Experts are taking aim at police plans to target speeding drivers over summer, saying the campaign will hit "mums and dads" but miss those who cause most fatal accidents.
Police will have a reduced tolerance of 4kmh above the official speed limit over December and January. During that period last year there were 416 serious injuries on New Zealand roads, including 57 deaths.
Road safety campaigner Clive Matthew-Wilson said the campaign was aimed at "happy holiday families".
However, research had shown fatal accidents were far more often caused by substance abusers, tired drivers, highly reckless drivers, the very young and the very old.
"All five of these groups are largely immune to road safety messages because they believe they're already doing OK."
Assistant commissioner of road policing Dave Cliff said research showed focusing on a lower speeding tolerance had a major impact on all levels of road trauma.
Most drivers would heed the message to slow down and would not be ticketed, he said.
But Matthew-Wilson said about 80 per cent of fatalities occurred at speeds below the legal limit.
Massey University marketing lecturer Dr Terry Macpherson said the Government had overstated the role advertising played in lowering the road toll.
"Ads telling people not to do something generally only work if the person watching the ad is already on your side."
Criminologist Greg Newbold spoke of a man who caused the deaths of four people when he crashed while drunk and on cannabis on New Year's Eve 2001.
"I'd like to know how ticketing mothers for going 5km over the speed limit can prevent accidents like this."
Police have said previous reductions in the speeding tolerance cut road crashes by 67 per cent.
The lower drink-driving limits from December are:Related story: Drink-drive limits lowered