Tuesday, November 29, 2011

New Study Shows No Link Between Road Traffic Collisions & Daylight Saving Time

People who follow the news know that every year, around this time, there seem to be an increase in trusted information sources warning us about bicycles and pedestrians colliding with cars, and the correlation with Daylight Savings Time. Some of these vehicle collisions are fatal, and we remember when someone dies. Invariably the reports quote police officers and traffic safety officials attributing said automobile collisions to the twice-a-year annual changing of the clocks, the explanation being that either the onset of darkness is sooner and people are in a rush to get home, or there's not enough light early in the morning when people are in a rush to get to work, or people have to wake up earlier than they are used to, and this disruption in the body's Circadian rhythm means people are less aware at the wheel. In many cases, you add on the idea that some motorists have problems adjusting their eyes to the new light level, or the sun may be in their eyes, or it's too dark, and one can readily see why accidents might abound around the changing of the clock. The idea then that there is a correlation between Daylight Saving Time and an increased rate of accidents sounds plausible, even somewhat convincing. But what if there is no increase in traffic accidents around Daylight Savings Time? In order to avoid confirmation bias (the notion that "people see what they want to see", in that it is a particular human weakness that we all remember the purported evidence that supports an idea we want to believe, and we discard any suspect evidence that threatens that belief), one should approach an answer to this question using the power of science.

In the past, there've been studies to support this claim. However, the latest study, culled from Wikipedia, seems to show, at the very least, the jury is still out, and that there may even be no connection:
According to earlier studies, this change in time-schedule leads to sleep disruption and fragmentation of the circadian rhythm. Since sleep deprivation decreases motivation, attention, and alertness, transitions into and out of daylight saving time may increase the amount of accidents during the following days after the transition. We studied the amount of road traffic accidents one week before and one week after transitions into and out of daylight saving time during years from 1981 to 2006. Our results demonstrated that transitions into and out of daylight saving time did not increase the number of traffic road accidents.
2010 Jun 27.
Daylight saving time transitions and road traffic accidents.
Lahti T, Nysten E, Haukka J, Sulander P, Partonen T.


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