Alcohol, Drugs, and Driver Responsibility
This domain covers impairment limits, implied consent, and the responsibilities that follow a crash or a violation. Montana enforces both a per se number and a broader "under the influence" standard.
Limits
- 21 and older: 0.08% BAC is the per se limit.
- Under 21: 0.02% - Montana's zero-tolerance law.
- Commercial drivers: 0.04%. You can still be convicted below the limit if your driving and behavior show impairment. The number is not a safe-driving threshold.
Implied consent and consequences
Getting a Montana license means consenting to a breath or blood test when an officer has reasonable grounds. Refusing brings a license suspension - one year for a first refusal - and the refusal can be used against you in court. A first DUI carries jail time, fines, license suspension, and mandatory alcohol assessment. An aggravated DUI, at 0.16% or above or with a child in the vehicle, brings tougher penalties.
Drugs, fatigue, and responsibility
Prescription and over-the-counter medications count: drowsy cold medicine, muscle relaxants, and anti-anxiety drugs all impair. Cannabis is legal for adults in Montana, but driving under its influence is still DUI. Fatigue is impairment too - after about 18 hours awake your reaction times resemble legal intoxication. You must stop and report any crash involving injury, death, or significant property damage, and leaving the scene of an injury crash is a serious crime.
Worked example
A driver with a 0.07% BAC is stopped after running a red light, slurring words, and failing the walk-and-turn test. He argues he is "under the limit." He can still be convicted: 0.08% defines the automatic case, but the state can prove impairment from driving behavior, field sobriety tests, and statements. The limit is a ceiling, not a license.
Traps that cost marks
Believing coffee, a cold shower, or food sobers you up (only time does, roughly one standard drink per hour); assuming a prescription label means you can drive; thinking a first offense is just a fine.