Four beers, three hours of sleep and a hay-fever tablet
Marko is 26, weighs 78 kg and holds a full A2 licence. On a Friday night he drinks four 0.5-litre beers at 5% alcohol between 23:00 and 03:00. He gets about three and a half hours of broken sleep, wakes at 07:00 with a dry mouth and itchy eyes, and takes a cetirizine tablet. The packet carries a drowsiness warning and states that the medicine may affect the ability to drive or operate machinery. He feels 'fine, just tired'. He must be at work at 08:00, 9 km away, and his only other option is a bus that takes 35 minutes. The legal limit in North Macedonia is 0.5 g/L of alcohol in blood. His bike is in good order and it is a dry, bright morning.
1. Estimate his blood alcohol at 07:30 and decide whether he may ride.
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Do the rough arithmetic. Four beers of 500 ml at 5% contain about 100 ml of pure alcohol, roughly 79 g. Using a Widmark factor of about 0.7 for a 78 kg man, the peak concentration would be around 79 ÷ (78 × 0.7) ≈ 1.4 g/L. Elimination runs at roughly 0.15 g/L per hour once absorption is finished, so from about 04:00 to 07:30 - three and a half hours - he clears around 0.5 g/L. That leaves roughly 0.9 g/L, well above the 0.5 g/L limit.
The estimate has wide error bars, but every reasonable assumption puts him at or above the limit. Feeling fine is not evidence: tolerance changes how you feel, not how impaired you are. He must not ride, and 'sleeping it off' for a few hours is not a plan for 07:30.
2. Even if his alcohol were zero, why is the cetirizine plus the short sleep a separate problem?
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Alcohol, sleep loss and sedating medicines all depress the same system, and their effects add rather than replace each other. Cetirizine is a second-generation antihistamine but it is still sedating in a meaningful proportion of users, which is why the leaflet warns about driving and machinery.
After three and a half hours of sleep he is already carrying a sleep debt: reaction time lengthens, attention lapses and microsleeps become possible - on a motorcycle, a two-second lapse at 50 km/h is nearly 30 m of blind travel. Adding a sedating tablet on top of a hangover produces a rider who is impaired in a way no breathalyser will detect.
The legal test is not the only test. A rider who is below the limit but cannot hold a steady line, or who yawns and loses focus, is still unfit to ride and can be treated as such if stopped or after a crash.
3. What should he actually do, and what are the realistic consequences if he rides anyway?
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Take the bus, a taxi, or call a colleague; leave the bike parked legally at home. The 35-minute bus ride is the cheap option. He should also not drive a car, since the same impairment applies, and he should tell his employer if the drowsiness makes safety-critical work unsafe.
If he rides and is stopped, the alcohol reading is the evidence, not his opinion; a reading above the limit brings a fine, penalty points and a driving ban, and the ban applies to the motorcycle licence he depends on. If he crashes, the insurer will examine the alcohol and medicine findings, and cover can be refused or reclaimed, leaving him personally liable for damage and injury to others. The arithmetic above shows that at 07:30 the risk is not theoretical.