Is Daylight Saving Time a Factor in Fatal Car Crashes?

TL;DR

• Yes. Daylight savings traffic accidents increase measurably after the spring time change. A University of Colorado Boulder study of 732,835 fatal crashes found a 6% spike in fatal accident risk during the workweek after clocks spring forward, accounting for roughly 28 additional deaths per year.
• This guide covers what the research shows, why both the spring and fall changes affect crash rates differently, who is most at risk, and what drivers and injury victims need to know.

Daylight saving time is treated as a minor inconvenience. The research says otherwise. Every spring, when clocks move forward one hour, something measurable happens on American roads: more people die.

Daylight savings car accidents are not a statistical anomaly. Multiple independent studies using decades of crash data have found a consistent, significant increase in fatal traffic incidents in the days immediately following the spring time change. Sleep deprivation, altered commute timing, and reduced morning visibility all converge at once.

Understanding why daylight savings time car accidents spike matters for drivers, policymakers, and anyone evaluating fault after a crash during this high-risk period.

What Does the Research Say About Daylight Savings Traffic Accidents?

The most comprehensive study to date was published in Current Biology by researchers at the University of Colorado Boulder. They analyzed 732,835 fatal crashes from 1996 to 2017 through NHTSA’s FARS database and found a consistent 6% increase in fatal accident risk during the workweek following the spring time change.

That 6% translates to approximately 28 additional deaths each year attributable to the time change alone. The effect was most pronounced in the morning hours immediately following the change and faded over the following two weeks as drivers adjusted to the new schedule.

A separate study published in Accident Analysis and Prevention found even sharper immediate effects: daylight savings time car accidents increased 16% on the first day after the DST transition and 12% on the second day. These figures reflect total crashes, not just fatal ones.

Spring vs. Fall: Does the Direction of the Change Matter?

The spring and fall transitions affect road safety in different ways, and the question of whether there are more accidents in the day or night is central to understanding why.

IIHS research shows the spring change raises motor-vehicle occupant crashes by 12% over five weeks; the fall change cuts them 7.1%. Pedestrian deaths rise 13% after fall back. Understanding who is liable in these drowsy driving crashes matters for injured claimants.

The net effect: clocks changing in either direction creates a safety problem. It is just a different population bearing the risk each time.

Why Do Daylight Savings Car Accidents Increase After the Time Change?

Three factors converge in the days after the spring change to elevate crash risk. None of them individually would produce a measurable statistical effect. Together, they consistently do.

Sleep Deprivation and Circadian Disruption

The spring change removes one hour of sleep from most people in a single night. For drivers who already operate close to insufficient sleep, that deficit pushes reaction times, decision-making, and sustained attention into impaired territory.

Most people underestimate how much a single hour of lost sleep affects their driving. Research consistently shows that being awake for 18 hours produces impairment equivalent to a blood alcohol concentration of 0.05, well below the legal limit but still meaningfully degraded.

The AAA Foundation for Traffic Safety found that 17.6% of all fatal crashes between 2017 and 2021 involved a drowsy driver, resulting in more than 29,800 deaths. AAA research shows drowsy driving impairs the same cognitive functions as alcohol intoxication.

Circadian disruption extends beyond a single night. Sleep patterns can take up to two weeks to fully adjust after a time change, which is consistent with the research showing crash rates returning to baseline after about that same period.

This two-week window is not a safe period to ignore. The risk is highest in the first three days, then gradually declines as sleep debt is repaid. Drivers with pre-existing sleep deficits face a compounded risk during this window.

Darker Morning Commutes

Before the spring time change, many commuters travel to work in daylight. Immediately after, those same commutes happen in darkness. The University of Colorado Boulder study identified darker morning commutes as a significant contributor to the post-DST crash spike, particularly in the first few days after the change.

This connects to the question of whether there are more accidents in the day or night. The National Safety Council reports roughly 50% of traffic fatalities occur at night despite night driving representing about 25% of miles driven. DST converts daytime commutes to nighttime commutes instantly, with no adjustment period.

Geography Makes It Worse for Some Drivers

The CU Boulder study found that western residents of each time zone face higher DST crash risk. They experience the latest sunrises, making morning darkness more severe after the spring change.

Daylight Saving Time and Car Accidents: Spring vs. Fall at a Glance

Source: University of Colorado Boulder (Current Biology, 2020); Insurance Institute for Highway Safety (IIHS).

Are There More Accidents in the Day or Night Generally?

Outside of DST transitions, nighttime driving is consistently more dangerous on a per-mile basis than daytime driving. NHTSA data shows that roughly 50% of fatal traffic crashes occur at night, even though nighttime driving represents only about a quarter of total miles traveled on U.S. roads.

In absolute numbers, more total crashes happen during the day because traffic volume is higher. But the probability of a crash being fatal is significantly elevated at night. Reduced visibility, more impaired drivers, and higher speeds on emptier roads all contribute to the disproportionate nighttime fatality rate.

DST amplifies this dynamic twice a year by shifting the boundary between when people drive and when it is dark. The spring change pushes morning commuters into darkness. The fall change pushes evening commuters, pedestrians, and cyclists into darkness. Neither group has prepared for the change.

Infrastructure does not adjust either. Street lighting, crosswalk timing, and school bus schedules were calibrated for the prior lighting conditions. The mismatch between when people travel and when the environment is lit for safe travel creates a predictable but largely unaddressed gap in road safety.

For pedestrians and cyclists, the fall change is particularly dangerous. The IIHS data showing a 13% increase in pedestrian and cyclist fatalities after fall back reflects the reality that these road users lose protective daylight during peak commute hours with no warning and no behavioral adjustment period.

Daylight Saving Time Car Accidents and Legal Liability

When a daylight saving time car accident results in serious injury, the legal framework that applies is the same as any other personal injury case. The time change does not reduce a driver’s duty of care or create a legal excuse for causing a crash.

A driver who causes a collision while drowsy faces the same liability analysis as any other negligent driver. Daylight savings traffic accidents caused by fatigue are treated no differently. Courts assess whether the driver breached their duty of care, and drowsiness is a foreseeable risk drivers are expected to manage.

This matters for injured plaintiffs because it directly affects how damages are calculated and what recoverable losses look like in a claim involving a drowsy or impaired driver.

Evidence that can support a DST-related drowsy driving claim includes the time of day, the day of the week relative to the time change, witness accounts of erratic driving behavior, electronic data from the vehicle, and any admissions by the driver about fatigue.

Expert testimony from accident reconstruction specialists and sleep medicine professionals can also be relevant. When a crash occurs on a Tuesday morning three days after the spring change, the statistical context reinforces the claim that impairment was a contributing factor.

What Should You Do if You Are Injured in a Daylight Savings Time Car Accident?

The steps to take after a DST crash are the same as after a car accident: call 911, seek medical attention, document the scene, and contact a personal injury attorney before speaking with the other driver’s insurer.

The DST context can strengthen a claim. Daylight saving time car accidents occur in a statistically anomalous window for driver impairment. If the crash happened in morning commute hours in the days after the spring change, that timing is relevant to establishing the at-fault driver’s state.

Injured plaintiffs may also face financial pressure while their case is pending. Pre-settlement funding provides a non-recourse cash advance against the expected settlement value, allowing injured parties to manage expenses without settling early for less than the claim is worth.

Conclusion

Daylight saving time car accidents are not random. The research consistently shows that the spring time change creates a measurable, preventable spike in fatal crashes driven by sleep loss, disrupted circadian rhythms, and darker morning commutes.

Drivers can reduce risk by prioritizing sleep before and after the change and allowing extra travel time. Daylight savings car accidents are predictable, which means they are preventable. If injured by a drowsy driver after the time change, the law provides the same recourse as any other negligence claim.

At Gain Servicing, injured plaintiffs waiting on a personal injury settlement can access non-recourse pre-settlement funding to manage expenses while their case resolves.

FAQs

1. Do daylight savings time car accidents increase after the spring change?

Yes. A University of Colorado Boulder study of 732,835 fatal crashes found a 6% increase in fatal accident risk during the workweek following the spring DST change. The effect peaks in the morning hours of the first few days and returns to baseline after about two weeks as sleep patterns adjust.

2. Why do daylight saving time traffic accidents increase?

The primary cause is sleep deprivation from losing one hour of sleep combined with circadian disruption that can take up to two weeks to resolve. Darker morning commutes immediately after the change add reduced visibility to an already impaired driver population, producing the documented crash spike.

3. Are there more accidents in the day or night overall?

More total crashes happen during daylight hours because traffic volume is higher. However, fatal crashes are disproportionately nighttime events. NHTSA data shows approximately 50% of traffic fatalities occur at night despite nighttime driving accounting for only about 25% of total miles traveled.

4. Does the fall time change also increase car accidents?

The fall change shifts risk rather than eliminating it. IIHS research found motor-vehicle occupant fatalities decrease 7.1% in the five weeks after the fall change, but pedestrian and cyclist fatalities increase 13% as evening commutes shift into darkness. The net road safety outcome depends on which group you are examining.

5. Who is most at risk from daylight saving time car accidents?

Morning commuters are most at risk after the spring change, particularly those who live in the western portions of their time zone where sunrise is latest. After the fall change, pedestrians and cyclists face elevated risk as evening darkness arrives earlier. Drivers already operating on insufficient sleep are most vulnerable in both transitions.

6. Can a drowsy driver be held liable for a crash after DST?

Yes. A driver’s duty of care does not diminish because of a time change. Courts treat drowsy driving as a foreseeable, manageable risk that drivers are expected to address. Evidence such as the time of crash, driver behavior reports, and vehicle data can all support a drowsy driving liability claim.

7. What should I do if I am injured in a car accident after daylight saving time?

Seek medical attention immediately, document the scene and injuries, report the crash to police, and contact a personal injury attorney before communicating with the at-fault driver’s insurer. The post-DST timing of the crash may be a relevant context for establishing the driver’s impaired state at the time of the incident.