Time Change May Put Sleepier Drivers on Road

Times Staff Writer

It’s bad enough that drivers will face another dreary, slow-and-go commute Monday. But this time they’ll be drowsier than usual, thanks to the hour of sleep they’ll lose when daylight saving time kicks in the day before.

Those who have to get to work early also will be contending with that extra hour of darkness before the sun comes up.

But does losing sleep during the transition to daylight saving time really make for more automobile collisions?


It depends on whom you ask.

Experts on traffic safety say that even if people are sleepier than usual the first day or two after the change, daylight saving time is actually a boon to safety, reducing fatalities in the evening because it’s still light outside.

But sleep specialists say grogginess from losing an hour of sleep as we “spring forward” does make it harder to pay attention on the road.

Darrel Drobnich, an expert on drowsy driving with the National Sleep Foundation, said it typically takes three to four days after the time change for our bodies to adjust fully. For many chronically sleep-deprived American adults, he said, even the loss of a small amount of sleep can affect driving.

“Losing a half-hour of sleep can be enough to make you tired,” Drobnich said. “Lose attention for two to three seconds and that’s all it takes -- especially at 65 miles per hour.”

Sleep scientists analyzing data from 21 years of car crashes concluded in 2001 that the number of fatal collisions increased slightly on the Sunday and Monday after the switch to daylight saving time. When standard time returns in the fall and clocks are turned back an hour, researchers Jason Varughese of Stanford and Richard P. Allen of Johns Hopkins wrote, there also were more accidents, possibly because people were staying out later the Saturday night before.

“The loss of one hour in the spring leads to a loss of sleep while the body’s circadian rhythm adjusts to the [time change] with a possible increase of accidents,” Varughese and Allen wrote. The effect was more pronounced the Monday after the switch, they theorized, because during the workweek drivers don’t have the option of sleeping late that many have Sundays.

In California, a rudimentary analysis of statewide crash data was mixed, but it did appear to show a small increase in collisions the Monday after the switch.

Overall collisions went up slightly in four of the six years from 1999 to 2004, as compared to the prior Monday. Accidents on the Sunday after the time change went up in just two of the six years.

Susan Ferguson, senior vice president for research at the Insurance Institute for Highway Safety, says such basic analysis of crash data misses the bigger picture, which shows that driving during daylight saving time is generally safer.

“You need to look at trends,” Ferguson said. “You can’t just look at one day here and one day there.”

In 1995, Ferguson and several colleagues published a study in the American Journal of Public Health that showed fatal accidents decreasing in the weeks after the switch to daylight saving time in the spring, and increasing after the change back to standard time in the fall.

During daylight saving time, the study showed, the extra hour of sunlight typically occurred during peak traffic periods and cut the number of fatalities even further. The biggest reduction was in the number of pedestrian deaths, because drivers were better able to see people walking in the street.

Though daylight saving time does make it darker in the morning, fewer people tend to drive that early, so there was not a corresponding increase in fatalities before dawn, the study said.

Far from viewing daylight saving time as dangerous, the study’s authors recommended switching to it year-round, a move they said would have saved more than 900 lives over the five-year period they studied.



Time to spring forward

The payoff for losing an hour of sleep Sunday is an extra hour of evening daylight over the next several months. Here’s an explanation of daylight saving time, plus some background and history.


When do clocks change?

In the U.S., daylight saving time begins the first Sunday of April (April 3 this year) and ends the last Sunday of October. Clocks change at 2 a.m. local time:

* In spring, clocks ‘spring forward’ from 2 a.m. to 3 a.m.

* In fall, clocks ‘fall back’ from 2 a.m. to 1 a.m.

Daylight time is not observed in Hawaii, American Samoa, Guam, Puerto Rico, the Virgin Islands, most of the Eastern time zone portion of Indiana and Arizona (except the Navajo Indian Reservation, which does observe daylight time).


Pros and cons

* Longer days mean fewer hours in the evening that require artificial lighting, saving about 1% in electricity costs.

* Studies have found that daylight time reduces traffic accidents and fatalities by nearly 1%.

* Farmers and others whose schedules are tied to sunrise tend to find daylight time an unnecessary inconvenience.

* People with sleep disorders may find the transition difficult.



1784: The idea is first suggested by Benjamin Franklin in an essay called ‘An Economical Project.’

1918: Daylight time is formally adopted in the U.S. It has been used in many European countries since World War I.

1942: During World War II, President Roosevelt instituted year-round daylight time, called ‘War Time.’

1966: By this time, most Americans are observing daylight time based on local laws and customs. To establish consistency, Congress passed the Uniform Time Act: daylight time would begin the last Sunday of April and end the last Sunday of October. Any state could exempt itself from daylight time by passing a state law.

1974: President Nixon signs the Emergency Daylight Saving Time Energy Conservation Act on Jan. 4, 1974. Clocks are set ahead one hour for a 15-month period ending April 27, 1975.

1986: Congress amends the law so that daylight time would begin earlier, on the first Sunday in April.



Resetting the clock during the longer days of late spring, summer and early autumn has the effect of shifting an hour of daylight from the morning to the evening.


Indiana, a special case

By state law, there are three time arrangements in the Hoosier State:

* 10 counties are in the Central Time Zone and use both Central Standard and Central Daylight Time.

* 77 counties (including the state capital, Indianapolis) are in the Eastern Time Zone and remain on standard time all year.

* Five counties are in the Eastern Time Zone but use both Eastern Standard and Eastern Daylight Time.


The astronomy of daylight

The earth’s 23.5-degree tilt causes longer days in summer and shorter days in winter the farther one moves from the equator.

In the winter, the sun’s rays hit northern latitudes more indirectly, which accounts for the shorter days. At the same time of year, it’s summer in the Southern Hemisphere.

In the summer, the sun’s rays hit northern latitudes more directly, which accounts for the longer days. At the same time of year, it’s winter in the Southern Hemisphere.


Sources:, NOAA Photo Library, The Heritage of the Great War, World Book