The British index for comparing the accident record of car models

This paper describes the second part of a study of the ways in which the accident records of different models of car can be compared on the basis of suitably detailed national accident data. An earlier paper (Broughton 1995) showed, from theoretical considerations, that the most satisfactory safety index is the one currently used by the British Department of Transport (DoT) to measure the level of secondary safety (crashworthiness). This paper presents empirical tests using British accident data from 1989-92 which confirm its value. It also describes a modelling approach which yields the same index and thus provides a theoretical justification for the DoT index. The index declines linearly with mass of model; a second safety index is developed on the basis of this relation which allows models of widely differing masses to be compared directly.