The impact on alcohol-related collisions of the partial decriminalization of impaired driving in British Columbia, Canada

•This study evaluates the impact of new laws in British Columbia, Canada, designed to reduce alcohol-related collisions.•The laws increased the efficiency for processing drinking drivers if offenders were not charged under the Criminal Code.•Canadian Criminal Code charges declined 68.2% resulting in partial decriminalization of drinking and driving.•The intervention was associated with significant reductions in three types of alcohol-related collisions.•Provincial laws for drinking drivers can be more efficient and effective than Canadian laws in reducing collisions. The purpose of this paper is to assess the impact of administrative sanctions introduced as part of a new law for drinking drivers in British Columbia, Canada. The new law, known as immediate roadside prohibitions (IRP), aimed to increase the efficiency of police and courts for processing drinking drivers, thereby increasing the certainty of their being apprehended and punished. However, in order to maintain these efficiencies, sanctions under this new law largely replaced laws under the Criminal Code of Canada for Driving While Impaired (DWI) by alcohol, which had more severe penalties but lower certainty of punishment. We examined whether the intervention was related to abrupt significant declines in three types of alcohol-related collisions (i.e. fatalities, injuries or property damage only) compared to the same type of collisions without alcohol involvement. An interrupted time series design, with a non-equivalent control was used, testing for an intervention effect. Monthly rates of the three types of collisions with and without alcohol involvement were calculated for the 15-year period before and the 1-year period after implementation of the new law. ARIMA time series analysis was conducted controlling for trend effects, seasonality, autocorrelation, and collisions without alcohol. Significant average declines (p