The purpose of this monograph is to describe trends in the interior safety of cars in terms of the frequency and severity of injuries among the car occupants, especially the drivers. Special references are made to the Influence of the weight of the car, the starting year of production of the car, and some safety devices such as safety belts and head rest fittings. The material comprises all accident-involved private cars reported to an insurance company during a five-year period. The total number of such cars was 339,675 in which 8,592 drivers and 5,469 passengers were injured or killed. This represents approximately one-fourth of all accident-involved cars reported to insurance companies during a five-year period in Sweden. Data which are normally stored in the insurance files have been supplemented with data concerning car weight and starting year of production of the cars. In injury-producing accidents hospital records and doctor's certificates were available in the majority of cases, as well as reports from the police investigations. All data were computerised. An additive regression model, was used to determine the influence of car weight, starting year of production of the car model, age of the car, safety belt usage and fitting of head rests, on the frequency of injuries.

Data concerning car occupants with permanent medical disability and financial disability were specially investigated to gain information on what type of injuries lead to major problems in later years.

A sample of car occupants with head injuries was investigated to study the frequency of problems remaining in later years.

The main conclusions reached are that the weight of the striking car as well as of the struck car influences the injury frequency and severity of injuries among drivers. The knowledge of impact biomechanics accumulated since the middle of the sixties seems to have improved the interior safety of cars. The results of the regression analysis implied that some of the small new cars have the same safety level as large old ones. Safety-belt usage diminishes the severity .of injuries and the risk of fatalities and it is proposed that the use of safety belts should also be compulsory in the rear seat.

Head rests prevent neck injuries in rear-end collisions in about one-fourth of the cases. Fixed head rests are more effective than adjustable ones. It is proposed that the fitting of head rests be made compulsory for all seating positions and that the head rests be improved further.

Slight head and neck injuries often lead to permanent disability and objectives for further studies of this problem are suggested.