Quoted message said:I went a bit sideways this morning on roads covered in rubber particles and diesel, nicely
lubricated with water.
snippity...
You may be interested in the following...
<http://www.newscientist.com/news/news.jsp?id=ns99994148>
"Downpour after drought raises road deaths
19:00 10 September 03
Rainy weather influences road deaths in a far more complicated way than previously thought. Rain
does not increase the number of deaths in crashes, provided it rained the previous day. But a heavy
shower after a dry spell causes a lethal surge in accidents.
Daniel Eisenberg of the University of California, Berkeley, stumbled across the link while studying
the dangers of driving under the influence of drugs. He knew that there are more accidents on rainy
days and wanted to show that this factor was not influencing his results.
But when Eisenberg calculated the annual and monthly figures for rainfall taken from the US Weather
Service's 20,000 weather stations, and compared it with nearly 430,000 fatal crashes between 1975
and 2000, he found that the number of deaths fell in rainy months.
It was only when he looked at the daily figures that he found the expected result - a 1.2 per cent
increase in the rate of fatal crashes with every centimetre of rain that falls.
Engine oil and grease
Eisenberg says the longer the dry period before it rains, the higher the number of deaths (see
graph), so a dry month with a downpour can have more deaths than one with incessant drizzle.
He found that the combination of a shower after a 21-day drought increased the number of fatalities
nearly threefold. "I think my study is the first with large-scale data to show the magnitude of the
effect," he says. The work will appear in Accident Prevention & Analysis.
Eisenberg suggests that during a drought, engine oil and grease build up so that when it rains the
oil and water mix turns the road into a skidpan. And people are also not as prepared for these
conditions after a long dry spell, he says.
Adrian Runacres, a forensic accident meteorologist at the UK's Transport Research Laboratory at
Crowthorne, says that tests in the UK have confirmed that the build-up of dust and rubber from tyres
can form a greasy film when it rains. "Also the crud that builds up blocks drainage paths between
the chips on the surface of the road," he says.
But Runacres says that the most important factor is probably motorists driving in heavy rain as
though it were still dry, and tailgating other vehicles. Eisenberg says that highway authorities
should warn motorists of the added danger when it rains after a drought.
Mick Hamer"
Cheers, helen s
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