Simple driver mistakes are behind about half of Kiwi road deaths, NZTA safety and environment director Harry Wilson said (file photo).

Dropping a hot pie in your lap while driving could be the difference between life and death, a road safety leader says.

Half of the deaths on Kiwi roads are because an ordinary driver made a simple mistake, according to NZ Transport Agency safety and environment director Harry Wilson.

Getting old cars off the road is also as critical as spending on roads and roadsides, he told Hamilton City councillors on this week.

NZTA "Chasing black spots is like chasing lightning, because you never know where it's going to happen," NZTA safety and environment director Harry Wilson said (file photo).

"People often focus on the cause of crashes but what we're trying to do is make sure that when crashes do happen, people don't die as a result. People will make mistakes," he said.

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Reading crash analysis reports has shown Wilson the cause can be something as bizarre as a dropped hot pie.

"That action can be the difference between life and death, simply because our roads are just not forgiving," he said.

"Chasing black spots is like chasing lightning, because you never know where it's going to happen."

Every week, seven people die and 54 are seriously injured, Wilson said - and our road toll figures are climbing.

There were 380 deaths in 2017, Wilson said, and the toll is heading towards more than 400 this year.

Hamilton City Council has adopted a Vision Zero policy - aiming for no road deaths in the city - but that's not yet reality, Councillor Dave Macpherson said.

"[W]e have got no speed limit above 80kmh right now. We're the first to bring in a 40kmh outside schools and 30kmh in some commercial areas and we have still got five deaths."

"We clearly need to do something different, and more."

Now's the time to make a difference, Wilson said, as the Government's recent $4.3b investment in road safety is New Zealand's biggest ever.

Policing numbers are up, allowing for more of a presence, he said, and NZTA is using a tool to identify spots where safety dollars could make the biggest difference.

Speed is the closest thing to a silver bullet, but people value time and generally aren't keen on lowering limits.

Getting old and ageing cars off the roads is critical to improving road safety, he said.

"Fifty per cent of the deaths and serious injuries in the past five years are in cars older than 15 years," he said.

"Twenty-six per cent of deaths and serious injuries are our youngest drivers - 16 to 24. Perfect storm: we're putting our youngest, most vulnerable people in the worst cars on our roads."

The average age of a car on Kiwi roads is about fourteen years old, he said.

So NZTA has suggested the Ministry of Transport stop cars with the lowest safety ratings coming into the market.

However, there's an environmental flipside - many of the cars rated five stars for safety are among the worst emitters.