US Legal Blood Alcohol Limits: BAC Thresholds for Drivers

Blood Alcohol Concentration (BAC) limits for driving in the United States are set at the state level but uniformly follow federal guidelines tied to highway funding.

Standard Limits

• Non-commercial drivers (≥21): 0.08% (80 mg/dL) — all 50 states, DC, Puerto Rico.
• Commercial drivers (CDL): 0.04% (40 mg/dL) — federal standard (FMCSA).
• Under 21 ("Zero Tolerance"): 0.00–0.02% (varies by state; any detectable in many).

Enhanced Penalties

• High BAC: ≥0.15% (many states) → aggravated DUI, mandatory jail, IID.
• Repeat offenses: Escalating penalties, felony thresholds.

Impairment Below Legal Limit

• Driving skills degrade at 0.02–0.05% (tracking, steering, reaction time).
• NTSB recommends 0.05% limit (adopted by Utah; under consideration elsewhere).
• Commercial pilots: 0.04% (FAA); 8-hour "bottle-to-throttle" rule.

Measurement

• Breathalyzer (evidentiary): converts breath alcohol to BAC estimate.
• Blood draw: gold standard; required for refusal in some states.
• Urine: less common, less correlated with impairment.

Key Takeaway

0.08% is a legal threshold, not a safety threshold. The only safe BAC for driving is 0.00%. Plan alternative transportation if consuming alcohol.