Haghpanahan H, et al. - Authors assessed the impacts of lowering blood alcohol concentration (BAC) limits for drivers on road traffic accidents (RTAs) and alcohol consumption. Findings did not suggest the association of lowering the driving BAC limit to 0·05 g/dL from 0·08 g/dL in Scotland with a reduction in RTAs, but this change was related to a small reduction in per-capita alcohol consumption from on-trade alcohol sales. The legislative change was not suitably enforced—for example with random breath testing measures- is one plausible explanation. RTA outcomes were not seen to improve by changing the legal BAC limit for drivers in isolation. They noted internationally significant policy implications of these findings as several countries and jurisdictions consider a similar reduction in the BAC limit for drivers.

• Experts conducted a natural experiment in which they used an observational, comparative interrupted time-series design by use of data on RTAs and alcohol consumption in Scotland (the interventional group) and England and Wales (the control group).
• They obtained weekly counts of RTAs from police accident records and estimated weekly off-trade (eg, in supermarkets and convenience stores) and 4-weekly on-trade (eg, in bars and restaurants) alcohol consumption from market research data.
• They also used data from automated traffic counters as denominators to calculate RTA rates.
• They assessed the impact of the intervention on RTAs by use of negative binomial panel regression and on alcohol consumption outcomes by use of seasonal autoregressive integrated moving average models.
• Weekly rates of RTAs in Scotland, England, and Wales were the primary outcomes.

• As per data, the evaluated the weekly rate of RTAs and alcohol consumption between Jan 1, 2013, and Dec 31, 2016, before and after the BAC limit came into effect on Dec 5, 2014.
• Findings suggested that after the reduction in BAC limits for drivers in Scotland, no significant change were found in weekly RTA rates after adjustment for seasonality and underlying temporal trend (rate ratio 1.01, 95% CI 0.94–1.08; p=0.77) or after adjustment for seasonality, the underlying temporal trend, and the driver characteristics of age, sex, and socioeconomic deprivation (1.00, 0.96–1.06; p=0.73).
• Results demonstrated that relative to RTAs in England and Wales, where the reduction in BAC limit for drivers did not occur, a 7% increase in weekly RTA rates in Scotland after this reduction in BAC limit for drivers was noted (1.07, 1.02–1.13; p=0.007 in the fully-adjusted model).
• For serious or fatal RTAs and single-vehicle night-time RTAs, similar findings were observed.
• They noted an association of the change in legislation in Scotland with no change in alcohol consumption, measured by per-capita off-trade sales (−0.3%, −1.7 to 1.1; p=0.71), but a 0.7% decrease in alcohol consumption measured by per-capita on-trade sales (−0.7%, −0.8 to −0.5; p < 0.0001).