After the wedding: two beers and a checkpoint
It is 23:30 on a Saturday. You weigh about 70 kg and have been at a wedding since 19:00. You drank two 375 ml cans of 5% beer between 20:00 and 22:00 and ate a plate of food at 21:00. You feel alert. You have an 8 km drive home along the main road; the last 2 km are unlit and have pedestrians walking home from the same event. You are tired after a long week and your eyes feel dry. A police checkpoint is sometimes set up near the airport turn-off. Your cousin, who has not drunk, is at the wedding but lives in the opposite direction and would have to detour 20 minutes. Your car is parked on the road shoulder without lights.
1. Estimate whether you are likely to be under or over a typical legal alcohol limit, and explain why the estimate is not a safe basis for driving.
Read the worked answer
Do the arithmetic as a warning, not a permission. Two 375 ml cans at 5% contain about 30 g of pure alcohol. For a 70 kg man, a rough Widmark estimate gives a peak blood alcohol around 0.06 g/100 mL, or 60 mg/100 mL, though body composition, food and timing shift it. Food slows absorption but does not lower the total. Two hours after the last drink you may be near the peak or starting to fall; alcohol is eliminated at only about 10–15 mg/100 mL per hour. That could be around or above a 50 mg/100 mL limit and below an 80 mg/100 mL limit, but you cannot know which side of the line you are on. The estimate is not a defence: impairment, divided attention and night driving matter even below the limit. The safe answer is not to drive.
2. What alternatives should you use, and what should you do about the car?
Read the worked answer
Call the cousin first. A 20-minute detour is a small price; ask him to drive you and the car home, or to collect you. If he cannot, use a taxi or stay at the venue and retrieve the car in daylight. Do not sleep in the car on the road shoulder; it is unlit and other drivers may not see you. If you leave the car, park it legally, lock it, take the keys, and arrange collection the next day. Do not ask another guest who has been drinking. The decision has to be made before you start the engine, not at the checkpoint.
3. How do fatigue and the unlit pedestrians change the risk?
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Fatigue and alcohol are multiplicative, not additive. You have had a long week, dry eyes and a late night; that means slower reactions, poorer scanning and a real risk of a microsleep on an 8 km drive. The last 2 km are unlit and have pedestrians in dark clothing. At 40 km/h you need roughly 20 m to stop in good conditions, and at night your low beam may light only 30–40 m; a pedestrian at the edge may appear with no margin. Alcohol makes you less likely to notice them and more confident that you have. The combination is exactly the profile of a fatal pedestrian collision, so the only defensible plan is a sober driver.