Surge in Fatal Car Accidents with Springing Forward to Daylight Savings Time Interview with:

Josef Fritz, Ph.D. PostDoctoral Fellow Circadian and Sleep Epidemiology Laboratory Department of Integrative Physiology University of Colorado Boulder

Dr. Fritz

Josef Fritz, Ph.D.
PostDoctoral Fellow
Circadian and Sleep Epidemiology Laboratory
Department of Integrative Physiology
University of Colorado Boulder What is the background for this study?

Response: Daylight Saving Time (DST), the practice of setting clocks forward by an hour during the summer months and an hour back again during the winter months, is currently given a lot of attention, also because of world-wide discussions whether DST should be abolished, extended, or kept year-around. Since its introduction, mainly with the intention to reduce energy consumption, the spring DST transition has been associated with various adverse outcomes within the first few days after the transition, including an increased risk of myocardial infarctions, strokes, and workplace accidents. When we reviewed the evidence linking DST to traffic accident risk, however, results were not that clear-cut. We thus decided to take a closer look, based on one of the most extensive datasets so far, with 22 years of fatal traffic accident recordings across the US.

We also aimed at decomposing the potential overall effect of Daylight Saving Time on traffic accident risk, given that both environmental illumination levels, and geographical factors such as position in time zone, may play a role in modulating fatal traffic accident risk associated with DST, but explicit and concurrent examination of these factors has so far been lacking. What are the main findings?

Response: Our analysis of a comprehensive collection of all fatal traffic accidents over the last 22 years across all US States that observe Daylight Saving Time demonstrated that the spring DST transition increased the risk of fatal traffic accidents by approximately 6% in the week following transition. The risk increase was highest in the morning, and more pronounced in western regions of time zones. All these effects were observed acutely, meaning that the traffic accident risk returned to the year-round baseline risk after about one week. What should readers take away from your report?

Response: The acute adverse effects of Daylight Saving Time on traffic accident risk are real, and can be prevented. Although the observed effects appear to be of moderate size and are not long-lasting, we must not forget that DST transition affects billions of people every year, and thus small changes in risk can have a substantial public health impact. Specifically, our models show, that, alone in the US, about 28 fatal traffic accidents occurring in the week after spring DST transition could be prevented each year. Following the evidence of our analysis, and taking into account other reports on adverse effects of time changes on health outcomes, sleep, and performance, policy makers should consider abolishing the annual switch to and from DST. This is further supported by our findings that Daylight Saving Time DST transition effects on fatal traffic accident risk are more pronounced in Western parts of a given time zone, than in the Eastern parts, creating inequalities within time zones, which are unnecessary and preventable. What recommendations do you have for future research as a result of this work?

Response: We think the next steps are twofold:

  • First, we want to understand and characterize Daylight Saving Time exposure better on a population level, and by using individual-level information from medical and accident databases, we will be in an even better position to identify those who are most vulnerable and affected by DST.
  • Second, we need to better understand the physiological consequences of the “mini-jetlag” induced by DST transitions. Is there anything else you would like to add?

Our data only supports the conclusion that we should stop switching between Standard and Daylight Saving Time and does not directly relate to the question if permanent Standard Time or permanent DST is to be preferred. Nevertheless, we want to add that, generally speaking, there is evidence that it would be better for sleep, the body clock, and overall health to have more morning light and less evening light, as is the case under permanent Standard Time. Therefore, our team, as well as the majority of chronobiologists, prefer permanent Standard Time. For those who want to know more details, the Society of Research on Biological Rhythms’ (SRBR) has recently issued a position paper in favor of permanent Standard Time, which can be found here:

Any disclosures?

I have no disclosures.


Josef Fritz, Trang VoPham, Kenneth P. Wright, Céline Vetter.A Chronobiological Evaluation of the Acute Effects of Daylight Saving Time on Traffic Accident Risk.Current Biology, 2020; DOI: 10.1016/j.cub.2019.12.045

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Last Updated on February 3, 2020 by Marie Benz MD FAAD