The Lake House Party: 0.031, a Groggy Friend, and the Host
You host a birthday party at your lake house on Flathead Lake. Guests include your 20-year-old nephew and his friend, who is also 20 and has been asleep on the couch since 10 p.m. By 11:30 p.m. your nephew admits to two beers and blows 0.031 on a friend's portable breath tester. He insists on driving himself home: 18 miles, 12 of them on a two-lane highway. You are 38, have had three beers over about four hours, and weigh 170 pounds. You feel fine. Your nephew says 0.031 is 'way under the limit' and that the worst that can happen is a warning. The friend wakes up and offers to drive instead, though he looks groggy. The keys are on the kitchen counter.
1. Is your nephew legal to drive at 0.031? Explain the threshold that actually applies to him.
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He is wrong on the law. Montana sets a per se limit of 0.02 for drivers under 21, so 0.031 is over the line and can support a DUI charge even though it is far below the 0.08 limit used for adults. The 0.08 number applies to drivers 21 and older; for younger drivers the threshold is deliberately near zero. The portable tester is a screening device, not the evidentiary test, but a result over 0.02 is enough to establish probable cause for a blood or breath test. Beyond the charge, 0.03 in an inexperienced 20-year-old measurably slows reaction time and increases risk-taking on a dark two-lane road. He should not drive. The realistic answers are the couch, a rideshare, or a licensed driver who has not been drinking.
2. You have had three beers over four hours and feel fine. Should you drive, and how do you reason about it without a breath test?
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Feeling fine is not the test. A rough estimate: for a 170-pound man, each standard drink is worth roughly 0.02 BAC near peak, so three drinks spread over four hours, with elimination of about 0.015 per hour, probably puts you somewhere around 0.02 to 0.04 by 11:30 - under 0.08, but not zero. Montana does not require 0.08 to charge DUI; a driver can be convicted at a lower concentration with supporting evidence of impairment, and any alcohol degrades exactly the skills night driving on a two-lane road demands. Decide out loud that you are not driving tonight, before anyone asks. Also keep any open container in the house; carrying one into the vehicle would be its own violation.
3. The friend is sober but was just woken up. How does he rank among your options, and what is your exposure as the host?
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He is the best driving option, but only conditionally. 'Sober' matters less if he is genuinely licensed and insured, and 'groggy' is its own impairment: drowsy driving produces reaction times comparable to low-level alcohol, and he has been pulled out of deep sleep at 11:30 p.m. for an unfamiliar 18-mile drive. The ranking is therefore: everyone stays, then the groggy sober friend driving, then anyone with alcohol in them driving, which is not an option at all. Separately, you have exposure as the adult host. Furnishing alcohol to guests under 21, and knowingly allowing underage drinking on property you control, carry both criminal and civil consequences in Montana. Shutting the party down is the clean answer.