Background: A large proportion of fatal car accidents cannot be explained by traffic environment, technical defects or risk-taking behaviour. Driver impairment from disease, alcohol, drugs or suicidal impulses may be involved.
Material and method: Autopsy protocols from 167 car drivers involved in traffic accidents in Southeast Norway 1994-99 were reviewed retrospectively.
Results: In 89 of 135 deaths caused by trauma, there were no apparent explanations for the accident prior to autopsy. No differences were found with regard to signs of disease between drivers involved in unexplained and explained accidents. Drivers dead from trauma compared to drivers dead from natural causes had less often ischemic heart disease (p < 0.01). Blood alcohol level was above the statutory limit in 20% of drivers in both unexplained and explained accidents, and drugs were found in the blood in 27% of such cases. Only 13% of drivers in explained accidents collided with large motor vehicles, compared to 44% of the unexplained accidents.
Interpretation: Drivers with fatal injuries sustained in unexplained accidents seldom show signs of cardiac disease that could have contributed to the accident. It seems that such unexplained accidents are more often due to driving under the influence of alcohol or drugs, or to possible suicidal impulses.