A 6 A.M. Ride After Beer, Cannabis, and Poor Sleep
Marcus, 34 and 190 pounds, spent Saturday evening at a friend's house. Between 7 p.m. and 11 p.m. he drank four 16-ounce craft beers at 7% alcohol by volume. He also smoked cannabis around 10 p.m. He took a 10 mg cetirizine tablet for allergies at 11:30 p.m. He slept about four hours and wakes at 6 a.m. feeling “a little groggy but fine.” He plans to ride his motorcycle 25 miles to work at 6:30 a.m. He has eaten breakfast and had one cup of coffee. The weather is dry and traffic is light. He says he has “slept it off” and that coffee will “straighten him out.” He has no prior DUI.
1. Estimate Marcus's impairment and decide whether he should ride. Show your reasoning.
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He should not ride. Four 16-ounce beers at 7% contain about 4.5 ounces of pure alcohol, or roughly 7.5 standard drinks. For a 190-pound man, a rough Widmark estimate puts peak BAC near 0.18%. Seven hours after the last drink, with elimination around 0.015% per hour, he could still be near or above 0.08%, depending on timing, food, and metabolism. That estimate is not precise enough to certify him under the limit. More importantly, he also used cannabis, took a sedating antihistamine, and slept only four hours. Those combine to slow reactions, reduce attention, and increase drowsiness even if his BAC has fallen. Coffee does not speed alcohol elimination and does not reverse cannabis or antihistamine effects. The safe decision is not to ride; he should use another driver, public transit, or delay the trip.
2. What if he waits two hours, drinks more coffee, and takes a shower? Does that make him safe to ride?
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No. Two hours adds only about 0.03% of alcohol elimination, which may not be enough if he is near or above 0.08%, and it does nothing for cannabis or cetirizine. Coffee and a shower can make him feel more alert, but feeling alert is not the same as being fit to ride. Cannabis effects can include slowed reaction time, altered time perception, and impaired lane tracking, and combining it with alcohol increases impairment more than either alone. Cetirizine can cause drowsiness, especially with only four hours of sleep. He should not use a “feels fine” test. If he wants to ride later, he should wait much longer, sleep, and reassess without any impairing substances; even then, he should not ride if he is still drowsy.
3. How should the law treat his situation, and what is the safest plan?
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North Dakota prohibits driving under the influence of alcohol, drugs, or a combination. A BAC of 0.08% or more is a per se violation, but a driver can also be convicted for being under the influence at a lower BAC or from drugs. “Actual physical control” can apply even if the motorcycle is not moving, so sitting on it with the engine running is risky. The safest plan is to leave the motorcycle at home, arrange a ride, or use a ride service. He should not “test” himself by riding around the block. If he must retrieve the bike later, he should do so after a long interval, with no alcohol or cannabis on board, and with adequate sleep. He should also recognize that a DUI affects his license, insurance, and employment; the cost of a ride is trivial compared with that risk.