Alcohol, drugs, fatigue and fitness to drive
This domain tests whether you understand how alcohol, drugs, medicines, fatigue and illness degrade the skills driving depends on, and whether you can apply the arithmetic of elimination rather than the folklore of sobering up.
Alcohol
The legal limit in the region is low, commonly set at 0.5 g/l, with stricter or zero tolerance for novice and professional drivers. Impairment begins well below the limit: reaction time lengthens, attention narrows, confidence rises while skill falls, and night vision deteriorates. Alcohol is eliminated at roughly 0.1 to 0.15 g/l per hour, and nothing speeds that up. Coffee, cold air, a shower and food change how you feel, not how you test.
Drugs and medicines
Illegal drugs and many prescription medicines, including sedative antihistamines, tranquillisers and some painkillers, slow reaction and cause drowsiness. Read the label and ask the pharmacist; if the label warns against driving or operating machinery, do not drive.
Fatigue and fitness
Warning signs include yawning, heavy eyelids, drifting within the lane, missing signs and difficulty holding speed. The remedy is a short nap of 15 to 20 minutes, or stopping for the night, not the radio. Take a break at least every two hours, and be most careful between 2 and 5 am. Heat and dehydration in the dry season add to fatigue. Eyesight and any medical condition that could cause a sudden incapacity must be declared.
Worked example
A driver has three beers at 20:00 and drives at 22:00, feeling fine. Assuming roughly 0.6 g/l from those drinks and elimination of about 0.15 g/l per hour, the level at 22:00 is still near 0.3 g/l and falling slowly, with impairment present even where the reading is under the limit. The correct answer is not to drive. 'I feel fine' is the impairment talking.
Traps that cost marks
Believing coffee or a shower sobers you up; assuming the morning after is safe; treating a hangover as unrelated to driving; and ignoring a medicine label because the dose is small.