The need for, and use of, classified accident types in safety investigations

The report argues that objective information should be collected in accidents rather than subjective information. Specific countermeasures usually affect specific accident types, the accident type and frequency method should be used instead of the individual inquest method. The general accident reporting and recording situation is discussed and specific examples are given of the effects of different systems on aggregated and disaggregated accident data related to particular countermeasures. It is considered that the accidents being studied should be disaggregated into accident types to determine the real effects of a countermeasure. Accident types can be costed according to the average number of casualties and vehicles damaged. If this is done benefit cost studies are meaningful since the analysis will be sensitive to the change wrought by the countermeasure. The number and severities of the casualties within an accident type should be used for costing accidents, not the severity level of the accident, as the number and severity varies according to the accident type (a).