How Tired is Too Tired to Drive? Systematic Review
Summary
This systematic review analyzed 61 studies on how prior sleep duration affects driving safety. The evidence shows clear thresholds: after 6–7 hours of sleep, drivers already face about a 30% higher crash risk compared with being fully rested (≥8 hours). With only 4–5 hours of sleep, driving performance drops sharply and crash risk nearly doubles. Below 5 hours, the risk is consistently high. These findings support the idea that fatigue could be treated like alcohol, with a minimum “sleep requirement” for safe driving.
Why It Matters For Night Shift Workers and Night Owls
For shift workers, the danger is not just staying awake for long hours—it’s also how much sleep you’ve had before getting behind the wheel. This review shows that even 6–7 hours of sleep may leave you impaired, and fewer than 5 hours makes driving especially risky. For night-shift workers heading home, that means protecting your sleep is just as important as the work itself. Planning for enough rest, or arranging alternatives if sleep has been short, can make the difference between a safe trip and a dangerous one.
Notes
Includes nurses’ naturalistic driving study.