The relationship between serious injury and blood alcohol concentration (BAC) in fatal motor vehicle accidents: BAC = 0.01% is associated with significantly more dangerous accidents than BAC = 0.00%.

Aim: To analyze the severity of automotive injuries associated with blood alcohol concentration (BAC) in increments of 0.01%.

Design/setting: Epidemiological study using the Fatality Analysis Reporting System.

Participants: All people in US fatal automotive accidents, 1994-2008 (n = 1 495 667).

Measurements: The ratio of serious: non-serious injuries for drivers, by BAC.

Findings: Accident severity increases significantly even when the driver is merely 'buzzed', a finding that persists after standardization for various confounding factors. Three mechanisms mediate between buzzed driving and high accident severity: compared to sober drivers, buzzed drivers are significantly more likely to speed, to be improperly seatbelted and to drive the striking vehicle. In addition, there is a strong 'dose-response' relationship for all three factors in relation to accident severity (e.g. the greater the BAC, the greater the average speed of the driver and the greater the severity of the accident).

Conclusions: The severity of life-threatening motor vehicle accidents increases significantly at blood alcohol concentrations (BACs) far lower than the current US limit of 0.08%. Lowering the legal limit could save lives, prevent serious injuries and reduce financial and social costs associated with motor vehicle accidents.