SELECTION OF MODEL STRUCTURE FOR ROAD ACCIDENT SEVERITY

The presence of rare events in the accident data and transferability o f error from one severity level to the other are just two of the issue s in modelling accident severity. This paper explores the implications of different model structures and evaluation criteria using a common data set. Evaluation criteria are statistical fit of submodels, stabil ity and validity of risk factors, overall model prediction, and case-s pecific model predictions. Model structures considered were the sequen ce of injury severity in the model structure, sequential versus nonseq uential models, degree of aggregation, and case control approach. The study concluded that all the different models produce similar results. There is no indication of transferability of error between submodels in the sequential model. It was concluded that a disaggregate model is preferred to an aggregate model given the similarity of results.