The role of car size and aggressivity in relative collision safety.

There is concern about car size and safety, particularly the roles of crush aggressivity and size in relative safety. Recent research by BASt has shown, when two small cars collide in a frontal accident that the injury risk is twice the risk when two large cars collide. This paper treats the frontal crush behaviour of cars as energy absorbers and shows that the Specific Energy Absorption Capacity of the car population can be regarded as being independent of car mass and length. This implies that the mean collision deceleration is inversely proportional to car length. The crush model is extended to impact between cars of different sizes and is compared first with BASt data for collisions between cars of different masses and high correlation obtained, and secondly with Folksam Insurance data for the relative safety of 47 individual cars where linear correlation is obtained. The model is then used to evaluate the influence of the stiffness of car fronts, soft, average, hard and of the variation of car mass within each size class on relative safety.