Sleep and road safety are inseparable. Even one short night increases crash risk, and micro-sleep can strike without warning. This guide explains how to detect fatigue, plan rest and apply countermeasures before you start the engine.
Sleep debt and reaction time
| Sleep last 24 h | Reaction time | Estimated crash risk |
|---|---|---|
| 8 hours | Baseline | Reference |
| 6 hours | +20% | 1.3x |
| 5 hours | +40% | 1.9x |
| 4 hours or less | +70% | 2.8x |
| The figures are based on international fatigue studies used by the Norwegian Public Roads Administration. Read more about human limitations in Humans in traffic. |
Warning signs of dangerous fatigue
- You forget the last kilometres or have to reread wayfinding signs
- You blink slowly, yawn frequently or feel your head nodding forward
- You react late to speed and following distance or need sudden corrections
- You notice mood swings or irritation over small incidents
- You experience micro-sleep: brief losses of awareness with your gaze off the road
If you continue driving, micro-sleep can lead to severe run-off-road crashes. Also read Fitness to drive.
Plan rest before the trip
- Aim for at least seven hours of sleep before longer trips.
- Start driving when you are normally awake; avoid departures between 02:00 and 05:00.
- Share driving duties with a companion whenever possible.
- Record sleep and breaks in your logbook to document habits.
- Combine the rest plan with the checklist in Preparing for a long trip.
Countermeasures while driving
- Take planned breaks at least every two hours, more often at night
- Apply defensive driving with larger safety margins, see Defensive driving
- Split the journey into stages and log each stop with time and location
- Avoid heavy meals and sugar spikes that trigger energy crashes
- Use fresh air or climate adjustments only as short-term aids
- Switch drivers when you feel the symptoms above, or take a 20-minute nap before continuing
High-risk periods during the day
| Time of day | Body state | Recommendation |
|---|---|---|
| 02:00–05:00 | Circadian minimum | Avoid driving or schedule extended rest |
| 13:00–15:00 | Natural energy dip | Add a break and light meal |
| After 9 hours awake | Accumulated sleep pressure | Arrange a driver change or overnight stop |
Combine sleep and technology
- Activate drowsiness alert in modern cars and learn the warning symbols, see Vehicle safety equipment
- Use sleep tracking apps as a reminder, but rely on honest self-assessment
- Plan navigation routes with built-in break suggestions as described in Motorway driving
Legal obligations
Section 21 of the Road Traffic Act requires the driver to be fit to drive. Fatigued driving can be considered negligent and lead to fines or loss of licence, see Sanctions: fines, confiscation, liens and points. Coordinate your sleep strategy with the rules on Sobriety requirement to control all risk factors.
Build a sleep plan
- Keep a weekly sleep log with consistent bedtimes and wake-up times.
- Adjust bedtime gradually (15 minutes per day) if you must drive early.
- Prepare a dark bedroom and put away screens an hour before sleep.
- Set up a backup plan: inform a companion or family member for night driving.
- Review each trip to evaluate which measures worked and update the log.