Daylights Savings Time & Fatal Car Accidents

This weekend was daylights savings time, the one everyone dreads because you lose an hour of sleep. Sometimes, daylights savings time comes as a surprise to people who forgot about it or who did not realize it was coming.

Some people may know it is coming and adjust their clocks appropriately, but still wake up late because their bodies have yet to adjust. One potential risks of sleep disruption from spring daylights savings time is fatal car accidents. In the fall, you gain the much beloved one extra hour of sleep. There is some evidence for increased and decreased numbers of car accidents after fall daylights savings time. Increased car accidents after fall daylights savings time may be due to staying up longer than usual. Decreased car accidents after fall daylights savings time may be due to some people sleeping an extra hour that night.

An interesting study was performed in 2001 to examine the association between daylights savings time and fatal car accidents in more detail. The researchers examined data from 21 years of United States' fatal automobile accidents. The average number of accidents on the days at the time of daylights saving time shifts (Saturday, Sunday and Monday) was compared to the average of accidents on the matching day of the weeks before and after the shift. This was repeated for each daylights saving time shift.

The results of the study showed that there was a significant increase in accidents for the Monday immediately following the spring shift to daylights savings time. There was also a significant increase in number of accidents on the Sunday of the fall shift from daylights savings time. No significant changes were observed for the other days.

The authors concluded that sleep deprivation on the Monday following a shift to spring daylights savings time results in a small increase in fatal accidents. For fall daylights savings time, the authors concluded that the behavioral changes associated with anticipating the longer day on Sunday led to an increased number of accidents. This suggested an increase in late night (early Sunday morning) driving when traffic related fatalities are high possibly related to alcohol consumption and driving while sleepy.

The authors recommended that public health educators should probably consider issuing warnings both about the effects of sleep loss in the spring shift and possible behaviors such as staying out later, particularly when consuming alcohol in the fall shift. The authors concluded that physical and behavioral responses of the body to forced circadian rhythm changes (the body’s biological clock) due to daylights savings changes are important factors for sleep clinicians to be aware of.

Suggested reading: Daylight Savings Time Change May Increase Heart Attack Risk.

Reference: Varughese,J., Allen, R. (2001). Fatal accidents following changes in daylight savings time: the American experience. Sleep Med., 2(1):31-36.