around half the fatality rate of W-beam barriers and that concrete barriers are the most dangerous of all to motorcyclists.
For more details on the subject:
- Motorcycle Safety and Roadside Barriers - Study presentation
- Motorcycle-Barrier Impacts - Study reports
Where in NZ
A 3.5km-long wire rope median barrier was installed on SH1 Centennial Highway, just north of Wellington, in 2005. This was a particularly treacherous piece of road – in the 4 years to 2000 it recorded 8 fatalities, 2 serious injuries and 7 minor accidents. Between 2001-2004, the passing lanes were removed and road markings, reflectors and signs were increased yet it still saw 4 fatalities, 2 serious injuries and 2 minor injury accidents.
In the four years from 2005 to 2009, following the installation of a wire rope median barrier and lowering the speed limit to 80kph, there were no fatal and no major injury accidents, and just 3 minor injuries recorded.
Between 2005 and October 2015, the Centennial Highway barrier has been hit over 100 times without a single death.
The success of wire rope safety barriers in preventing death and serious injury will see more installed at high-crash locations throughout the country.
Useful videos
Centennial Highway Safe System Case Study
Media Coverage
The piece of metal that saves lives
Down to the wire, barrier saves lives
The line between life and death