Since March 13, 2022, which marked the beginning of daylight saving time (DST) for most states in the U.S., we have been bombarded with articles on its history, dangers, and advantages, along with news of the unanimous passage of the Sunshine Protection Act in the Senate. The legislation would make daylight saving time permanent in 2023.

Alternatively, the American Academy of Sleep Medicine (AASM) and more than 20 medical, civic, and professional organizations have endorsed a return to Permanent Standard Time, rather than adopting permanent DST.

For 100 years, there have been arguments for and against the practice of “springing forward” and “falling back” one hour. The Center was curious to see what kind of science can be used to inform the debate. It turns out there is quite a bit of research, although the field appears to lack strong systematic reviews to determine its quality.

Energy Savings

Does daylight saving time save energy? One study took advantage of a natural experiment in Indiana that looked at 7 million observations of household data over a period of three years:

“Our main finding is that—contrary to the policy’s intent—DST increases residential electricity demand. Estimates of the overall increase are approximately 1 percent, but we find that the effect is not constant throughout the DST period. DST causes the greatest increase in electricity consumption in the fall, when estimates range between 2 and 4 percent. These findings are consistent with simulation results that point to a tradeoff between reducing demand for lighting and increasing demand for heating and cooling. We estimate a cost of increased electricity bills to Indiana households of $9 million per year. We also estimate social costs of increased pollution emissions that range from $1.7 to $5.5 million per year.”

A Department of Energy report stated the impact of DST, which had been extended across the U.S. in 2005, was a savings of 0.03 percent of electricity consumption over the year 2007. This is roughly 0.02 percent of national primary energy consumption. The report also said that changes in national traffic volume and motor gasoline consumption for passenger vehicles in 2007 were not statistically significant and could not be attributed to Extended Daylight Saving Time.

Finally, a 2018 meta-analysis of 44 studies of energy savings found modest energy savings of 0.34 percent on the days that DST was in effect. The analysis determined the studies were not affected by publication bias, but results varied based on the data and methodologies applied.

Traffic Crashes

A 1996 Canadian studyfound “the spring shift to daylight savings time, and the concomitant loss of one hour of sleep, resulted in an average increase in traffic accidents of approximately 8 percent, whereas the fall shift resulted in a decrease inaccidents of approximately the same magnitude immediately after the time shift.”[1]

A U.S. study in Sleep Medicine found “the sleep deprivation on the Monday following shift to DST in the spring results in a small increase in fatal accidents.”[2]

A 2020 review in Current Biology found evidence for increased motor vehicle accidents (MVA) due to sleep deprivation and changing light conditions during high periods of driving:

“Altogether, our observations suggest that the time-of-day-associated changes in illumination are not the main contributor to the observed DST effect, but that the circadian misalignment and sleep deprivation associated with DST might play a key role in the acutely increased MVA risk in the DST week. In general, accidents are most likely to occur in the morning hours (between 6am and 8am), which has also been attributed to higher levels of driver sleepiness in the first half of the day than in the latter half of the day during any week of the year. This phenomenon appears to be acutely aggravated by DST transition. The absence of a similarly increased MVA risk in the week after DST further indicates that the illumination conditions play a contributing, but minor role. Analyses of the fall transition back to ST further support this interpretation.”[3]

Crime

This seems to be one area where a move to temporary or permanent DST may be beneficial, but more research needs to be done. One study published in The Review of Economics and Statistics found a seven percent decrease in robberies following the shift to DST. The effects were largest during the hours directly affected by the shift in daylight. The researchers estimated the 2007 DST extension resulted in $59 million in annual social cost savings from avoided robberies.

All of these factors should be considered, and more research should be done, before making a decision about daylight saving time. Next week, we will explore some of the studies on the possible health effects of “springing forward” and “falling back” as well as ideas for further research in Part Two of this blog series.

[1] N Engl J Med 1996; 334:924-925 DOI: 10.1056/NEJM199604043341416

[2] https://doi.org/10.1016/S1389-9457(00)00032-0)

[3] https://doi.org/10.1016/j.cub.2019.12.045