“Changing the clocks twice a year increases workplace injuries and road accidents.”

• Barnes & Wagner (2009, Journal of Applied Psychology) analyzed US Mine Safety and Health Administration data (1983–2006) and found that on the Monday after the spring-forward transition, workers slept ~40 minutes less, injuries rose ~5.7%, and work days lost to injuries rose ~68%; no comparable effect was found after the fall transition.
• Fritz et al. (2020, Current Biology) examined 732,835 US fatal crashes (1996–2017) and found a 6% increase in fatal traffic accident risk in the week following the spring DST transition, with the effect strongest in the morning and in the western (later-sunrise) edges of time zones — a pattern consistent with a circadian/sleep-loss mechanism rather than coincidence.
• Smith (2016, American Economic Journal: Applied Economics) used a regression-discontinuity design on US fatal crash data and estimated roughly a 5–6.5% increase in fatal crash risk for the six days after spring forward, attributing the effect primarily to sleep deprivation rather than ambient light.
• Varughese & Allen (2001, Sleep Medicine) found a significant increase in US fatal traffic accidents on the Monday following the spring shift, and also reported an increase on the Sunday of the autumn shift (attributed to extended late-night activity).
• The American Academy of Sleep Medicine's 2020 position statement, reviewing the literature, concluded that acute transitions into and out of DST are associated with increased motor vehicle crashes and other adverse safety/health outcomes, and advocated abolishing the twice-yearly change in favor of permanent standard time.
• The US Congressional Research Service's overview of DST notes research linking the transitions to sleep disruption and increased accident and injury risk, indicating the association is recognized in policy analysis, not just advocacy literature.

• A systematic review in BMJ Open (Carey & Sarma, 2017) of 24 studies concluded the evidence on DST and road traffic collisions is mixed and of generally low quality: some studies found increases after the spring shift, others found no effect or even decreases, and several studies on the autumn shift found reduced collision risk.
• Most of the robust evidence concerns only the spring (lose-an-hour) transition. The claim as written implies both annual changes raise risk, but the autumn transition often shows no increase or a short-term decrease in crashes, so the harm is asymmetric rather than symmetric across the two changes.
• Effect sizes are small in absolute terms and short-lived — typically confined to the first few days to one week after the change — and some of the apparent crash increase in autumn is attributable to earlier evening darkness (a lighting effect) rather than to the act of changing clocks itself.
• The workplace-injury finding rests heavily on a single occupational dataset (US underground mining, an unusually sleep- and shift-sensitive industry); replication across other industries and countries is limited, so generalizing to 'workplace injuries' broadly overstates the evidence base.
• Some national studies (e.g., Finnish data) found no statistically significant change in road traffic accidents around either DST transition, showing the effect is not universally detectable.
• Pre-2000s studies that popularized the claim (e.g., Coren's analyses) used crude time-series methods and have been criticized for failing to control for seasonality, weekday effects and traffic volume.

85/100 — the lab’s own confidence in the score above, not a second reading of the claim.

Journal of Applied Psychology (via PubMed/NIH)journal · 92 · Current Biology (Cell Press)journal · 93 · American Economic Journal: Applied Economics (AEA)journal · 90 · BMJ Openjournal · 90 · Sleep Medicine (Elsevier)journal · 82 · Congressional Research Servicegov · 88

• A peer-reviewed Journal of Applied Psychology study using U.S. mine-injury data found that the spring shift to daylight saving time was associated with less sleep and a significant increase in workplace injuries and injury severity on the following Monday; this supports the workplace-injury part of the claim, though mainly for the spring transition and a specific industry.
• A 2020 Current Biology study of U.S. fatal crash data found about a 6% increase in fatal motor-vehicle crashes in the week after the spring daylight-saving transition, supporting the road-accident part of the claim for at least fatal crashes shortly after clocks move forward.
• A New England Journal of Medicine letter found traffic accidents rose after the spring clock change and fell after the autumn change, consistent with the idea that sleep loss at the spring transition can increase road risk.
• The American Academy of Sleep Medicine position statement cites increased motor-vehicle crashes and workplace injuries after the spring daylight-saving transition as part of its rationale for favoring permanent standard time.
• CDC/NIOSH guidance for workers and employers warns that the spring daylight-saving transition can increase fatigue-related safety risk and cites research linking the transition to workplace injuries.

• The strongest evidence is concentrated on the spring 'forward' change, when people lose an hour of sleep; the autumn 'back' change often shows smaller, no, or even opposite effects. So the wording 'twice a year' can overstate the evidence if read to mean both clock changes increase injuries and crashes.
• Workplace-injury evidence is not as broad as the claim sounds: a key study used mining-injury records, so it is suggestive but not proof that all workplaces experience the same effect.
• Road-accident findings are not perfectly uniform across countries, methods, and outcome definitions. A Finnish study in Journal of Environmental and Public Health found no significant increase in road traffic accidents after daylight-saving transitions.
• Some road-safety analyses distinguish between the short-term transition effect and the broader effect of more evening daylight; one Accident Analysis & Prevention study estimated that year-round daylight saving time could reduce pedestrian and vehicle-occupant fatalities, which complicates a simple 'DST increases accidents' framing.

84/100 — the lab’s own confidence in the score above, not a second reading of the claim.

Journal of Applied Psychology / American Psychological Associationjournal · 90 · Current Biologyjournal · 92 · New England Journal of Medicinejournal · 88 · Journal of Environmental and Public Healthjournal · 78 · Accident Analysis & Preventionjournal · 86

• A 2020 study published in Current Biology analyzed over 732,000 fatal traffic accidents in the U.S. and found a consistent 6% increase in fatal crash risk during the workweek immediately following the spring transition to Daylight Saving Time (DST).
• A widely cited 2009 study in the Journal of Applied Psychology analyzed data from the National Institute for Occupational Safety and Health (NIOSH) and found that workers sleep an average of 40 minutes less on the Monday following the spring clock change. This sleep loss strongly correlated with a spike in both the frequency and severity of workplace injuries on that day.
• While the spring change triggers accidents via sleep deprivation, the autumn 'fall back' transition is associated with an acute spike in evening pedestrian and traffic accidents due to the sudden shift of darkness into the evening rush hour commute.
• The American Academy of Sleep Medicine (AASM) has issued position statements advocating for the elimination of bi-annual clock changes, citing overwhelming evidence that the transitions cause acute disruptions to circadian rhythms, leading to increased risks of motor vehicle crashes, workplace errors, and cardiovascular events.

• The autumn clock change (ending DST), which yields an extra hour of sleep, does not cause the same sleep-deprivation-related spike in morning accidents and workplace injuries. Some studies even note a minor decrease in morning accidents immediately following the autumn change.
• Some researchers argue that maintaining DST year-round might reduce the *total* annual number of traffic fatalities by providing more ambient light during evening commutes, suggesting that while the *transitions* cause acute spikes, daylight itself mitigates overall crash rates.

98/100 — the lab’s own confidence in the score above, not a second reading of the claim.

National Institutes of Health (NIH) / PubMedgov · 95 · National Institutes of Health (NIH) / PubMedgov · 95 · National Institutes of Health (NIH) / PubMedgov · 98

• A peer-reviewed study of U.S. mining injuries found that the Monday after the spring clock change was associated with 3.6 additional injuries, greater injury severity, 40 minutes less sleep, and about 2,649 additional lost workdays; it found no comparable effect after the autumn change.[1][2]
• A U.S. study of 732,835 fatal motor-vehicle crashes from 1996–2017 found a 6% increase in fatal-crash risk after the spring transition, with the effect concentrated in the following week and no effect after the autumn transition.[3]
• A New Zealand analysis of 12.6 million accident claims reported higher road-accident rates after the spring transition—16% higher on Sunday, 12% higher on Monday, and 6% higher on subsequent weekdays—while finding limited workplace effects.[4]
• The proposed mechanism is plausible: the spring change removes an hour of sleep and creates temporary circadian misalignment, which can impair alertness and reaction time.[1][2][3]

• A peer-reviewed U.S. study covering road accidents around transitions from 1981–2006 found that neither the spring nor autumn transition increased road-accident totals.[5]
• A 2019 reappraisal using large U.S. accident datasets found no significant association between the spring transition and fatal or nonfatal accident rates.[6]
• A 2023 Australian study found no effect of either transition, or of long-term daylight-saving observance, on road fatalities, although accident timing shifted with ambient light.[7]
• A 2023 study using all recorded vehicle accidents in Greece found no change in total or minor accidents after entering daylight saving time, a reduction in serious accidents, and only a weak increase in fatal accidents.[8]
• The workplace-injury evidence is narrower than the claim: the strongest positive study examined U.S. mining injuries and found an effect after losing an hour in spring, not a consistent increase after both annual clock changes.[1][2]

93/100 — the lab’s own confidence in the score above, not a second reading of the claim.

Journal of Applied Psychologyjournal · 96 · American Psychological Associationother · 90 · Current Biologyjournal · 95 · University of Aucklandedu · 88 · BMC Public Healthjournal · 93 · Sleepjournal · 85 · Economic Inquiryjournal · 93 · Health Economicsjournal · 93

• A 2020 Current Biology analysis of U.S. fatal-crash data found a 6% increase in the workweek after the spring transition, linked to sleep loss and circadian misalignment.
• A 2009 Journal of Applied Psychology study of mining records reported 5.7% more workplace injuries and 67% more lost workdays on the Monday after clocks spring forward.
• The American Academy of Sleep Medicine 2020 position statement lists higher motor-vehicle crash and workplace-injury risk among the reasons to end biannual clock changes.

• A 2017 BMJ Open systematic review found the literature on DST and road collisions mixed and of generally low quality, with no consistent overall effect.
• The autumn 'fall-back' change is often associated with fewer (not more) accidents because of the extra hour of sleep, so both yearly changes do not uniformly increase harm.
• Documented spikes are small, last only a few days, and some analyses attribute them to residual confounding (weather, traffic volume, seasonal trends) rather than the clock shift itself.

72/100 — the lab’s own confidence in the score above, not a second reading of the claim.

Current Biologyjournal · 95 · Journal of Applied Psychologyjournal · 90 · BMJ Openjournal · 92