Alcohol and drugs are a common factor in fatal road crashes, such as this one near Nelson in January.

Despite ever-harsher laws, targeted ad campaigns, and new forms of punishment, the percentage of drunk and drugged drivers involved in fatal crashes is on the rise.

While the latest New Zealand Transport Agency figures – from January 1 to June 30 – represent an incomplete picture compared with full-year figures, the 41 per cent of alcohol and/or drug-impaired drivers involved in fatal crashes in the first half of 2018 hardly paints a picture of progress.

ROSS GIBLIN/STUFF New Zealand's road toll is continuing to climb, with 2018 already the second deadliest year since 2010.

The figure is slightly up from the 39 per cent involved in fatal crashes in the first half of last year.

From 1995 to 2017, the percentage of impaired drivers involved in fatal crashes fluctuated between 15 per cent (1999) and 25 per cent (2010).

MARION VAN DIJK/STUFF National road policing manager Superintendent Steve Greally says the message around drink-driving is still not getting through. (File photo)

National road policing manager Superintendent Steve Greally said he was as baffled as anyone as to why the message was not getting through.

"We don't know why some drivers still choose to take risks and don't listen," he said.

"Drivers who get behind the wheel while under the influence of drugs or alcohol are not only putting themselves, but also all road users, at risk."





Police will be out in force again over the holiday period, but there will inevitably be drink-drivers on the roads, and crashes to deal with.

STUFF Alcohol interlocks require a person to pass a breathalyser test in order to start their car's ignition. (File photo)

The legal adult alcohol limit has dropped several times since it was first introduced in 1969, and now stands at 50 milligrams (mg) per 100 millilitres (ml) of blood, or 250 micrograms (mcg) per litre of breath.

For drivers under 20, there is a zero alcohol limit.

Harsher penalties have also been introduced for repeat drink-driving offenders, and in 2009 a drug driving offence was introduced.

Three years later, the interlock system was established for repeat and serious first-time offenders. Earlier this year, that sentence - which requires a driver to clear a breathalyser test to start a car's ignition - was made a mandatory punishment for those offenders.

Automobile Association (AA) road safety spokesman Dylan Thomsen said the mandatory interlock sentence could have the biggest impact yet on recidivist drink-drivers.

Up until July, when the law was changed, only two or three per cent of offenders eligible for an interlock sentence had the punishment imposed.

It's not clear why that was the case, but Thomsen said because the sentence was not mandatory, it was often strongly opposed by defence lawyers.

MIKE CLARE/SUPPLIED Automobile Association road safety spokesman Dylan Thomsen says mandatory interlock sentences for repeat and serious drink-drivers could make our roads much safer. (File photo)

"There are about 300 interlock sentences handed out each year, but that should be about 5000 each year," Thomsen said.

Looking at the numbers, it was clear the mandatory sentence could lead to a "huge reduction" in drink-driving.

In 2016, the 353 interlock devices handed out prevented more than 2100 instances of drink-driving.

While the laws are the toughest they have been, some say many of the road deaths could be wiped out completely if we bit the bullet and got tougher.

"If I told you we're going to have a zero-alcohol limit, that would have an incredible reduction in harm, but people won't wear that," said transport researcher Samuel Charlton, an associate professor at the University of Waikato.

"They just won't. Because you have other things to consider such as mobility in remote communities."

DOMINICO ZAPATA/STUFF University of Waikato associate professor Samuel Charlton says a zero-alcohol limit would not fly in New Zealand.

Road safety charity Brake said recently that repeat drink-drivers should be permanently banned from using the country's roads, but the idea was shut down by Associate Transport Minister Julie Anne Genter, who said that would be a "serious step to take".

The charity also said New Zealand should have an "effective" zero-tolerance drink-driving limit (20mg per 100ml), higher fines and demerit points, and more random breath testing.

Meanwhile, Wairarapa MP Alistair Scott's member's bill to introduce roadside saliva-based drug tests, which is currently before Parliament, faced a tough time at its first reading in September.

Transport Minister Phil Twyford said drugged drivers were a serious problem, but Scott's bill had flaws which made it impractical to implement.

"The tests are slow, they are expensive at $45 a test, they identify only three types of drugs [cannabis, MDMA and methamphetamine], and this is the critical point: they only detect the presence of the drug; they have nothing to say about impairment."