– What causes traffic jams?

The Japanese Mathematical Society of Traffic Flow set up this unique experiment to figure out why traffic jams appear for no apparent reason (see video). New Scientist explains:

Traffic that grinds to a halt and then restarts for no apparent reason is one of the biggest causes of frustration for drivers. Now a team of Japanese researchers has recreated the phenomenon on a test-track for the first time. The mathematical theory behind these so-called “shockwave” jams was developed more than 15 years ago using models that show jams appear from nowhere on roads carrying their maximum capacity of free-flowing traffic – typically triggered by a single driver slowing down.

After that first vehicle brakes, the driver behind must also slow, and a shockwave jam of bunching cars appears, travelling backwards through the traffic. The theory has frequently been modelled in computer simulations, and seems to fit with observations of real traffic, but has never been recreated experimentally until now.

There’s more explanation at the New Scientist web site. Read the rest of this entry »


-Was Chernobyl as tame as Andrew Bolt claims?

The West Wing on cartography and social equity

Herald Sun journalist Andrew Bolt glosses easily over the potential negative health implications of the troubled Fukushima Dai-Ichi nuclear reactor in Japan. He says too much emphasis is given to the Chernobyl disaster because, contrary to received wisdom, he maintains only 65 deaths are associated with this accident. But there’s more to it than that.

These accounts (here and here)  from Wiki indicate there are wildly varying claims about the number of deaths associated with the accident. The World Health Organisation estimated deaths at 4,000; Greenpeace at 200,000; and this Russian report, translated in 2007, says there were one million deaths, 170,000 of them in North America.

However estimates of deaths by the UN Scientific Committee on the Effects of Radiation are broadly consistent with Andrew Bolt’s claims. But what Bolt fails to mention, and the UN draws attention to, is the long run health implications of the accident.

For example, by 2005 there were 6,000 diagnosed cases of thyroid cancer among residents of Belarus, Ukraine and proximate parts of Russia, who were children at the time of the accident. According to the UN, it is most likely that a large fraction of these cancer cases are attributable to radioiodine intake (fortunately, thyroid cancer is usually treatable – the 30 year survival rate is 92% – but it’s a gruelling experience).

Now a new study has drawn attention to the cognitive risks of radiation exposure. Douglas Almond, a Columbia University Professor, wrote to the New York Times earlier this month pointing out that even low levels of radiation can have severe consequences for unborn children. He and his collaborators recently published a study of the effect of fallout from Chernobyl on Swedish children.

Sweden experienced radiation levels from Chernobyl that were so low they were considered safe. Almond’s team confirms that this presumption was mostly right. However they found that “Swedish students who were in utero during the accident experienced significantly lower cognitive functions, as reflected in performance on standardised tests in middle school, especially those tests that correspond best to IQ”. Read the rest of this entry »