Safer roads: How cable barriers have cut deaths on NZ highways

What makes driving safer? As holidaymakers hit the highways after another grim annual road toll, Simon Wilson reports on the evidence for what really works in the fourth of a five-part series.

OPINION: In 2005, the transport agency Waka Kotahi, then called Transit New Zealand, installed 3.5 km of cable barriers on the Kāpiti Coast highway near Wellington and lowered the speed limit to 80 km/h.

Cable barriers, also known as flexible barriers, are wires and posts installed along the middle of the road to prevent head-on collisions, and along the outer sides of the road, to stop vehicles running off and crashing.

They work like this. When a vehicle hits a cable barrier, it doesn’t spin out of control and crash. The tensioned wires and weak posts “catch” the vehicle, absorbing the energy of the impact and redirecting the vehicle back into the lane it came from.

The Kāpiti Coast highway was a treacherous piece of road, usually recording a couple of deaths a year. In the 10 years after the cable barriers went up more than 100 cars crashed into them, but no one died.

It was a revelation.

Waka Kotahi calls the system “a cost-effective infrastructure treatment that can reduce the number of people killed or seriously injured in crashes by 75 per cent”. This number refers to open-road crashes and is based on multiple studies overseas, including some in Australia.

Motorcyclists worried the wires would have a lethal “cheesecutter” effect and in 2016, then-minister of transport Simon Bridges commissioned a report on this from Waka Kotahi and the Ministry of Transport.

They advised him that the cheesecutter effect is a myth. Over the 10 years to 2015, only 3 per cent of all motorcycle deaths and serious injuries in New Zealand involved hitting any kind of median barrier. Further, in a New South Wales study that looked at 20 motorcyclist deaths after the rider had hit a barrier, only three involved cable barriers. That is, other barriers are far more likely to kill.

Cable barriers are now widely used overseas. They’re not a poor cousin of rigid concrete and “semi-rigid” steel barriers. They’re the best-available option. That’s why they’re used on some new stretches of highway and in some hotspots.

Five years ago they were installed on the north face of the Brynderwyn Hills, where travellers enter Northland. In the first year they were hit 20 times, according to Waka Kotahi executive Brett Gliddon. No one died.

As Gliddon says, that’s 20 potentially deadly crashes in a single year that everyone walked away from. The cost: just $18 million.

“Crash outcomes with flexible barrier systems,” says Austroads, the association of Australian and New Zealand transport agencies, “come the closest to eliminating the likelihood of deaths and serious injuries.”

The MoT and Waka Kotahi report to Bridges in 2016 spelled it out: “From the perspective of reducing deaths and serious injuries, the flexible wire-rope barrier is the preferred barrier type for New Zealand roads wherever possible.”

The report even asked if it would be “ethically responsible” not to install cable barriers for the benefit of “the vast majority of vehicle-based road user groups”.

So where are all the cable barriers?

How well they work isn’t the only revelation from the cable barrier story. They also prove you don’t have to build vastly expensive motorways and expressways to make the open roads safer.

And they’re not alone: features like wide shoulders, frequent passing lanes and good intersections also contribute to effective road safety.

In Sweden, they have “2+1” roads: two lanes one way, one the other, swapping regularly, with median cable barriers to keep oncoming traffic apart. It’s more expensive than occasional passing lanes but far cheaper than our expressways, and it works.

And there’s your problem. Every road with cable barriers is a road that doesn’t need to be turned into an expressway or motorway. And transport planners and politicians – not all but far too many – don’t like that.

Consider this. There are 10,000 km of roads in New Zealand identified as having “the highest concentrations of deaths and serious injuries”. They’re rated medium or high risk.

But under the National Land Transport Plan, Waka Kotahi will build only 1000 km of cable barriers on those roads, and even that will take 10 years.

The barriers cost about $150 per metre to install. All up: $150 million.

If the agency put a median cable barrier on all 10,000 km of those dangerous roads it would cost $1.5 billion. That’s the cost of just 30 km of motorway.

Take State Highway 1 from Cambridge to Tirau, a dangerous stretch of road that happens to be about 30 km long.

One way to spend $1.5 billion is to extend the Waikato Expressway to Tirau. A strong lobby wants to do that. Another is to put median cable barriers on 10,000 km of dangerous roads across the entire country, including Cambridge to Tirau.

Is that a hard call to make? Especially as Cambridge to Tirau already has some small stretches with median cable barriers. But where’s the rest?

SAFER ROADS

What makes driving safer? A Herald summer series.

Monday: More police enforcement
Tuesday: Better drivers or slower speeds?
Wednesday: The impact of safer cars
Today: Safer open roads
Friday: Safer city streets

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