So the traffic cops are extending their 4km-only tolerance limit until the end of the month and are looking at making it permanent. This has a feeling of pre-concieved inevitability about it. Although Acting Superintendent Rob Morgan assures us that the permanent adoption “will really be an evidence-based decision”, we all know that this is complete nonsense. There is absolutely no evidence that a reduced tolerance limit will do anything except increase police ticket revenue.
Speed limit enforcement at the margin makes little or no difference to the accident rate”
Let’s face it, whether a driver is doing 104 or 110 kph will make no real difference to accident statistics. While there is good evidence in controlled accident situations (with crash test dummies) that increased speed increases the risk of fatality, there is no reliable evidence that this is true on the open road. Empirical tests such as these are done at relatively low speeds using a test bed and a solid wall. The results are then extrapolated to high speeds, an extrapolation that is not necessarily valid, given that there are a great many other factors at play in a real traffic accident.
There is also some epidemiological evidence that increasing road speed limits increases fatalities. The repeal of the national road speed limits in the US allowed states to increase limits as they saw fit. The resulting increases did see a rise in road fatalities with a 4% average increase in speed purported to produce as much as an 17% rise in fatalities. However, most of this fatality data does not take into account traffic volume. When traffic volume increases are factored in a 10mph increase in speed limits may produce a 1.3% increase in fatalities. Not insignificant, but small potatoes compared to the enormous gains made through better, safe vehicles and roads.
I am not arguing here that speeding does not cause an increase in accident fatalities, but that speed limit enforcement at the margin makes little or no difference to the accident rate. Where speed is a significant factor in an accident, it is almost certainly excessive for the conditions. I strongly suspect that the accident rate (and, probably the fatality rate) of a late-model BMW cruising at 120kph down the (very straight) N1 freeway south of Auckland is going to be much lower that the accident rate of the jalopy with marginal tyres and shocks trying to navigate the Coromandel at the posted speed limit. Similarly, the logging truck doing 95Kph between Tokoroa and Taupo is considerably more dangerous than the MacDoctor doing 110 in his 4-year-old Hyundai Sonata on the same road. Of course the idiot doing 140Kph on that road would be more dangerous than both of us, regardless of his vehicle.
I would submit that it is not particularly useful policing speed limits, in road safety terms, when it is clear that our police ignore most careless driving incidents in favour of writing out speeding tickets. From a policing point of view speeding tickets are a whole lot less paperwork than dangerous driving tickets. Most speeders pay their fine and the case is closed. Some go to court but usually the cop in question just has to provide the written proof that the camera was calibrated and that the vehicle was properly identified. Dangerous driving, however, carries stiffer penalties and often requires the personal presence in court of the policeman who wrote the ticket. It is small wonder than, that the police prefer the simplicity of the speeding ticket, despite the fact that it contributes little to road safety.
This preoccupation with speed may well be a contributor to the reputation of Kiwis for aggressive, discourteous driving. After all, it is very rare to see anyone being pulled over for changing lanes dangerously on the freeway or even overtaking on a corner or blind rise. In fact, I cannot recall seeing anyone being issued a ticket in this country for anything other than speeding, parking or, that other favourite revenue-gathering exercise, failing to come to a complete stop at a stop sign. Anecdotally, a friend of a friend once told me they were ticketed for running a red traffic light – the only ticket I can recall ever hearing about that had something to do with genuinely dangerous driving.
If the police really wish to make further inroads on road safety, they need to stop mucking around at the margins of the speed limit and determinedly go after those few drivers who drive in a genuinely careless and dangerous manner.