At-fault drivers in fatal crashes: A comparative study of alcohol and polysubstance use

This comprehensive register-based study examines fatal at-fault crashes of motor vehicle drivers with alcohol and other substance findings. We categorized substances with possible impact on driving into three categories: alcohol, medicines without addiction potential, and other substances, including illegal substances and medications with addiction potential. We analyzed the differences in crash circumstances and risk factors using odds ratios (ORs), comparing at-fault drivers with different substance combinations to those who were non-impaired.

Our material comprises crash data from the Finnish Road Accident (FRA) database in 2019-2022. Multidisciplinary Road Traffic Accident Investigation Teams (RAITs) investigate all fatal crashes in depth, and the Finnish Crash Data Institute (OTI) maintains the FRA database. RAITs have access to all police records, including medico-legal autopsy findings and toxicological data from virtually all deceased drivers.During the study period, there were 750 at-fault motor vehicle drivers of fatal crashes. Our final study material consisted of all data with information on alcohol and other substance findings, including 234 drivers with substance findings, and 446 non-impaired drivers.

Alcohol was clearly the most prevalent substance, used by 75% of the drivers with substance findings. The mean alcohol concentration in alcohol-only cases was 1.64‰, and in cases with alcohol and other substances, 1.45‰. Drivers with substance findings were much more likely to have prior DUI offenses (OR = 21.9 [10.6-45.0]). Moreover, drivers using substances other than alcohol had even higher odds of previous DUIs (OR = 31.9 [13.5-75.3]). Drivers with alcohol findings were more likely <25 years old compared to non-impaired drivers (OR = 2.10 [1.31-3.37]). Drivers with substance findings had higher odds of causing a crash while speeding compared to non-impaired drivers (for example, speeding at least 30 km/h: OR = 5.88 [4.00-8.62]). We found no statistically significant differences between drivers who had used alcohol alone and those who had used alcohol and other substances.

Alcohol with high concentrations dominated among at-fault drivers with substance findings in fatal road traffic crashes. Substance use co-occurred with other forms of risk taking such as speeding. Young drivers were overrepresented among drivers with alcohol findings. Despite new illegal substances and increasing drug use, alcohol still has a major impact on fatal crashes. This means that traditional measures for tackling DUI problems still apply but we must be open for new innovations, too.