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Why use flexible road safety barriers?What are they?
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We use flexible road safety barriers down the middle of a road to prevent head-on collisions or along the edge of the road to reduce the consequences run-off-road crashes.
FlexibleWire 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, or rolling.
Wire rope safety barriers differ in that they‘catch’ vehicles that accidentally leave their lanethe road before they hit something less forgiving - like other vehicles or roadside hazards such as trees, poles– when a vehicle hits the wire rope safety barrier, the cables flex, slowing down the vehicle and ditches.
When a vehicle hits these barriers the high-tension wire cables flex, slowing down the vehicle and redirecting it away from the hazard. This flexibility means that the barrier absorbs impact energy, reducing the force on the people in the vehicles, resulting in less severe injuries than other safety barrier systems and from collisions with roadside hazards or other vehicles.
redirecting it away from the hazard. Depending on the speed and angle of the impact a number of posts may bendbe bent over. This is how the posts
This flexibility means that the system absorbs impact energy, reducing the force on the people in the vehicle, which means less severe injuries than other safety barrier systems and from collisions with roadside hazards.
They are designed and doesso that parts of them do not lessenpenetrate the safety benefits.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.
Flexible road safety barriers are designed so they should not penetrate the passenger compartment of a vehicle, and the vehicle remains upright during and after a collision. They are also designed so that after impact the vehicle should not be deflected into an adjacent traffic lane.
What makes them ideally suited to many NZNew Zealand roads is that they are narrow so can often be installed without significant widening ofsignificantly having to widen the road. Theyroad, they are cost effective to install and they work – results show a 70-80 percent70-80% reduction in road fatalities wherever they’re installed.located!
MotorcyclistsMotorbikes
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 flexible safety barriers are highly effectiveeffective, in preventing deaths and injuries for all types of road users including motorcyclists.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. Motorcyclists have been opposed to flexible road safety barriers because they think
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, assuming the steel ropes act as a ‘cheese cutter’ when hit by the rider. However, studies have shown this assumption is unfounded.
In fact, the steel ropes will act likeevidence shows the opposite - installing roadside and median barriers – particularly wire-rope barriers - has a ‘cheese cutter’ when hit by a rider. However, studies have shown this assumptionbeneficial effect of around 50% in terms of reducing motorcycle casualties. This is not correct.
Motorcyclistsbecause motorcyclists are more likely to survive an impact with a flexible road safetyroadside or median wire rope barrier than an impact with the trees, poles or oncoming vehicles which the barrierbarriers will prevent them from striking in a crash.
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. A study of the NZ motorcycle-barrier crash data from January 2001 to July 2013 shows of 20 motorcycle fatalities sustained as a result of riders hitting a roadside or median barrier, just 3 involved wire rope barriers, while 13 involved traditional steel ‘W’ beam barriers and 4 other barrier types. Over the same time period there were 97 motorcyclist fatalities from collisions with posts or poles, 70 from hitting traffic signs and 93 from crashing into unprotected trees.
A study of the NZ motorcycle-barrier crash data from January 2001 to July 2013 shows of 20 motorcycle fatalities sustained as a result of riders hitting a roadside or median barrier, just 3 involved flexible safety (wire rope) barriers, while 13 involved traditional steel ‘W’ beam barriers and 4 other barrier types. Over the same time period there were 97 motorcyclist fatalities from collisions with posts or poles, 70 from hitting traffic signs and 93 from crashing into unprotected trees.
For more details on the subject:
Where in NZ
A 3.5km long3.5km-long wire rope median safety barrier wasbarrier 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 the flexiblea wire rope median safety barrier and barrier and lowering the speed limit to 80kph, there were no fatal and no major injury crashes,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
Canterbury / Marlborough travel map
