Impact of daylight saving time on road traffic collision risk: a systematic review

The British Sleep Society position statement on Daylight Saving Time in the UK

There is an ongoing debate in the United Kingdom and in other countries about whether twice-yearly changes into and out of Daylight Saving Time should be abolished. Opinions are divided about whether any abolition of Daylight Saving Time should result in permanent Standard Time, or year-long Daylight Saving Time. The British Sleep Society concludes from the available scientific evidence that circadian and sleep health are affected negatively by enforced changes of clock time (especially in a forward direction) and positively by the availability of natural daylight during the morning. Thus, our recommendation is that the United Kingdom should abolish the twice-yearly clock change and reinstate Standard Time throughout the year.

Long-term effects of daylight saving time on driving fatigue

The study of the relationship between Daylight Saving Time (DST) and road safety has yielded contrasting results, most likely in relation to the inability of crash-database approaches to unravel positive (ambient lighting-related) and negative (circadian/sleep-related) effects, and to significant geographical differences in lighting-related effects. The aim of this study was to investigate the effects of DST on driving fatigue, as measured by driving-based, physiological and subjective indicators obtained from a driving simulator experiment. Thirty-seven participants (73 % males, 23 ± 2 years) completed a series of 50-min trials in a monotonous highway environment: Trial 1 was in the week prior to the Spring DST transition, Trial 2 in the following week, and Trial 3 in the fourth week after the transition. Thirteen participants returned for Trial 4, in the week prior to the Autumn switch to civil time, and Trial 5 in the following week. Significant adverse effects of DST on vehicle lateral control and eyelid closure were documented in Trial 2 and Trial 3 compared to Trial 1, with no statistical differences between Trials 2 and 3. Further worsening in vehicle lateral control was documented in Trials 4 and 5. Eyelid closure worsened up to Trial 4, and improved in Trial 5. Participants were unaware of their worsening performance based on subjective indicators. In conclusion, DST has a detrimental impact on driving fatigue during the whole time during which it is in place. Such an impact is comparable, for example, to that associated with driving with a blood alcohol concentration of 0.5 g/L.

All cause and cause specific mortality associated with transition to daylight saving time in US: nationwide, time series, observational study

Objectives

To estimate the association between the transition to daylight saving time and the risks of all cause and cause specific mortality in the US.

Design

Nationwide time series observational study based on weekly data.

Setting

US state level mortality data from the National Center for Health Statistics, with death counts from 50 US states and the District of Columbia, from the start of 2015 to the end of 2019.

Population

13 912 837 reported deaths in the US.

Main outcome measures

Weekly counts of mortality for any cause, and for Alzheimer's disease, dementia, circulatory diseases, malignant neoplasms, and respiratory diseases.

Results

During the study period, 13 912 837 deaths were reported. The analysis found no evidence of an association between the transition to spring daylight saving time (when clocks are set forward by one hour on the second Sunday of March) and the risk of all cause mortality during the first eight weeks after the transition (rate ratio 1.003, 95% confidence interval 0.987 to 1.020). Autumn daylight saving time is defined in this study as the time when the clocks are set back by one hour (ie, return to standard time) on the first Sunday of November. Evidence indicating a substantial decrease in the risk of all cause mortality during the first eight weeks after the transition to autumn daylight saving time (0.974, 0.958 to 0.990). Overall, when considering the transition to both spring and autumn daylight saving time, no evidence of any effect of daylight saving time on all cause mortality was found (0.988, 0.972 to 1.005). These patterns of changes in mortality rates associated with transition to daylight saving time were consistent for Alzheimer's disease, dementia, circulatory diseases, malignant neoplasms, and respiratory diseases. The protective effect of the transition to autumn daylight saving time on the risk of mortality was more pronounced in elderly people aged ≥75 years, in the non-Hispanic white population, and in those residing in the eastern time zone.

Conclusions

In this study, transition to daylight saving time was found to affect mortality patterns in the US, but an association with additional deaths overall was not found. These findings might inform the ongoing debate on the policy of shifting daylight saving time.

Effectiveness of road safety interventions: An evidence and gap map

Background

Road Traffic injuries (RTI) are among the top ten leading causes of death in the world resulting in 1.35 million deaths every year, about 93% of which occur in low- and middle-income countries (LMICs). Despite several global resolutions to reduce traffic injuries, they have continued to grow in many countries. Many high-income countries have successfully reduced RTI by using a public health approach and implementing evidence-based interventions. As many LMICs develop their highway infrastructure, adopting a similar scientific approach towards road safety is crucial. The evidence also needs to be evaluated to assess external validity because measures that have worked in high-income countries may not translate equally well to other contexts. An evidence gap map for RTI is the first step towards understanding what evidence is available, from where, and the key gaps in knowledge.

Objectives

The objective of this evidence gap map (EGM) is to identify existing evidence from all effectiveness studies and systematic reviews related to road safety interventions. In addition, the EGM identifies gaps in evidence where new primary studies and systematic reviews could add value. This will help direct future research and discussions based on systematic evidence towards the approaches and interventions which are most effective in the road safety sector. This could enable the generation of evidence for informing policy at global, regional or national levels.

Search Methods

The EGM includes systematic reviews and impact evaluations assessing the effect of interventions for RTI reported in academic databases, organization websites, and grey literature sources. The studies were searched up to December 2019.

Selection Criteria

The interventions were divided into five broad categories: (a) human factors (e.g., enforcement or road user education), (b) road design, infrastructure and traffic control, (c) legal and institutional framework, (d) post-crash pre-hospital care, and (e) vehicle factors (except car design for occupant protection) and protective devices. Included studies reported two primary outcomes: fatal crashes and non-fatal injury crashes; and four intermediate outcomes: change in use of seat belts, change in use of helmets, change in speed, and change in alcohol/drug use. Studies were excluded if they did not report injury or fatality as one of the outcomes.

Data Collection and Analysis

The EGM is presented in the form of a matrix with two primary dimensions: interventions (rows) and outcomes (columns). Additional dimensions are country income groups, region, quality level for systematic reviews, type of study design used (e.g., case-control), type of road user studied (e.g., pedestrian, cyclists), age groups, and road type. The EGM is available online where the matrix of interventions and outcomes can be filtered by one or more dimensions. The webpage includes a bibliography of the selected studies and titles and abstracts available for preview. Quality appraisal for systematic reviews was conducted using a critical appraisal tool for systematic reviews, AMSTAR 2.

Main Results

The EGM identified 1859 studies of which 322 were systematic reviews, 7 were protocol studies and 1530 were impact evaluations. Some studies included more than one intervention, outcome, study method, or study region. The studies were distributed among intervention categories as: human factors (n = 771), road design, infrastructure and traffic control (n = 661), legal and institutional framework (n = 424), post-crash pre-hospital care (n = 118) and vehicle factors and protective devices (n = 111). Fatal crashes as outcomes were reported in 1414 records and non-fatal injury crashes in 1252 records. Among the four intermediate outcomes, speed was most commonly reported (n = 298) followed by alcohol (n = 206), use of seatbelts (n = 167), and use of helmets (n = 66). Ninety-six percent of the studies were reported from high-income countries (HIC), 4.5% from upper-middle-income countries, and only 1.4% from lower-middle and low-income countries. There were 25 systematic reviews of high quality, 4 of moderate quality, and 293 of low quality.

Authors' Conclusions

The EGM shows that the distribution of available road safety evidence is skewed across the world. A vast majority of the literature is from HICs. In contrast, only a small fraction of the literature reports on the many LMICs that are fast expanding their road infrastructure, experiencing rapid changes in traffic patterns, and witnessing growth in road injuries. This bias in literature explains why many interventions that are of high importance in the context of LMICs remain poorly studied. Besides, many interventions that have been tested only in HICs may not work equally effectively in LMICs. Another important finding was that a large majority of systematic reviews are of low quality. The scarcity of evidence on many important interventions and lack of good quality evidence-synthesis have significant implications for future road safety research and practice in LMICs. The EGM presented here will help identify priority areas for researchers, while directing practitioners and policy makers towards proven interventions.

Driving fatigue increases after the Spring transition to Daylight Saving Time in young male drivers: A pilot study

The Spring transition to Daylight Saving Time (DST) has been associated with several health and road safety issues. Previous literature has focused primarily on the analysis of historical crash and hospitalization data, without investigating specific crash contributing factors, such as driving fatigue. The present study aims to uncover the effects of DST-related circadian desynchrony and sleep deprivation on driving fatigue, by means of a driving simulator experiment. Eighteen participants (all males, age range 21-30 years, mean = 24.2, SD = 2.9) completed two 50-minute trials (at one week distance, same time and same day of the week) on a monotonous highway environment, the second one taking place in the week after the Spring transition to DST. Driving fatigue was evaluated by analysing several different variables (including driving-based, physiological and subjective indices) and by comparison with a historical cohort of pertinent, matched controls who had also undergone two trials, but in the absence of any time change in between. Results showed a considerable rise in fatigue levels throughout the driving task in both trials, but with significantly poorer performance in the post-DST trial, documented by a worsening in vehicle lateral control and an increase in eyelid closure. However, participants seemed unable to perceive this decrease in their alertness, which most likely prevented them from implementing fatigue-coping strategies. These findings indicate that DST has a detrimental effect on driving fatigue in young male drivers in the week after the Spring transition, and provide valuable insights into the complex relationship between DST and road safety.

Lingering impacts on sleep following the Daylight Savings Time transition in the Project Baseline Health Study

Background

The “spring forward” change to Daylight Savings Time (DST) has been epidemiologically linked with numerous health and safety risks in the days following the transition, but direct measures of sleep are infrequently collected in free-living individuals.

Methods

The Project Baseline Health Study (PBHS), a prospective, multicenter, longitudinal representative U.S. cohort study that began in 2017 launched a Sleep Mission in March 2021 to characterize sleep using patient-reported and wearable device measures, in free-living circumstances during the DST switch. Estimated sleep period duration, subjective restedness, and sleep quality were compared before and after the DST transition during specified timeframes.

Results

Of the total PBHS population of 2502 participants, 912 participants received an invitation and 607 responded by March 6th. Among those, 420 participants opted into the Sleep Mission (69.2%). The transition to DST resulted in both acute and lingering impacts on sleep. Acute effects included a 29.6 min reduction in sleep period (p = 0.03), increases in the proportion of patients who reported ‘sleeping poorly’ (from 1.7 to 13.6% [p < 0.01]), and with scores falling into the ‘unrested’ category (from 1.7 to 8.5% [p = 0.046]). There was also a downward trend in the proportion of participants reporting being rested in the morning following the DST transition (from 62.7% on March 7 to 49.2% on March 14 [p = 0.10]). Lingering effects included a 18.7% relative decrease in the daily likelihood of participants reporting restedness (from 49.2% in the week prior to the DST transition to 40.0% in the week after [p < 0.01]).

Conclusion

The DST transition is associated with an acute reduction in sleep period, as well as an increased proportion of individuals reporting poor sleep and unrestedness. The DST transition also resulted in lingering impacts on self-reported restedness, lasting into the week following the transition. This work adds to a growing understanding of the persistence of impacts on sleep health metrics due to the DST transition.

It is time to abolish the clock change and adopt permanent standard time in the United States: a Sleep Research Society position statement

Daylight saving time (DST) refers to the practice of advancing clock time by 1 h each spring, with a return (setting back) to standard time (ST) each fall. Numerous sleep and circadian societies other than the Sleep Research Society have published statements in support of permanent ST, and permanent ST has also received support from multiple medical societies and organizations. This perspective discusses the positive and negative health and economic consequences of permanent DST, permanent ST, and maintaining the status quo (DST for part of the year). After a thorough review of the existing literature, the SRS advocates the adoption of permanent ST.

Traffic crash changes following transitions between daylight saving time and standard time in the United States: New evidence for public policy making

INTRODUCTION

This study examined the impact of daylight saving time changes on traffic crashes in the United States. Using a data-driven regression analysis approach, the study analyzed 2014-2016 crash data from six states spanning all four major time zones in the contiguous United States.

METHOD

The researchers developed regression models for a number of analysis scenarios and by days of week separately. Based on the crash data, the team used an eight-week impact period for the spring time change and a four-week impact period for the fall time change.

RESULTS

The regression analysis showed that the spring time change was followed by an overall crash reduction of 18% during the eight-week period immediately after the time change, with a considerably higher crash reduction for freeway crashes (24%), rural crashes (24%), or non-intersection crashes (21%). The time change back to SDT in fall was followed by a 6% overall crash increase during the following four weeks, with considerably higher increases for freeway crashes (15%), non-intersection crashes (9%), nighttime crashes (28%), single-vehicle crashes (28%), and crashes in urban areas (12%). This study provides additional insights, including in many cases more comprehensive knowledge on how the changes to and from DST each year affect roadway traffic crashes.

PRACTICAL APPLICATIONS

The findings of this project further add to the current understanding on how the time changes affect public health in the form of traffic crashes. They also serve as additional evidence for public policy makers to better weigh the benefits and impacts associated with the time changes in the United States for relevant policy makings.

Daylight saving time affects European mortality patterns

Daylight saving time (DST) consists in a one-hour advancement of legal time in spring offset by a backward transition of the same magnitude in fall. It creates a minimal circadian misalignment that could disrupt sleep and homoeostasis in susceptible individuals and lead to an increased incidence of pathologies and accidents during the weeks immediately following both transitions. How this shift affects mortality dynamics on a large population scale remains, however, unknown. This study examines the impact of DST on all-cause mortality in 16 European countries for the period 1998-2012. It shows that mortality decreases in spring and increases in fall during the first two weeks following each DST transition. Moreover, the alignment of time data around DST transition dates revealed a septadian mortality pattern (lowest on Sundays, highest on Mondays) that persists all-year round, irrespective of seasonal variations, in men and women aged above 40.

Daylight savings time transition and the incidence of femur fractures in the older population: a nationwide registry-based study

Background

Daylight Savings Time (DST) transition is known to cause sleep disruption, and thus may increase the incidence of injuries and accidents during the week following the transition. The aim of this study was to assess the incidence of femur fractures after DST transition.

Methods

We conducted retrospective population-based register study. All Finnish patients 70 years or older who were admitted to hospital due to femur fracture between 1997 and 2020 were gathered from the Finnish National Hospital Discharge Register. Negative binomial regression with 95% confidence intervals (CI) was used to evaluate the incidence of femur fractures after DST transition.

Results

The data included a total of 112,658 femur fractures during the study period between 1997 and 2020, with an annual mean (SD) of 4,694 (206) fractures. The incidence of femur fractures decreased at the beginning of the study period from 968 to 688 per 100,000 person-years between 1997 and 2007. The weekly mean of femur fractures remained lower during the summer (from 130 to 150 per 100,000 person-weeks) than in winter (from 160 to 180 per 100,000 person-weeks). Incidence rate ratio for the Monday following DST transition was 1.10 (CI [0.98-1.24]) in spring and 1.10 (CI [0.97-1.24]) in fall, and for the whole week 1.07 (CI [1.01-1.14]) in spring and 0.97 (CI [0.83-1.13]) in fall.

Conclusion

We found weak evidence that the incidence of femur fractures increases after DST transition in the spring.

Impact of DST (Daylight Saving Time) on Major Trauma: A European Cohort Study

(1) Background: Approximately 73 countries worldwide implemented a daylight saving time (DST) policy: setting their clocks forward in spring and back in fall. The main purpose of this practice is to save electricity. The aim of the present study was to find out how DST affects the incidence and impact of seriously injured patients. (2) Methods: In a retrospective, multi-center study, we used the data recorded in the TraumaRegister DGU^® (TR-DGU) between 2003 and 2017 from Germany, Switzerland, and Austria. We compared the included cases 1 week before and after DST. (3) Results: After DST from standard time to summertime, we found an increased incidence of accidents of motorcyclists up to 51.58%. The result is consistent with other studies. (4) Conclusion: However, our results should be interpreted as a tendency. Other influencing factors, such as time of day and weather conditions, were not considered.

Effect of Daylight Saving Time clock shifts on white-tailed deer-vehicle collision rates

To devise effective measures for reducing hazardous wildlife-vehicle collisions, it is necessary to know when during the year accidents occur most frequently, and what factors cause the seasonal patterns. Daylight Saving Time (DST) 1-h clock-shifts around the spring and fall equinoxes at temperate zone latitudes are associated with increased vehicle accidents, attributed to driver error caused by disrupted sleep patterns and changes in visibility during peak driving times. Collision with deer is a significant cause of motor vehicle accidents in North America; in New York State alone, 65,000 vehicle accidents annually are caused by collision with white-tailed deer (Odocoileus virginianus). We asked whether white-tailed deer-vehicle collisions (DVC) increased in frequency after DST clock shifts in New York State, by analyzing 35,167 New York State DVC reports from 2005 to 2007. For the spring, when the clock is shifted an hour forward relative to sunrise (i.e. later sunrise and sunset), there was either no change or possibly a small decrease in workweek evening DVC after the clock shift. For fall, when the clock is shifted an hour back relative to sunrise (i.e. earlier sunrise and sunset), the DVC rate was far higher than spring. The DVC rate was higher after the clock shift than before, caused in part by an ongoing seasonal trend for increasing DVC associated with deer behavior around the time of rut, peaking about two weeks after the clock shift. However, there was also a reduction in workweek morning DVC after clock-shift, but an even greater increase in DVC in the evening. DVC rates are highest around dusk and during the fall, and the fall DST clock-shift caused more workweek commuter traffic to coincide with the annual hourly period of peak risk of DVC. We conclude that in New York State, DST clock-shift results in an increase in the number of DVC, and therefore injuries and property damage associated with such accidents. The justification for DST clock-shifts is controversial; when evaluating the benefits and costs, one should include the consequences for risk of wildlife-vehicle collisions, especially in regions where ungulate-vehicle accidents are frequent, and clock-shifts coincide with the rut or other periods of peak accident risk.

Daylight Saving Time: Pros and Cons

The original rationale for the adoption of daylight saving time (DST) was to conserve energy; however, the effects of DST on energy consumption are questionable or negligible. Conversely, there is substantial evidence that DST transitions have the cumulative effect on sleep deprivation with its adverse health effects. In light of current evidence, the European Commission in 2018 decided that biannual clock change in Europe would be abolished. Current indirect evidence supports the adoption of perennial standard time, which aligns best with the human circadian system and has the potential to produce benefits for public health and safety.

Why Should We Abolish Daylight Saving Time?

Local and national governments around the world are currently considering the elimination of the annual switch to and from Daylight Saving Time (DST). As an international organization of scientists dedicated to studying circadian and other biological rhythms, the Society for Research on Biological Rhythms (SRBR) engaged experts in the field to write a Position Paper on the consequences of choosing to live on DST or Standard Time (ST). The authors take the position that, based on comparisons of large populations living in DST or ST or on western versus eastern edges of time zones, the advantages of permanent ST outweigh switching to DST annually or permanently. Four peer reviewers provided expert critiques of the initial submission, and the SRBR Executive Board approved the revised manuscript as a Position Paper to help educate the public in their evaluation of current legislative actions to end DST.

Response to Martín-Olalla

Vetter et al. respond to Martín-Olalla's comment about their study linking motor vehicle fatalities to the transition to Daylight Saving Time.

A Chronobiological Evaluation of the Acute Effects of Daylight Saving Time on Traffic Accident Risk

There is evidence that the spring Daylight Saving Time (DST) transition acutely increases motor vehicle accident (MVA) risk ("DST effect"), which has been partly attributed to sleep deprivation and circadian misalignment [1-6]. Because spring DST also shifts clock time 1 h later, mornings are darker and evenings brighter, changing illumination conditions for peak traffic density. This daytime-dependent illumination change ("time of day effect") is hypothesized to result in DST-associated afternoon and evening accident risk reductions [2, 5, 7]. Furthermore, sunrise and local photoperiod timing depend on position in time zone. The sun rises at an earlier clock time in the eastern regions of a given time zone than in the western regions, which is thought to induce higher levels of circadian misalignment in the west than in the east ("time zone effect") [8, 9]. This study evaluated the acute consequences of the DST transition on MVAs in a chronobiological context, quantifying DST, time of day, and time zone effects. We used large US registry data, including 732,835 fatal MVAs recorded across all states (1996-2017), and observed that spring DST significantly increased fatal MVA risk by 6%, which was more pronounced in the morning and in locations further west within a time zone. DST-associated MVA risk increased even in the afternoon hours, despite longer daylight hours. The MVA risk increase waned in the week subsequent to DST, and there were no effects of the fall-back transition to Standard Time (ST) on MVA risk, further supporting the hypothesis that DST-transition-associated, preventable circadian misalignment and sleep deprivation might underlie MVA risk increases.

Daylight Saving Time and Artificial Time Zones - A Battle Between Biological and Social Times

Many regions and countries are reconsidering their use of Daylight Saving Time (DST) but their approaches differ. Some, like Japan, that have not used DST over the past decades are thinking about introducing this twice-a-year change in clock time, while others want to abolish the switch between DST and Standard Time, but don't agree which to use: California has proposed keeping perennial DST (i.e., all year round), and the EU debates between perennial Standard Time and perennial DST. Related to the discussion about DST is the discussion to which time zone a country, state or region should belong: the state of Massachusetts in the United States is considering switching to Atlantic Standard Time, i.e., moving the timing of its social clock (local time) 1 h further east (which is equivalent to perennial DST), and Spain is considering leaving the Central European Time to join Greenwich Mean Time (GMT), i.e., moving its social timing 1 h further west. A wave of DST discussions seems to periodically sweep across the world. Although DST has always been a political issue, we need to discuss the biology associated with these decisions because the circadian clock plays a crucial role in how the outcome of these discussions potentially impacts our health and performance. Here, we give the necessary background to understand how the circadian clock, the social clock, the sun clock, time zones, and DST interact. We address numerous fallacies that are propagated by lay people, politicians, and scientists, and we make suggestions of how problems associated with DST and time-zones can be solved based on circadian biology.