Skills and accident involvement

The concept of accident proneness has been in vogue from the 1920s up until the 1960s, and played an important role in theories of driver behaviour. McKenna (1983) presented a conceptual analysis of accident proneness. The idea was that some individuals are more liable to be involved in accidents than others. The statistical techniques that have been applied to resolve this issue have given rise to substantial controversy. One of the problems mentioned by McKenna is that differential accident liability can always be attributed to differences in exposure to risk. Moreover, the lack of a clear definition of accident proneness has resulted in confusion. Several meanings have been assigned to the concept of accident proneness. Some have understood it as that most accidents are caused by a few people. This is associated with the definition of accident proneness as a disproportionate involvement in accidents in a statistical sense. However, the mere randomness of accidents suggests that some people have been involved in more accidents than others because of ‘bad luck’. Others have regarded it as an individual property, or as a personality characteristic or disposition leading to a disproportional accident involvement. In that case accident proneness is a trait. However, the connection between these (personality) characteristics and actual car driving behaviour resulting in a higher accident involvement is unclear.
McKenna (1982) proposed the differential accident involvement approach as an alternative to the concept of accident proneness because this would offer a better theoretical understanding of the psychological abilities and characteristics associated with human error. Further advantages of this approach are that it does not suffer from the moral and emotional connotations associated with accident proneness, and that it is based on psychological testing instead of statistical modeling. The differential accident involvement approach evaluates the contribution of psychological abilities instead of personality factors to accident involvement. Although this approach has become known as an important representative of the so-called skill model, it is important to note that it is not driving skill as such that is being evaluated but psychological abilities that are assumed to be related to driving skills. Efforts were made to identify the psychological abilities critical to safe car driving. A substantial amount of research was devoted to the study of correlations between performance on perceptual-motor tasks that were assumed to measure abilities required for safe driving on the one hand and accidents on the other hand. Unfortunately, because this approach is purely correlational, the nature of the relation between psychological abilities and accident involvement is not made explicit at all. The existence of such a relation is assumed on intuitive grounds and based on face validity. Because the process controlling this assumed relation was not investigated, the effects of psychological abilities on operational driving performance and on behaviour on the tactical level have not been examined. Therefore, accident involvement has been the only dependent variable in this line of research. The results were generally disappointing. A small overview of some of the extensive relevant literature gives the following results:
Vision is generally accepted as being of central importance in driving. Yet correlations between several visual performance tests such as static acuity, dynamic acuity, visual field, glare recovery and recognition on the one hand and accident rate on the other, are typically lower than 0.05(Rumar, 1988).
The psychological test that has probably been studied most often in relation to accident involvement is the embedded figures test (EFT) of Witkin. This test measures the cognitive style of ‘field independence’ and it requires that a simple form is found within a background. The EFT has been presented as predicting accident rate. Mihal and Barrett (1976) reported a correlation of 0.24 between EFT performance and accident involvement.Loo (1978) obtained a correlation of 0.42 with self-reported accident rate. However,Harano (1970) found a correlation of only 0.001 and McKenna et al. (1986) found a non-significant correlation of 0.19 between EFT performance and accident rate. Also, Quimby and Watts (1981) failed to obtain a significant correlation with accident involvement.
Other psychological tests, such as the dichotic listening test, Stroop test and reaction time tests also have been reported to be poorly related to accident involvement (McKenna et al., 1986; Quimby and Watts, 1981).
Noordzij (1990) reviewed the German literature on individual differences and accident liability. Performance measures on a wide range of tests failed to predict safe driving in any of the reviewed studies. Some studies even reported relations contrary to the expected direction, such that better performance in the laboratory and on the road was associated with poorer accident histories.

McKenna et al. (1986) gave two explanations for the low correlations. The reliability of accident scores is low when these are obtained over only a few years. This makes it impossible to obtain high correlations between accident rate and test performance. Furthermore, accident rate probably reflects different psychological abilities that cannot be captured in a limited number of tests. Häkkinen (1979) demonstrated that the reliability of accident scores increases by lengthening the time over which accidents are measured. He argued that the lack of significant relations between test scores and accident involvement in so many studies was caused by short exposure periods and poor control of environmental risk. Häkkinen studied accident involvement of professional bus and streetcar drivers and found significant differences between safe drivers and accident involved drivers on a number of psychological tests measuring, for example, eye-hand coordination, choice reaction time and psychomotor personality factors. The correlations were over 0.40. The study of Häkkinen has often been referred to a evidence for the skill model, and it is one of the few studies that supports the model.
In summary, psychological abilities assumed to be related to driving skills have proven to be unrelated to accident involvement, except perhaps for professional drivers. Summala (1985) explained the results of Häkkinens’ study by the forced-paced nature of the driving task for this group of drivers. The task of professional bus drivers is paced by time-schedules and differs from the task of private drivers who are able to decrease the speed, overtake less often or avoid bad conditions. The explanation could be that the driver adapts behaviour on the tactical level to the level of operational performance if the driving task is self-paced. This prevents a higher accident involvement for drivers with poorer psycho-motor abilities. This ofcourse assumes that drivers with poorer psycho-motor abilities are characterized by poorer operational performance. However, when the task is forced-paced adaptation is not possible. Unfortunately, the effects of psycho-motor abilities on operational performance and on tactical behaviour, such as speed choice, have not been studied, thus making it impossible to prove the existence of such an adaptive mechanism from the data presented so far. There is however evidence that adaptive processes play an important role in accident causation of elderly drivers, who suffer from age-related performance decrements and in some transient state-related performance decrements. In that case the term compensation is applied instead of adaptation. A research driving simulator is an excellent research tool to investigate these issues further.

The following literature was referred to:

  • Häkkinen, S. (1979). Traffic accidents and professional driver characteristics: a follow-up study. Accident Analysis & Prevention, 11, 7-18.
  • Harano, R.M. (1970). Relationships of field dependence and motor vehicle accident involvement.Perceptual and Motor Skills, 31, 272-256.
  • Loo, R. (1978). Individual differences and the perception of traffic signs. Human Factors, 20, 65-74.
  • McKenna, F.P. (1982). The human factor in driving accidents. An overview of approaches and problems.Ergonomics, 25, 867-877.
  • McKenna, F.P. (1983). Accident pronesness: a conceptual analysis. Accident Analysis & Prevention, 15, 65-71.
  • McKenna, F.P.; Duncan, J. and Brown, I.D.. (1986). Cognitive abilities and safety on the road: a re-examination of individual differences in dichotic listening and search for embedded figures. Ergonomics, 29, 649-663.
  • Mihal, W.L. and Barrett, G.V. (1976). Individual differences in perceptual information processing and their relation to automobile accident involvement. Journal of Applied Psychology, 61, 229-233.
  • Noordzij, P. (1990). Individual differences and accident liability: a review of the German literature. TRRL Contractor Report, 195, Crowthorne.
  • Quimby, A.R. and Watts, G.R. (1981). Human Factors and driving performance. TRRL Laboratory Report 1004, Crowthorne.
  • Rumar, K. (1988). Collective risk but individual safety. Ergonomics, 31, 507-518.
  • Summala, H. (1985). Modeling driver behaviour: A pessimistic prediction? In: EVans L. and Schwing, R.C. (eds.). Human behaviour and traffic safety. Plenum Press, New York, 43-61.

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