The driver's condition
Understanding how fatigue, stress, eyesight and medical conditions affect your ability to drive safely.
Updated 13 June 2026
Eyesight: a vital sense for driving
Driving relies 90% on vision. To obtain or keep your licence, you must have a visual acuity of at least 5/10 for both eyes combined. If your eyesight does not meet this standard, wearing glasses or contact lenses becomes compulsory. This requirement will be noted on your licence and you must always carry a spare pair in the vehicle.
If one eye has an acuity below 1/10, the other must reach at least 5/10. Colour blindness, however, is not an obstacle to driving.
Road signs are designed to be legible based on the speed being driven, not the surrounding scenery. That is why they are twice as large outside built-up areas as in town. With 10/10 acuity, you can spot them at about 150 m on open roads and 50 m in built-up areas. Always look well ahead to anticipate hazards and maintain a steady course.
Field of vision and speed
At a standstill, your field of vision covers roughly 180 degrees. But the faster you go, the narrower it becomes: at 130 km/h it shrinks to about 30 degrees, creating a 'tunnel vision' effect. You only perceive the centre of the road and lose sight of things on the sides, such as pedestrians and vehicles.
At high speed, the brain can no longer process all the information. Peripheral cues are overlooked, which considerably increases the risk of failing to detect a hazard.
Vision has two complementary components. Peripheral vision (180 degrees at a standstill) detects movement and contrasts across a wide field, while central vision, which is more precise, analyses the details of what the eye has spotted. At high speed, peripheral vision is sacrificed, preventing the detection of pedestrians, two-wheelers or vehicles approaching from the side.
To compensate for the loss of field of vision at high speed, scan the road regularly instead of staring at a single point. Look well ahead to anticipate, then check your mirrors and the sides of the road.
Fatigue: the silent enemy
Driving places intense demands on both body and mind: visual, nervous and muscular fatigue. Fatigue is responsible for roughly 20% of fatal road accidents. On motorways, one fatal accident in three is caused by falling asleep at the wheel.
The causes of fatigue are varied. They may come from the environment (night driving, blinding sun, monotonous traffic), from the driver (lack of sleep, stress, hunger) or from the vehicle (noise, discomfort, excessive heat).
Drowsiness multiplies the risk of an accident by 8. The most dangerous periods are between 2 a.m. and 5 a.m., and between 2 p.m. and 4 p.m.
Watch for the first signs: repeated yawning, stiffness in the neck, stinging eyes, difficulty keeping your lane, heavy eyelids. As soon as these signals appear, do not fight it — pull over.
Good habits to combat fatigue
Getting a good rest before a long journey is the best prevention. During the trip, take a break of at least 15 to 20 minutes every 2 hours. Stay hydrated and eat balanced meals. If possible, take turns driving and do not exceed 8 hours of driving in a day.
Never set yourself an arrival time: it unconsciously pushes you to drive faster or postpone breaks. Opt for a 15 to 20-minute nap at a rest area as soon as fatigue sets in.
Stress and emotions
Stress, irritation or impatience degrade the quality of your driving. They cause a lack of attention, irritability towards other road users and slower reflexes. A stressed driver tends to take reckless risks: sudden acceleration, failure to maintain safe distances, dangerous overtaking. Speed itself generates stress: the brain must process a greater flow of information, leading to rapid visual and psychological fatigue.
If you feel anger or frustration rising, do not react impulsively. Breathe calmly, loosen your grip on the steering wheel and, if necessary, take a break to regain your composure.
Medical conditions incompatible with driving
Certain medical conditions require regular check-ups with a doctor approved by the prefecture in order to continue driving. These include high blood pressure (risk of heart attack or stroke), severe diabetes (cardiovascular risk) and epilepsy (risk of sudden loss of consciousness).
Only a doctor approved by the prefecture can authorise or prohibit you from driving in the case of an incompatible condition. If you lose the use of a limb, a vehicle adaptation may be prescribed, but you may not modify it yourself.
A final point often asked in the exam: pregnant women must wear a seatbelt. Only a medical prescription can exempt them, and they must present it if stopped.
Recap
- The minimum visual acuity required for driving is 5/10 for both eyes.
- The field of vision goes from 180 degrees at a standstill to roughly 30 degrees at 130 km/h (tunnel vision).
- Fatigue is responsible for roughly 20% of fatal accidents; on motorways, 1 in 3 fatal accidents is caused by falling asleep.
- Drowsiness multiplies the risk of an accident by 8.
- Take a 15 to 20-minute break every 2 hours and do not exceed 8 hours of driving per day.
- Stress and irritation reduce attention and reflexes at the wheel.
- High blood pressure, severe diabetes and epilepsy require an approved medical opinion to drive.
- Pregnant women must wear a seatbelt, unless exempted by a medical prescription.
Test yourself
What is the minimum visual acuity required for driving (both eyes combined)?
- ○10/10
- ✓5/10
- ○3/10
- ○7/10
Correct answer : 5/10
On motorways, what proportion of fatal accidents is caused by falling asleep at the wheel?
- ✓1 in 3
- ○1 in 5
- ○1 in 10
- ○1 in 2
Correct answer : 1 in 3
Sources: Sécurité routière (securite-routiere.gouv.fr) and service-public.fr.