People who wake early yet feel a surge of fatigue in the afternoon show a reduced ability to drive later in the day. This pattern shows up in a published study from the International Journal of Human Factors and Ergonomics (IJHFE). The researchers measured how driving performance shifts as the day progresses for those who consider themselves morning-oriented. The core finding: the afternoon slump is linked not to the act of driving itself, but to a dip in alertness and slower reactions that emerges after lunch. The study highlights that fatigue after meals can blunt the quickness and attentiveness drivers need to navigate roads safely, even for individuals who start their day early. [Citation: International Journal of Human Factors and Ergonomics]
The experimental setup involved twelve male participants who identified as early risers. Each participant completed a series of driving tasks at two times: before lunch and after lunch. The tasks were designed to simulate real-world driving demands, including speed control, lane maintenance, and hazard recognition. Across the board, the post-lunch period brought noticeable declines in performance metrics. Reaction times lengthened, decision speed slowed, and overall vigilance dipped compared with the pre-lunch measures. The participants themselves reported feeling more fatigued after the midday meal, aligning subjective experience with objective performance data. [Citation: International Journal of Human Factors and Ergonomics]
When interpreting these results, the researchers point to the body’s natural circadian rhythm as a possible driver of the observed effects. People who favor early rising may experience a different internal clock alignment, which could make the afternoon period a more challenging time for tasks requiring sustained attention, such as driving. Importantly, the study finds that the time of day exerts a stronger influence on performance than the order in which the driving tasks were performed. In other words, afternoon fatigue appears to be the dominant factor affecting driving ability in this group. [Citation: International Journal of Human Factors and Ergonomics]
From a broader perspective, the findings urge researchers and policymakers to consider chronotype alongside clock time when modeling how drivers behave on the road. Incorporating chronobiology into theoretical models could inform targeted safety recommendations, such as scheduling considerations for high-demand driving periods, or designing alert mechanisms within vehicles to counteract midday drowsiness. By acknowledging individual differences in circadian timing,Safety measures can be better aligned with real-world driving patterns, potentially reducing accident risk during the afternoon hours for morning-oriented individuals. [Citation: International Journal of Human Factors and Ergonomics]
Beyond the specifics of this study, the overarching takeaway is clear: the interplay between internal clocks and daily schedules matters for road safety. While afternoon fatigue is a common challenge, recognizing that chronotype shapes vulnerability can lead to practical strategies. Employers and transportation planners might explore staggered shifts, rest breaks, or in-vehicle fatigue monitoring to help drivers stay alert during peak risk periods. The research also invites further investigations into how meals, sleep quality, and caffeine consumption interact with circadian timing to influence driving performance across diverse populations. [Citation: International Journal of Human Factors and Ergonomics]
Overall, the evidence underscores a simple truth: time of day and personal biological timing jointly influence driving performance. Early risers are not uniformly immune to post-lunch impairment, but the degree of difficulty appears linked to the alignment between their internal clock and the external schedule. As science continues to unpack these connections, practical road safety measures stand to gain from this chronotype-aware perspective, potentially reducing the number of mishaps on afternoon drives. [Citation: International Journal of Human Factors and Ergonomics]
Scientists also note that this line of inquiry could yield quick, actionable steps. In three minutes, a brain function boost is possible for some individuals, offering a non-pharmacological approach to sustaining alertness during drivers’ midday tasks. While not a universal remedy, simple, science-informed strategies may help bridge the gap between morning vigor and afternoon fatigue, supporting safer driving outcomes for people with early chronotypes. [Citation: International Journal of Human Factors and Ergonomics]