Nearly 100 dedicated road police positions have been cut in the past five years, while the road toll rose 50 percent in the same period.
There are still more than 100 road policing vacancies despite a targeted multimillion-dollar payment in April to boost numbers, official figures released to RNZ showed.
Crashes on New Zealand roads killed 253 people in 2013 - the lowest on record since 1950 - but five years later it had risen by 49.8 percent to 379 in 2017.
During that same period the number of dedicated road police fell from 1063 to 976.
Police Association president Chris Cahill said it was impossible to say the two facts were unrelated.
"Without a doubt, there has to be some correlation... The limited or lesser amount of road policing enforcement being done will be having an effect on the road toll," Mr Cahill said.
Road policing was one victim of a resourcing shortfall which saw staffing capacity stretched, he said.
Road statistics 2013 to 2017
- Road toll rose nearly 50 percent, from 253 to 379.
- Road policing restructured at Counties-Manukau, Waitematā, Eastern, Wellington, National headquarters, Tasman, Canterbury and Southern districts. All but Waitematā district cut staff.
- The number of police patrolling roads drops 8.5 percent from 1073 to 976.
- Auckland City loses the greatest proportion of their road policing staff (61 percent), followed by Counties Manukau (30 percent), Wellington (25 percent), and Canterbury (12 percent).
- The number of road police in senior leadership positions falls 20 percent.
The toll had fallen dramatically during the previous National government's first term - from 366 in 2008 - but National Party police spokesperson Chris Bishop said it was not just about money or police numbers.
"Lots of factors go into the road toll: the quality of cars, the culture of driving, speed obviously ... so you've got to look at things in totality.
"Resources are a part of it, but there are lots of other factors as well."
Mr Bishop said road deaths per capita and per car-on-the-road were actually trending down.
However, Transport Agency figures showed that was not the case. Deaths per 100,000 people rose from 5.7 in 2013 to 7.8 in 2017. Deaths per 10,000 cars also rose from 0.8 in 2013 to 0.9 a year later, and remained steady through 2015 and 2016.
Policing decline 'a serious concern' - former road policing boss
Dave Cliff was New Zealand's assistant police commissioner in charge of road policing between 2012 and 2015. He now works with the Global Road Safety Partnership in Switzerland.
He said there was no doubt having fewer police on the roads had an impact on the road toll.
"Road policing is a critical part of the Safe System approach to road safety. If road policing is declining, that is a serious concern," he said.
"We know that the deterrence value of a police officer, the deterrence value of speed cameras, is major. And I don't think any country would want to see a decline in terms of its road policing numbers."
Other countries were way ahead of New Zealand in reducing their road toll, Mr Cliff said.
"In terms of the deaths per 100,000 population, which is the international barometer at the moment, [the leaders] are Switzerland ... which is down to two deaths per 100,000. The UK has traditionally been very good, as has the Netherlands."
101 positions vacant
In late 2016, police cut 111 road policing positions after a funding dispute with the Transport Agency.
Then-Police minister Paula Bennett made an urgent appeal for funding, prompting $10m boost to bring the numbers back up, but only 10 new officers have been hired.
There are still 101 road policing vacancies.
Police declined to be interviewed, but in a statement said maintaining order on the roads was a job for the entire force, not just road police.
"Any police officer is expected to take action if they see dangerous behaviour on our roads, they don't have to be road policing officers.
"Filling [the 101 vacancies] takes time, however it is a priority for police."
Mr Bishop maintained National should be proud of its policing record, but agreed road policing would be a concern for new minister Stuart Nash.
"Yes, I think road police would be, and should be, a priority for him."
Mr Nash said that based on the figures, the equation was simple.
"We have an increasing road toll... We have had a decrease in the number of road police staff out there, and again that is no good for anyone," he said.
"We need to have more police on the road."
Mr Nash said he was not able to command police to hire more dedicated road officers, but people would see more police on the roads as part of Labour and New Zealand First's campaign pledge to bring in an extra 1800 police by July 2021.