Abstract
It is suggested that the errors drivers make are an important source of information, both to the researcher and to the system designer, but one which has been virtually ignored by both until recently. These shortcomings have been supported by researchers' failure to develop theoretical accounts of driver error and classifications of errors which serve both practical and theoretical functions. Models of error from other areas are reviewed here and principles are advanced for classifying drivers errors. The use of error as an index of behaviour in driver testing, training and accident classification is discussed.