Highly motorised countries had an average 9% reduction in fatalities despite population increases averaging 17% over the decade between 1986 and 1996   OECD countries averaged 2.3% reduction per year between 1990 and 2000 and 4.4% in 2001. 

The charts show New Zealand is consistent with these worldwide trends ⁸ .  The police slogan "The Road Toll Must Come Down" is fatuous.  The road toll is coming down anyway, and excessive and misdirected policing has no impact on it.

See charts from:  OECD International Road Traffic and Accident Database  

The following comparative charts are from Monash University

Many OECD countries have shown a very consistent exponential decay in normalised fatalities since 1970:

A smaller group of OECD countries (including New Zealand) show similar or greater exponential decay in normalised fatalities but only after around 1990:

These are the average annual reductions in fatalities per 100,000 population calculated by fitting an exponential decay curve to the IRTAD data:

This chart shows the IRTAD data for New Zealand since 1970. Major enforcement legislative changes are shown in black. Other relevant Government regulatory changes are shown in pink as is the decay curve representing a constant 4.48% annual reduction since 1990.

As with almost all countries in the above tables, the data is an excellent fit to a continuous decay curve. However in New Zealand this continuous improvement in casualties per 100,000 people began only after the country's automobile industry was normalised by the removal of barriers to imports in the late 1980s. The charts below show the reason. Prior to this economic reform, NZ had a low rate of car ownership. Casualties per car declined relatively steadily but the increasing car ownership created a flat or upward trend in casualties per population prior to 1990.

A second factor in the economic reform was the modernisation of the NZ vehicle fleet. Previously the import barriers and artificially high car prices meant that a large proportion of vehicles on NZ roads were very old. As new and recent second-hand imports came into the country the fleet was modernised and improvements in car safety design put New Zealand back on track with the international trends.

FInally, it is clear that the casualty data show the many and varied legislative enforcement interventions have had no detectable effect. The smooth improvement curve is clearly due to other factors, certainly vehicle standards, probably also highway improvements and medical care advances.

New Zealand Fails to Make a Difference

In December 2000 the New Zealand Government rolled out a major expansion of traffic enforcement resources adopting a high visibility/heavy patrolling/rigid enforcement of speed limit policy. The policy was intended to meet a goal of reducing the annual road fatalities to less than 300 by 2010. It has failed to make a difference to the international trends New Zealand has been following. For 2008 there were 365 fatalities and for 2009, 384.

These charts show the results which are consistent with the worldwide evidence that reduced speed limits are associated with increased crash rates and insignificant reduction in fatalities

The first is from the Ministry of Social Development :

These are from LTSA data available from the link at the bottom of this page:

So there is no evidence that this huge cost and imposition on the peaceful lives of ordinary New Zealanders has produced any benefit whatsoever.  Rather it has most likely caused both direct harm through increased crash rates and indirect harm by misdirecting resources of both police and taxpaying vehicle owners to counterproductive activities.