Alcohol, Drugs, Fatigue and Fitness to Drive
What this domain tests
This domain tests the legal limits, how impairment affects a heavy-vehicle driver, and the honest limits of "sobering up" tricks.
Legal limits in South Africa
- Ordinary drivers: 0,05 g per 100 ml of blood, or 0,24 mg per 1 000 ml of breath.
- Professional drivers holding a PrDP: 0,02 g per 100 ml of blood, or 0,10 mg per 1 000 ml of breath. Refusing to give a breath or blood sample is itself an offence. A PrDP also depends on a valid medical certificate covering eyesight and general fitness.
Impairment and elimination
Alcohol slows reaction time, narrows attention and creates false confidence - exactly the skills a loaded truck demands. The body eliminates alcohol at roughly one unit per hour, and nothing speeds that up; coffee, cold showers and food only make an impaired driver feel more awake.
Fatigue
Warning signs include yawning, heavy eyelids, drifting, missed signs, irritability and micro-sleeps. The countermeasures are sleep and a break, not the radio or an energy drink. Plan breaks, avoid the small hours, and never start a long trip straight after a full shift.
Worked example
A PrDP driver has two beers at lunch and feels fine four hours later. Reasoning: his limit is 0,02 g/100 ml, a quarter of the ordinary limit, so a small intake can still leave him over the threshold, and feeling fine proves nothing. Action: he does not drive.
Traps
Applying the 0,05 limit to a PrDP holder; assuming a nap cancels alcohol; taking medication labelled "may cause drowsiness" before a shift.