John Williamson: Have your say on sensible speeds for your road

A recent study by the University of Western Australia concluded that strictly enforced speed limits could be detrimental to road safety. Photo / File

ON THE ROAD

If you want to get into a lively discussion suggest that the speed limit on your local road should be reduced, because all those other drivers are causing a danger to those living on the road.

The comments range from the need to keep the productivity of the economy moving to slower vehicles cause frustration, impatience and dangerous driving behaviour; to the signs beside the road give you mixed messages; and any new speed limit won't be enforced anyway.

The level of conversation about road speed and speed limits has been elevated to a more focused and pragmatic level over the past few years. For many years the default speed limits have been 50km/h in urban areas and 100km/h in most other places with a few 70km/h zones where there was a semi-urban environment.

Effectively, in a strictly legal sense, you can drive a back country shingle road at the same speed as a four-lane highway, except that "Driving too fast for the conditions" is the fall back offence if you have a crash.

Changes to those speed limits came as a result of crash analysis studies or pressure from local communities. There was an analysis of the road which included measuring the 85th percentile of the free speed of vehicles travelling the road and then a change might be implemented through a complicated mechanism under the "Speed Limits NZ'" rule.

The experts say that the greatest determining factor of whether you walk away or are carried away from a crash, is the speed of the impact. Photo / File

During the past few years, the evolution of the Safer Journey's Strategy, new Speed Management Guidance and the Setting of Speed Limits Rule 2017, have meant that road controlling authorities have more scope to establish appropriate speed limits to match the road environment.

There are rules to follow about evidence, consultation and general agreement. The idea is to target the top 10 per cent of high risk roads and the notion of blanket speed limit reductions across multiple communities is not an option.

The cynic could rightfully claim that across the board reductions is a trade off for lack of roading development expenditure, if that was to be the approach.

Some people believe that the more you drive on a shingle road, the better you get and that enforcement on rural roads is neither possible or practicable. Photo / File

The evidence about the higher the speed, the bigger the mess is quite compelling and unequivocal. The risk of death or serious injury increases exponentially into a sigmoid curve with the impact speed.

The nature of the curve relating to pedestrians, side impact and frontal impact is subject to ongoing scientific debate but it's a fair statement that: "the greatest determining factor of whether you walk away or are carried away from a crash, is the speed of the impact."

But, the research is not all one way. Setting speed limits is one thing, enforcing them realistically is another. A recent study by the University of Western Australia concluded that strictly enforced speed limits could be detrimental to road safety.

Using a simulated driving study where participants were fined for one, six or 11km/h over a 50km/h limit, the study found that stricter enforcement reduces driver peripheral vision to detect roadside hazards, and increased stress levels, as drivers dedicated more time to monitoring speed.

Then there are those who believe that the more you drive on a shingle road, the better you get and that enforcement on rural roads is neither possible or practicable.

The established speed limit for a roading network is a legal limit. It should also be seen as a signal to drivers about the safe and appropriate maximum speed to drive the road.

Northland road controlling authorities are consulting on proposed speed limits as a network staged approach. They are establishing options, seeking and listening to feedback and establishing general agreement about how fast you should drive these networks.

A speed limit review is coming to a road near you. Have your say about sensible speeds for the roads you drive on.

• John Williamson is chairman of Roadsafe Northland and Northland Road Safety Trust, a former national councillor for NZ Automobile Association and former Whangārei District Council member.