How does sleep inertia affect driving?
Significantly. Right after waking, reaction time, attention and decision-making are impaired; in one study, performance on an addition test just after waking was worse than after a full night without sleep. If you can, wait at least 15–30 minutes before driving, especially after short or broken sleep.
The evidence
Driving safely needs situational awareness, information processing, decision-making, memory and quick reactions, and sleep inertia affects these capacities (Hilditch & McHill, 2019). In one study, performance on an addition test immediately after waking was significantly worse than after one night of sleep deprivation (Wertz et al., 2006).
Worst combinations
Sleep inertia is stronger when you are woken from deep (slow-wave) sleep and after sleep loss (Tassi & Muzet, 2000). That is the typical situation of on-call workers and early-shift drivers who are woken suddenly and have to leave right away.
Protective tactic
Give yourself at least 15–30 minutes between waking and driving: the worst of sleep inertia is usually in that window, and without major sleep loss it rarely lasts beyond 30 minutes (Tassi & Muzet, 2000). Use the time to get up, get some light and have your coffee, which takes a while to kick in.
Sources
- Hilditch & McHill, Nature and Science of Sleep, 2019. Sleep inertia: current insights
- Wertz et al., JAMA, 2006. Effects of sleep inertia on cognition
- Tassi & Muzet, Sleep Medicine Reviews, 2000. Sleep inertia
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