Driving more slowly definitely saves lives

Hank Weiss and Dorothy Begg take issue with the idea that speed limits are not to blame for accidents.

As injury prevention specialists representing a combined 50-plus years of experience in injury prevention and road safety and as leaders of the Injury Prevention Research Unit at the University of Otago, we wish to express concern at the headline (ODT, 7.1.10) that suggested that speed limits are not to blame for accidents.

Both physical laws and overwhelming real-world research evidence points to strong connections between effective efforts to lower speed and reductions in crashes, injury severity and risk of death for cyclists and pedestrians (such as the incident in the article where Claudia Petersson was severely injured crossing the road after walking the Paradise Track), and for occupants.

The reason for this is straightforward and based on well-known principles of physics.

It is because when a crash occurs, the forces (kinetic energy) released are exponentially related to the speed of a collision (for the mathematicians among readers, this is determined by the formula Ek=(1/2)mv2, where k = kinetic energy, m = mass, and v = velocity).

Because of this, there is a sensitive relationship between speed and the injury-causing potential of a crash; which means even modest speed changes can have dramatic effects.

For example, for occupants, at an impact speed of 80kmh, the risk of death is 20 times that at 30kmh (European Transport Safety Council, 1995).

For pedestrians, the risk of death is less than 5% under 30kmh but becomes almost certain over 55-60kmh (Ashton and Mackay, 1979; Anderson, McClean, Farmer et al, 1997).

Applying these principles, Western Australia safety authorities have estimated that if the vehicles involved in pedestrian injury incidents had been travelling just five kmh slower, one-third of the pedestrian deaths could have been avoided and one in 10 pedestrians would not have been hit at all (Office of Road Safety, 2009).

It is clear, then, how lower speeds would have helped Claudia Petersson on that fateful day when she was crossing the road to her car from the Paradise Track entrance in 2005 when she was struck by a utility vehicle coming around the bend.

First, she and the driver would have had more time to react to possibly avoid the collision altogether.

Second, if she was struck at lower speeds, the injuries might not have been so severe.

For these reasons, we strongly support the community and the Petersson family (ODT, 6.1.10) efforts to reduce speed limits on this road.

But speed moderation is not the only arrow in the road safety quiver.

We also agree with the DCC spokesman on the need for improved pedestrian and driver signage in this and similar areas.

Yes, signs cannot be put everywhere, but signs can and should be properly placed where obvious hazards exist.

Finally, another important design factor was not mentioned at all in the articles, and that is the design flaw, probably handed down decades ago, that requires pedestrians using the tramping track entrance to cross a dangerous roadway to get to their vehicle.

A much safer design would place the parking on the same side of the roadway as the pedestrian access.

How many other tracks in Otago have this same design flaw?Still, speed remains one of the most important road safety issues.

The slower we drive, the more time we have to react, the less chance we have of hitting something or someone, and physics says the lesser the injury and damage to things and people in and outside of the vehicle.

And while we may not have survey data on Otago citizens' attitudes right now, it has been shown from Scottish surveys that 88% prefer to drive at a speed at or below the speed limit. (Stradling, S. G., 2007).

We strongly urge the DCC in its review of speed limits to lower speeds wherever possible, in accordance with the emerging NZ Transport Agency concept of Safe Systems where speeds are based taking into account human physical and psychological vulnerability matched to the design, use and function of the road and implemented in a way that encourages compliance.

The idea is to acknowledge that people, being human, will make mistakes in judgement and that such errors, regardless whether it is the pedestrian, cyclist, motorcyclist or the driver who may be at fault, will not result in catastrophic injury or death.

We must move towards a better balance of safety, reducing health care and compensation costs, listening to local community wishes and addressing local and global environmental concerns; rather than the primacy of moving people from point A to point B as fast as possible.

Dr Hank Weiss is director and Dr Dorothy Begg transport safety co-ordinator of Otago Injury Prevention Research Unit at the University of Otago.