Police out in force this weekend targeting drivers breaching the speed limit by even a couple of clicks but there is no conclusive evidence yet that the new lowered threshold saves lives.
A summer-long reduction in the traditional 10kmh speed tolerance to just 4kmh has started, with police citing previous success during long weekends when it has been applied and the chance to save lives over the holidays.
But an analysis of crash statistics by the Sunday Star-Times since police first started using the low tolerance three years ago shows mixed results.
When announcing the summer campaign, assistant commissioner of road policing Dave Cliff said research showed dropping the tolerance during Queen's Birthday weekends in 2010 and 2011 resulted in the number of fatal and injury crashes falling by 25 per cent compared to the previous two years.
But he chose to omit last year's data, when seven people died. Two died in 2010 and one in 2011, compared with 10 in 2009 and three in 2008. No-one died over the 2013 Queen's Birthday weekend.
Endorsing the policy, Police Minister Anne Tolley said the reduced tolerance had already proved effective, citing the example of last year's Easter road toll, when there were no deaths. She did not mention the three deaths this Easter.
Labour weekend has proved even more variable. Total crashes fell by just one in the first year the lower tolerance was applied, fell again in 2011 and then went up in 2012. Statistics for this year have not yet been released.
Over Christmas-New Year, total crashes fell in the first year of the lower tolerance, went up again in 2011, and fell again in 2012.
Overall, total injury crashes have been falling each year for the past 10 years - well before the lowered tolerance was introduced.
The Ministry of Transport attributes this to a combination of safer vehicles, improvements in the roading network, and increased enforcement.
The MOT expected the road toll to fall on average by 10 deaths per year even without additional enforcement, following a trend that has been in place since 1973 - when New Zealand posted its highest-ever road toll of 843.
While MOT data shows just 13 per cent of fatal crashes were attributable to speed* Land Transport Safety Authority spokesman Andy Knackstedt said there was "a wealth of evidence" that showed even very small reductions in speed led to reductions in fatalities and serious injuries, and that lowering the enforcement tolerance meant lower mean speeds.
Automobile Association spokesman Dylan Thomsen said police risked losing public support if they ticketed too many drivers over the summer travelling at a fraction over the limit - particularly around motorways and passing lanes.
*13 per cent of fatal crashes are attributable to speed alone. The final word of the sentence was omitted during the editing process from the original published version of this story. The sentence should have read: "Although police continue to target speeding, MOT data shows just 13 per cent of fatal crashes were attributable to speed alone. The numbers jump to over 50 per cent when alcohol and drugs are included."
- Sunday Star Times