The movement of cars striking obstacles of various kinds and other vehicles has been investigated and in all cases simple mathematical analyses have been found adequate to predict these motions. The obstacles considered were lamp columns, trees, bridge abutments and walls, struck at various angles and speeds, and the two-vehicle collisions covered a range of weights, velocities and collision angles representing head-on, rear-end and intersection accidents. The movements of the car occupants and their velocities, relative to the car during the most violent phases of impact, are also calculated. The theoretical conclusions are illustrated by examples taken from actual accidents.

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A method is described for calculating the percentages of fatal, serious, slight and uninjured occupants in collisions; the first calculations being made for drivers in head-on collisions. The starting points are (1) a diagram giving the probabilities of the four injury levels versus velocity change of the vehicle, and (2) a distribution diagram of the percentages of head-on collisions within successive equal intervals of relative velocity at impact. Calculations of these percentages were made for ratios of the masses of the two vehicles of 1.0 to 9.0, and satisfactory agreement was found with results derived from the national accident statistics. The relevance of the theory to the assessment of the value of safety measures and the determination of human tolerance to impact is discussed.

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