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Why use flexible road safety barriers?

Flexible road safety barriers

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 of run-off-road crashes.

Flexible road safety barriers ‘catch’ vehicles that leave their lane before they hit something less forgiving – like other vehicles or roadside hazards such as trees, poles 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.

Depending on the speed and angle of the impact a number of posts may bend over. This is how the posts are designed and does not lessen the safety benefits.

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 New Zealand roads is that they are narrow so can often be installed without significant widening of the road. They are cost effective to install and they work – results show a 70–80 percent reduction in road fatalities wherever they’re installed.

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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 effective in preventing deaths and injuries for all road users including motorcyclists.

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 the steel ropes will act like a ‘cheese cutter’ when hit by a rider. However, studies have shown this assumption is not correct.

Motorcyclists are more likely to survive an impact with a flexible road safety barrier than an impact with trees, poles or oncoming vehicles which the barrier will prevent them 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 contributed to 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 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.

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Where in New Zealand

A 3.5km long median safety 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 the flexible median safety barrier and lowering the speed limit to 80kph, there were no fatal and no major injury crashes, 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.


Centennial Highway Safe System case study(external link) (Youtube)

Media coverage

New road safety barriers save lives(external link)   - NZ Herald, 16 December 2016

The piece of metal that saves lives(external link) - NZ Herald, 15 September 2015

Down to the wire, barrier saves lives(external link) - Stuff, 4 November 2014

The line between life and death(external link)  - NZ Herald, 8 January 2012


Building more flexible barriers to save lives on our country roads(external link)   - Monash University, 6 August 2018