Official blame for drivers with very low blood alcohol content: there is no safe combination of drinking and driving.

Background: Some laboratory studies find that driving is impaired even at blood alcohol content (BAC)=0.01%. However, no real-world traffic studies have investigated whether minimally 'buzzed' drivers (BAC=0.01%) are more likely to be blamed for a crash than are the sober drivers they collide with.

Purpose: To determine whether official blame for a crash increases significantly at BAC=0.01%.

Methods: We examined the relationship between the driver's BAC and the degree to which he or she was assigned sole official blame (SOB) for the crash. We analysed an official, exhaustive, nationwide US database (Fatality Analysis Reporting System; n=570 731), covering 1994-2011.

Results: Even minimally 'buzzed' drivers are 46% (24-72%) more likely to be officially blamed for a crash than are the sober drivers they collide with (χ(2)=20.45; p=0.000006). There is no threshold effect-no sudden transition from blameless to blamed drivers at BAC=0.08% (the US legal limit). Instead, SOB increases smoothly and strongly with BAC (r=0.98 (0.96-0.99) for male drivers, p<0.000001; r=0.99 (0.97-0.99) for female drivers, p<0.000001). This near-linear SOB-to-BAC relationship begins at BAC=0.01% and ends around BAC=0.24%. Our findings persist after controlling for many confounding variables.

Conclusions: There appears to be no safe combination of drinking and driving-even minimally 'buzzed' drivers pose increased risk to themselves and to others. Concerns about drunk driving should also be extended to 'buzzed' driving. US legislators should reduce the legal BAC limit, perhaps to 0.05%, as in most European countries. Lowering the legal BAC limit is likely to reduce injuries and save lives.