Vital clues from road accidents

By SCOTT MacLEOD transport reporter

Thirty minutes after any fatal smash, when the broken bodies have been pulled from their vehicles, a team of people will turn up with a range of specialist gear.

They are members of the police crash analysis unit, and it is their job to work out what happened.

Normally there will be at least two of them. They will talk to the scene commander, possibly close the road, and quickly survey the crash site. Then they will get down to business.

Crash investigators play a big but mostly unseen role in helping to cut the road toll. Their reports on fatal and injury smashes pin down "contributing factors" such as alcohol, speed, fatigue or mechanical faults.

Ultimately, the Land Transport Safety Authority uses the police reports to decide which areas need to be targeted in advertising campaigns and vehicle checks. The reports also sway Government policy in areas as diverse as speed cameras, breath-testing, road-building and the importation of used vehicles.

One of five crash investigators in Auckland is Senior Constable Jim Downey.

He told the Herald that skid marks were a crucial clue to smashes. Police used a computer called Vericom 2000 to measure road friction. It was usually placed in a police car that was driven at 50 km/h past the crash site and then braked sharply.

The car would skid 12m to 15m before stopping, and the computer would then give a reading of the road's "stickability."

By using that data and analysing the length and arc of the smashed car's skid-marks, police could work out to within 1 km/h how fast it was travelling.

That was crucial, because speed and alcohol remained the most common factors in road smashes. A driver's alcohol level was usually easier to work out than the vehicle's speed because a blood- or breath-test could be taken. But it was fairly common for drink-drivers to run off after an accident.

One factor that sometimes made speed tricky to determine was the use of anti-skid brakes in modern cars - meaning there could be few or no marks left on the road after a smash.

However, impact-points, smash-angles and vehicle mass could still be fed into a computer to calculate speed. Until police started using the computer 18 months ago, they had to physically push the cars around to work out the impact angles.

"This new system has saved us an awful lot of time," Senior Constable Downey said.

Police are now finding that driver inattention is one of the biggest factors in accidents when there is no evidence of alcohol or speeding.

In fact, an LTSA analysis of police crash reports shows that during the 1990s speeding overtook drink-driving as the main contributor to smashes, with driver inattention now coming third.

For example, between 1995 and 1997 the number of speed-related smashes fell from 2000 each year to 1650 - a drop of 18 per cent. But drink-driving fell even further - from 780 to 595, or a drop of 24 per cent.

The authority's Craig Dowling said safety experts relied heavily on crash teams for data, although they also kept a close eye on coroners' reports.

LTSA workers used a computer to crunch the numbers in various ways so that driver details, vehicle movements, car types, roads and other factors could all be analysed for trends.

"Those patterns direct most of our road safety initiatives," Mr Dowling said. "Our guys are proud of the computer system here. We think it's the equal of anything in the world."

Herald Online feature: Cutting the road toll

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