The aim of the study was to explore the severity of injuries sustained by the driver and passengers of a vehicle involved in a fatal crash, based on the risks posed by the traffic system, and to evaluate the scope for preventing road traffic casualties. The study was based on detailed data of multidisciplinary accident investigations of 422 fatal motor vehicle accidents where 524 victims died on two-lane main roads during the years 1996­2003 in Finland. Accidents due to alcohol, failure to wear seatbelts and speeding were filtered out, as were those due to sickness or categorized as suicidal. Of all victims 58% died as a result of head-on collisions. The probability of dying in a head-on collision began to grow when the speed change (v) in the accident exceeded 40 km/h. The study also revealed high death rates (>50%) when the v reached 80 km/h. The results support either the installation of median barriers on two-lane main roads with a speed limit of 80 km/h or higher, or switching to a 70 km/h speed limit.