Most drivers are legally impaired at 0.08 BAC (Utah uses 0.05). Commercial drivers face a much stricter standard while operating a commercial motor vehicle.
The 0.04 limit
Federal rules prohibit operating a CMV with a BAC of 0.04 or higher. A violation is a major offense and carries at least a one year CDL disqualification.
Any detectable alcohol
Under 49 CFR 392.5, a driver found with any detectable alcohol while on duty, even below 0.04, is placed out of service for 24 hours. DOT testing rules treat a result between 0.02 and 0.039 the same way.
The four hour rule
Drivers may not consume alcohol within four hours before going on duty or operating a CMV, and may not carry alcohol in the vehicle unless it is part of a documented shipment.
How long alcohol stays in your system
On average your body clears roughly one standard drink per hour, but weight, food, sleep and medication change that. Coffee and cold showers do not speed it up. Many drivers carry a personal breathalyzer as a cautious check. See our breathalyzer guide, and remember a personal device is never a guarantee you are safe or legal to drive.
Check before you drive
SafetyFuel Cell Breathalyzer
A more accurate personal check than cheap sensor models. Useful for drivers held to a 0.04 limit and the four hour rule.
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SafetyBACtrack Breathalyzers
Popular consumer brand with fuel cell options and app connected models.
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SafetyBreathalyzer Mouthpieces
Keep extras in the cab so your device stays clean and ready.
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CommercialDUI.com is an independent information resource for commercial drivers. We are not a law firm and nothing on this site is legal advice. Laws change and vary by state, so confirm details with your state licensing agency or a licensed attorney.