-----Original Message-----
From: Alan Wilkinson
Sent: Monday, 8 November 2004 2:05 p.m.
Subject: RE: FW: Increasing traffic injuries
Hon Ruth Dyson
Minister for ACC
Copied to: Rt Hon Helen Clark, Prime-Minister.
Dear Ms Dyson
Thank you for your letter of 4 November 2004 responding to concerns over sharply rising motor vehicle injury accident trends since 2000.
Unfortunately the analysis provided to you by ACC is quite untenable for the following simple reasons.
1. The upward ACC injury trend data since 2000 is exactly confirmed by the police/LTSA traffic injury data which come from a completely independent source. There can be no question it is real and not an artifact of ACC legislative changes.
2. The increase in injuries on both data sources far exceeds the increases in vehicle travel or population over the period. For instance, had the trend prior to 2000 continued for weekly compensation injury claims these would have totalled about 1000 for the year to June 2004. The actual number was 3442, greater by a factor of 3.4. The population increase factor of 1.034 and the vehicle travel increase factor of 1.087 are completely negligible in comparison. (Moreover, the period 1994-2000 also experienced growth, yet the annual injuries were declining strongly and very consistently despite that growth.)
3. If the upward trend had begun significantly in 1999 it would have showed in the data for the year ended June 2000. It doesn't - that result is well within the normal deviation around the downward trend line for the seven years ended June 1994 thru 2000. It is crystal clear that the year ended June 2001 marks the start of a sharp upward movement. Monthly fluctuations are much greater than annual ones and cannot be taken as representative of significant changes in trends unless confirmed over much longer periods. Unfortunately, LTSA and police representatives persistently ignore this fact and hail with a big fanfare each favourable fluctuation while ignoring the next month's reversal.
4. If true (and LTSA-sourced causal factor data must be taken with a large grain of salt) that the alcohol-related crashes have reduced from 18% in 1999 to 13.2% in 2004, this only increases the magnitude of the failure of the "speed kills" programme, since despite this reduction, the overall injury trend has risen so greatly in that period.
Good intentions are insufficient. The ACC must be objective and honest about results. It doesn't matter what people believe causes accidents. What matters is what actually does cause them.
Recent detailed and extensive academic US traffic accident research I have examined fails to uphold any clear relationship between speed and crash frequency. For example, a comparison of crash frequencies on multi-lane highways failed to find any difference between fast and slow lanes. A comparison of male and female drivers found that on average males prefered to drive 7 mph faster than females. However, males and females had similar frequency of crashes per distance driven. Other studies failed to find any relationship between average speed immediately before the crash and the likelihood of a crash. Studies have also failed to confirm any consistent relationship between speed variations and crash likelihood.
In 1999, the New Zealand Midland police district hidden camera trial also failed to reduce fatalities and increased injuries despite reducing average speeds significantly. It is clear that in New Zealand since 2000 lower average speeds have failed to reduce fatalities compared with pre-existing trends and are now associated with sharply increased injuries.
I believe the rigid enforcement of speed limits has failed as an accident prevention measure for the following reasons:
Firstly, death and injury statistics trend differently and most likely depend on different factors/populations. Deaths are a very small subset of crashes and result often from very gross failures - falling asleep, intoxication, failure to slow at an intersection, head-on overtaking, falling off a hill or into a river. Most of these are unlikely to be sensitive to normal variations in speed.
Secondly, people prefer to travel at different speeds. Typically men driver faster than women yet have about the same rate of accidents or fewer per distance travelled. There are also marked variations between preferred speeds of drivers of different kinds of vehicles, drivers from different income categories and from different urban/rural environments.
I conclude that people are generally very good at judging their own risk and adjusting their driving to that. (I think research should focus on why they sometimes make errors.) Rigid enforcement of speed limits likely has the following detrimental effects:
a) Overtaking is much less efficient and less safe because it takes longer to pass slowly within the enforced speed limit and traffic bunches up behind slow vehicles.
b) Faster drivers become frustrated/impatient/bored/inattentive.
c) Slower drivers feel pressured to drive at the speed limit and are focussing on the vehicles behind instead of the road ahead.
d) All drivers try to make up time by maintaining the speed limit even on difficult curves/roadways/conditions because they cannot go faster on safe segments.
e) Drivers spend significant distraction time and focus watching their speed and looking for patrol cars and speed cameras.
The safest conditions may actually be relatively low speed limits enforced sensibly (ie only clearly dangerous/foolish infringements prosecuted). This would allow slow drivers to drive within the speed limit and within their own preferences without feeling additional pressure and would allow faster drivers to pass them in the most safe way.
Most of the traffic injury research suffers from the statistical "ecological fallacy" of assuming individual attributes can be deduced from average measurements. Just as drivers are not statistically 50% female/male, the average actually conceals quite different sub-populations which have different needs and forcing everyone to the average can be sub-optimal for almost everyone.
Whatever the reasons, it is clear that the "speed kills" policy has failed disastrously. Injuries and ACC costs are increasing. Continuing with failed policies is not an option.
The facts seem to be quite clear. Please advise whether ACC has any sound basis to defend their analysis as per my points 1-4 above. If not, the Government must act to remedy these alarming and costly injury trends. Please advise your intentions.
Yours sincerely
Alan Wilkinson
