Alcohol, drugs, fatigue and fitness to drive
Domain 6: Alcohol, drugs, fatigue and fitness to drive
Questions test the legal limits, how alcohol and drugs actually affect driving, and whether you can recognise when you or a passenger should not be behind the wheel.
Legal limits (South Africa)
- Ordinary drivers: 0.05 g per 100 ml of blood, or 0.24 mg per 1 000 ml of breath.
- Professional drivers (PrDP holders): 0.02 g per 100 ml. Refusing a blood or breath sample is an offence and carries the same consequences as driving over the limit.
What alcohol does
Alcohol is a depressant. It slows reaction time, narrows attention, impairs distance judgement and balance, and raises confidence - the combination that produces single-vehicle crashes at night. It is eliminated at roughly 0.01–0.02 g/100 ml per hour. Nothing speeds this up: coffee, cold showers and food only make a drunk driver feel more alert.
Drugs and medication
Cannabis, stimulants, prescription sedatives and antihistamines all impair driving, and combining them with alcohol multiplies the effect. Read the label, ask the pharmacist, and do not drive if the medicine warns against it.
Fatigue
Warning signs: yawning, heavy eyelids, drifting within the lane, missing signs or exits, and not remembering the last few kilometres. Countermeasures: stop and rest for 15–20 minutes, sleep if possible, share the driving, and avoid long stretches between 02:00 and 06:00 when alertness is naturally lowest. Break at least every two hours. Opening a window or turning up the radio does not reverse fatigue.
Fitness
Your eyesight, hearing and general health must meet the standard; report epilepsy, diabetes, blackouts or heart conditions that could cause sudden incapacity, and do not drive when feverish or exhausted.
Worked example
A driver stops drinking at 22:00 with a blood alcohol level of about 0.08 g/100 ml. Reasoning: at roughly 0.015 g/100 ml per hour he needs about two hours just to reach the legal limit - and he remains impaired. Driving at 23:00 is an offence.
Traps
Believing coffee sobers you; assuming a small beer keeps you "under the limit"; treating a hangover as fit to drive.