tangentially related, Dr. Andrew Huberman shared a video in which he asserts that exposing one's eyes to sunlight very soon after waking is "good for your brain" (essentially):
https://www.youtube.com/watch?v=h2aWYjSA1Jchttps://grok.com/share/c2hhcmQtMi1jb3B5_f52a6bb5-dc0d-4a3a-8...
Multiple peer-reviewed studies and analyses indicate an increase in traffic accidents—particularly fatal ones—following the spring transition to DST. This is often attributed to acute sleep deprivation (losing one hour of sleep), circadian rhythm disruption, and altered light conditions during peak commuting hours, which can impair alertness, reaction times, and visibility. Key findings include:
A large-scale U.S. study analyzing over 732,000 fatal motor vehicle accidents from 1996 to 2017 (published in Current Biology, 2020) reported a consistent 6% increase in fatal crash risk during the workweek immediately following the spring DST transition, equating to approximately 28 additional deaths annually in the U.S. The effect was more pronounced in western regions of time zones and persisted into afternoon hours despite longer evening daylight.
Other research has documented short-term spikes, such as increases of 16% on the first day and 12% on the second day after the spring change in some analyses, or broader elevations in fatal crashes linked to the "DST effect."
Systematic reviews and meta-analyses confirm short-term elevations in collision risk post-spring transition in many (though not all) contexts, with some evidence of higher fatal accident rates in the U.S. specifically.
The fall transition back to Standard Time shows more mixed or opposite patterns: some studies report small increases in certain crash types (e.g., due to darker evening commutes increasing pedestrian or deer-vehicle collisions), while others note decreases in vehicle-occupant fatalities or no net increase overall.
A 2017 systematic review of road traffic collision risk found inconsistent short-term effects across studies (some showing increases, decreases, or no change), but long-term analyses often suggested a net safety benefit from DST periods due to evening light. Recent Insurance Institute for Highway Safety (IIHS) research (covering 2010–2019 U.S. data) indicated that spring DST increases fatal motor-vehicle occupant crashes (+12% in the following five weeks) but decreases fatal pedestrian/bicyclist crashes (−24%), resulting in a near-neutral net effect on total fatal crashes (slight increase in occupant deaths offset by fewer pedestrian/cyclist deaths).
In summary, your memory is correct in that empirical data—particularly from U.S.-based studies—support an increase in traffic accident frequency (especially fatal crashes) associated with Daylight Saving Time variations, most reliably in the immediate aftermath of the spring transition due to sleep loss and misalignment. However, effects are not uniform across all studies, regions, or crash types, and some research highlights trade-offs (e.g., benefits to pedestrians from evening light). Debates continue regarding permanent DST, permanent Standard Time, or abolition of changes altogether, with organizations like the American Academy of Sleep Medicine favoring permanent Standard Time to minimize disruptions.