Aims of the study: To determine the prevalence of alcohol or drug impairment in fatal road traffic crashes in Norway during 2005-2018, primarily among fatally injured motor vehicle drivers (including riders), and assess the degree of impairment and prevalence of problematic use of alcohol or drugs. Alcohol and drug impairment was studied in relation to age, sex, time and place of crash, type of motor vehicle, type of crash, and type of driving errors.
Methods: Data from the Crash Investigation Team Database operated by the Norwegian Public Roads Administration and forensic medicine data were used to obtain a comprehensive data set on killed drivers. Police data were used to generate statistics on killed and surviving road users involved in fatal crashes. Analytical findings of alcohol, illicit drugs and psychoactive medicinal drugs were assessed in relation to the legislative limits (corresponding to blood alcohol concentration (BAC) of 0.02 %) and limits for graded sanctions (corresponding to BAC of 0.05 % and 0.12 %) in the Road Traffic Act. Concentrations of alcohol or drugs in blood between BAC of 0.02 and 0.05 %, and corresponding values for drugs, indicate impairment in relation to the Road Traffic Act, but do not always indicate significant clinical impairment. Drivers with alcohol or drug concentrations corresponding to BAC of 0.05 % and higher, or high concentrations of amphetamines (5 times the legislative limits), were regarded as likely clinical impaired in this study.
Results: The Crash Investigation Team had recorded that 22 % of fatal road traffic crashes during 2005-2018 were related to alcohol or drug impairment. In those crashes, 546 road users were killed. The numbers of fatal crashes in related to population were highest in the northernmost and southernmost regions. The majority of the fatal crashes that happened during the night and early morning were related to alcohol or drug impairment. The prevalence of alcohol and drugs was higher among drivers killed in road departures than in collisions between two or more vehicles.
Of the killed car and van drivers, 66 % were investigated for alcohol or drug impairment by analysis of blood samples. Of those drivers, 35 % had concentrations of alcohol or drugs above the legislative limits given in the Road Traffic Act, 29 % had concentrations corresponding to BAC of 0.05 % or equivalent limits for drugs. Most of those drivers were significantly impaired, corresponding to a blood alcohol concentration of 0.12 % or more. A large proportion of those who were impaired by illicit drugs or psychoactive medicinal drugs had used two or more substances. The proportion of impaired drivers was higher among males than females, the highest proportion was observed among drivers below 40 years of age.
The proportion of alcohol impairment among killed car and van drivers declined during the study period, but no significant change was observed for drugs.
Information about alcohol and drug impairment that is not based on blood analysis is also recorded in the Crash Investigation Team Database. When combining those data with results from forensic testing, we estimated that at least 26 % of all killed car and van drivers were impaired by alcohol or drugs at the time of crash.
Among killed MC and moped riders, 64 % had been investigated for alcohol or drug impairment by analysis of blood samples. Of those riders, 26 % had concentrations of alcohol or drugs above the legislative limits; 22 % had concentrations above 0.05 % for alcohol or equivalent limits for drugs. A slightly larger proportion tested positive for illicit drugs than among killed car and van drives. When combining forensic data with data from the Crash Investigation Team Database we estimated that at least 18 % of all killed MC and moped riders were impaired by alcohol or drugs at the time of crash.
Among killed drivers of vans/lorries over 3500 kg, buses/minibuses and trucks, 7 % had concentrations of alcohol or drugs above the graded sanction limits corresponding to BAC of 0.05 %. Among drivers of other types of motor vehicles (ATVs, tractors, etc.), 31 % had concentrations of alcohol or drugs above those limits.
Alcohol or drug impaired drivers and riders killed in road traffic crashes had often been speeding and not used seatbelt or MC helmet. Impairment by alcohol or amphetamines was strongest associated with those driving errors. Impairment by medicinal drugs was associated with non-use of seatbelt, but not with speeding. It was more difficult to assess driving errors associated with cannabis impairment, as most of those who tested positive for cannabis had also used alcohol or other drugs at the same time, substances that were likely to contribute to driving errors.
Statistics from the police for the period 2016-2018 showed that few car and van drivers who were involved, but survived fatal crashes, were impaired by alcohol or drugs. Data also indicated that large proportions of killed bicycle riders and pedestrians were also impaired by alcohol or drugs corresponding to BAC of 0.05 % or more: 43 % of the bicyclists and 24 % of the pedestrians. However, those number may be inaccurate because few persons were included in the statistics. Among a total of 76 killed or surviving drivers of vans/lorries over 3500 kg, buses/minibuses and trucks, none were impaired.
Four out of five impaired drivers involved in fatal road traffic crashes had previously been convicted for criminal offences, almost half of them for drink or drug driving.
Conclusions: Test results from analysis of blood samples from drivers involved in fatal road traffic crashes indicate that the majority of those with alcohol or drug concentrations above the legislative limits had taken large doses or were multi drug users. This indicates problematic alcohol or drug use. The large proportion of drivers with previous convictions confirms this conclusion. It is important to take this fact into consideration when planning actions to reduce the prevalence of alcohol or drug impaired driving, as first time apprehension for drink or drug driving is a significant predictor for future impaired driving and involvement in road traffic crashes. The preventive effect of large fines, possible prison sentences, and suspension of the drivers’ license is insufficient. For this group of drivers, other preventive solutions must be used; both technical tools, training, and rehabilitation programmes may be used to change the drivers’ attitudes and behaviours.