Ask Phoebe: Wire ropes are safer

The barrier stretches for 3.4km. Photo / NZTA

I would like to know how the NZTA can justify installing wire rope barriers on our main roads. Have you seen what happens to a motorcyclist should they come off their bike and hit one of these?

If you're not decapitated and killed outright, the injuries are horrific and usually limbs are lost.

This type of barrier should be banned, so I would appreciate a response from NZTA as to why it has zero consideration for the safety of motorcyclists. Greg Ewen, Auckland.

The Transport Agency was happy to provide the following:

"The main purpose of wire rope safety barriers is to stop traffic leaving the road and colliding with solid objects such as other vehicles, trees and poles.

Studies show the fear that the steel ropes have a cheese-cutter effect is unfounded, and that wire rope barriers are more forgiving than traditional steel barriers with a 70-80 per cent reduction in road deaths.

A study of New Zealand motorcycle barrier crash data from January 2001 to July 2013 shows that of the 20 motorcycle fatalities that followed a collision with a barrier, 13 were from W-beam and three from wire rope. (A W-beam is a semi-rigid steel guard rail with a cross-section in the shape of a rounded W.)

In this same period there were 97 deaths from collisions with posts, 70 from hitting traffic signs and 93 from hitting unprotected trees.

Of the barrier collisions, wire rope safety barriers have around half the fatality rate of W-beam ones and concrete barriers are the most dangerous of all to motorcyclists.

Wire rope barriers 'catch' vehicles that leave the road. When a vehicle hits the wire rope barrier the cables flex, slowing the vehicle and pushing it back into its lane. The system absorbs impact energy, reducing the force on the passengers which means fewer and less severe injuries.

They are also designed so no part of them can penetrate the passenger compartment of cars."

How long is the Wynyard Quarter tramway likely to be out of action? Graham Bush, Parnell.

The aucklandtram.co.nz website says the tramway will not operate until late November because of road redevelopment in Wynyard Quarter.

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