Should NZ's highways have median barriers?

Wednesday's horror crash in south Taranaki has sparked renewed calls for median barriers on all our state highways.

The death toll from the accident, a head-on crash, rose to seven on Thursday morning after an eight-year-old who survived the initial impact succumbed to her injuries.

Her mother remains in hospital with life-threatening injuries.

"Six people are dead because a simple barrier was missing off that road," said road safety campaigner Clive Matthew-Wilson, editor of the Dog and Lemon Guide car review site.

"That's the simple fact. If the Government is serious about lowering the road toll, the highest priority must be given to improving the safety of our third-world roads."

Last year the International Transport Forum, of which New Zealand is a member, recommended all roads without median barriers have a speed limit of no more than 70km/h.

A report presented to then Minister of Transport Simon Bridges in 2016 said head-on collisions resulted in more deaths and injuries on busy roads than any other cause. It recommended installing flexible wire barriers, saying not only are they more cost-effective than solid barriers, but also safer.

The New Zealand Transport Agency (NZTA) says median barriers save lives. One stretch of highway north of Wellington saw an average of two deaths a year before having a median barrier installed in 2005 - since then, there have been none.

Mr Matthew-Wilson says the previous National-led Government spent its transport budget on "a few grand highway schemes" with little attention paid to safety.

"The new Government has given the New Zealand Transport Agency billions to improve our roading system. It's now up to the NZTA to prioritise spending on safety."

Former Reserve Bank Governor Don Brash told The AM Show on Thursday installing median barriers along New Zealand's state highway network would bankrupt the country - but that wouldn't be the only problem.

"There are so few passing lanes on New Zealand roads. It's okay on a motorway, no problem, no trouble at all. But on most roads you can go 30km, 40km, 50km with no passing lanes.

"If you put a median barrier, you can't get past some idiot driving at 70km/h in a 100km/h area."

He said slow drivers were "idiots" just like those who drive too fast.

"Those people build up traffic behind them, people get impatient and do stupid things."