Slippery When Wet

by Fiona Simms

May 11, 2006

Drivers, particularly young and inexperienced motorists need to be aware of changes in our roads with winter approaching. Speed mixed with wet and oily roads can be a cocktail that P-platers and other young drivers haven’t had to deal with before.

An Office of Road Safety study of traffic related accidents and their causes, found that in the metropolitan area alone, there is an average of 22 deaths per year and 324 hospitalisations due to wet road conditions, not to mention 1038 people requiring medical attention after wet road incidences.

In rural areas, the numbers aren’t much better with 10 fatalities and 232 hospitalisations due to unfamiliarity with the wet after long dry spells.

Martin Simms, a consulting forensic and mechanical engineer said: “oil residue builds up on the roads over summer from leaking transmission and engines, which is why there is a black strip that runs down the middle of each lane. Because oil is lighter than water, the rain releases the oily matter and forms a slippery film on the road surface”.

When the first rain of the season  comes, we must be aware that the swirling, oily, rainbow patterns on the road that amused us as children can be more dangerous that we realise.

Senior Constable Kevin Donnelly from Fremantle Crash Investigations police unit said: “In the south metropolitan area we see about 250 accidents per week of all types and degrees, but the number of actual road accidents and fatalities definitely increases in the wet. Last year we had 9631 reports in just our south metro area, and they certainly come through more often when it rains. South Street is a long stretch of road and is the route of both trucks and busses, which are either slow or frequently stopping. It is important to have a safe distance behind these vehicles in the wet, accidents with large or heavy vehicles are often more serious than accidents with small cars or sedans”.

Mr Simms said: “drivers often fail to modify their dry-road driving habits. Water alone can increase stopping distance, but this is added to by the presence of oil.”

The roads can’t be blamed entirely for these skidding related accidents, speed and worn tyres are often at the root of the problem.

New tyre tread is usually 8-10mm, but as Mr Simms stated: “whilst the legal minimum tread depth of 1.5mm is adequate on dry roads in normal conditions, it is generally inadequate in the wet”.