Young Driver Research Program - The influence of age-related and experience-related factors on reported driving behaviour and crashes

Federal Office of Road Safety - Contract Report 143

Abstract:

This study investigated the relative importance of youth and lack of driving experience as contributors to the over-representation of young drivers in traffic crashes. Interviews were conducted with drivers aged 16-29 to collect information on their personal characteristics, travel patterns and crash histories. After allowing for differences in exposure (time spent driving), crash involvement was found to be associated with lack of driving experience and with high levels of recklessness. Recklessness was higher amongst younger drivers. Drivers who obtain a licence relatively early were no more reckless than those who are licensed when somewhat older. Young males were significantly more reckless than young females but did not have higher crash risk (after controlling for exposure). Thus, skill levels may be higher among young males, compensating for their greater recklessness. Although experience was found to be more important than age in determining crash risk, the high correlation between the two means that the issue cannot be resolved beyond all doubt. Future research should directly address the skill and motivational variables relevant to crash risk, rather than relying on experience and age as proxies. The present study has taken an important step in this direction by demonstrating that recklessness is a better predictor of young driver crash involvement than age. The report concludes with recommendations for countermeasure development.

Executive Summary

The young driver problem - age or experience?

It has been widely confirmed that young drivers have a greater risk than other drivers of being involved in a traffic crash. The elevated crash risk of young drivers results not from greater distances driven (and thus greater exposure to risk) than other age groups, but from greater risk per unit exposure. A variety of factors may contribute to this high risk level, the most obvious of which is lack of driving experience, since driving skill, like most other skills, is probably acquired largely through practice. Research in Victoria has shown that the rate of casualty crash involvement per distance driven decreases steadily with increasing driving experience. However, experience is not the only correlate of age which may influence crash risk; other factors may be responsible, at least in part, for the decrease in crash rates with increasing age and experience. For example, it has been argued that young people around minimum licensing age are at a stage of life where they reject parental values, strive for independence, experiment with roles and become heavily influenced by their peer group and its values. Thus young people may be motivated to drive fast or take other risks in order to test their own abilities, to demonstrate independence from authority or to impress their peers.

Although driver age and experience are highly correlated, it has been seen as important to determine which is the better predictor of crash risk. The consequences for countermeasure design could be profound. A finding in favour of experience would strongly suggest that the young driver problem is primarily a result of skill deficits, which are gradually overcome with increasing experience of driving. In this case, further research and countermeasure development should concentrate on accelerating the development of those skills which are critical to safe driving. On the other hand, if age is the main predictor of crash risk, countermeasures should focus on age-related motivational and lifestyle factors.

Review of previous studies

There have been several major investigations into the "age versus experience" question during the last three decades. However, previous research in the area was found to be fraught with conceptual and methodological difficulties. Many of the studies reviewed had employed inadequate measures of driving experience, making it difficult to identify a relationship between experience and crash involvement. Such problems did not occur with age, however, which drivers are able to report much more accurately than their driving experience.

Previous studies generally entailed comparisons of the crash involvement of drivers of the same level of experience but different ages, and/or comparisons of drivers of the same age but different levels of experience. In effect, these studies compared drivers who acquired a licence at different ages. All relied on the unstated and untested assumption that differences in the crash risk among such drivers are due entirely to differences in age or experience; drivers who obtain a licence at different ages were assumed to differ in no other respect relevant to crash risk. No systematic attempt has previously been made to identify the factors associated with early licence acquisition and to determine their relevance to crash risk. This shortcoming throws doubt on the conclusions of all studies reviewed. Any tendency for individuals who obtain a licence earliest to have personal characteristics associated with elevated crash risk (independent of age and experience) would contribute to elevation of crash rates among first year drivers at the lowest ages, creating an exaggerated age effect and biasing "age versus experience" comparisons towards a finding in favour of age. Conversely, any tendency for comparatively safe drivers to acquire a licence earliest would bias such studies towards a conclusion that experience is the dominant influence on crash involvement.

Information sources used in the study

Data from driver interviews conducted for a related investigation (also part of the Federal Office of Road Safety's "Young Driver Research Program") were used to examine the factors associated with early and late acquisition of a driver's licence in Australia. The interviews included a comprehensive selection of items expected to be relevant to crash risk, and information on the driving exposure of the respondents during the week before the survey. Drivers who had driven at least once in the previous month were interviewed at their homes in all six states of Australia. The sample was stratified by age group, sex, state and location type (metropolitan versus country). Interviews were obtained from a total of 1688 drivers in the age range 16-29 years. Further information was available from questionnaires administered to a sample of drivers stopped at Random Breath Testing stations in Melbourne and Adelaide. Questionnaires were completed by 371 drivers in the age range 16-29 years. These questionnaires included a substantial sub-set of the items used in the home interview series. The questionnaire data were used where possible to assess the reliability of results obtained from the analysis of the home interview data.

The above surveys did not include questions on crash involvement. In order to obtain crash data, a sub-set of the drivers who had been interviewed during the earlier home interview survey were re-interviewed by telephone. Some 800 interviews were obtained from drivers aged 16-29 years at the time of the home interview survey. Crash histories obtained during the telephone interviews were combined with the travel and personal characteristics collected in the home interview survey to form a single data set for joint analysis.

Age of licence acquisition

Principal components analysis was used to reduce the very large number of variables derived from the home interview data to a more manageable number of "factors" describing the drivers interviewed. Multiple regression was then used to identify the driver characteristics which made the largest independent contributions to prediction of the age at which a driver reported having obtained a licence. Early acquisition of a licence was associated with:

living in a state with a low licensing age
being young (although this result was at least in part an artefact of the sampling procedure)
being male
high scores on Factor 2 from the principal components analysis, which was interpreted as measuring the extent to which respondents had "settled down" (married with children and a mortgage)
high scores on Factor 3 from the principal components analysis, indicating respondents who lived in rural areas, paid rent or board and did not speak a language other than English at home
having completed some form of post-secondary education (tertiary, technical or trade).

There were some indications that drivers scoring high on Factors 2 and 3 may have tended to have relatively low risk of crash involvement. However, Factor 1 from the principal components analysis, which was interpreted as measuring the respondent's "recklessness" (willingness to take risks in driving and non-driving contexts), was the driver characteristic most strongly expected to indicate high crash risk. This factor was found not to be significantly related to age of licence acquisition.

Driver characteristics associated with crash involvement

Out of 800 respondents who were re-interviewed by telephone, one reported three crashes in the previous three years, 12 reported two crashes, 181 reported one crash, and the remaining 606 respondents reported no crashes. Analyses to identify the driver characteristics most strongly associated with crash involvement data were performed twice: once taking account of differences in quantity of exposure, and once without taking account of exposure.

When differences in quantity of exposure were not taken into account, logistic regression analysis revealed that reported crash involvement in the last three years was associated with:

high recklessness (Factor 1),
driving in a wide variety of conditions in the week before the home interview (Factor 4),
having few years of driving experience, and
being male.

After allowing for differences in exposure (time spent driving), crash involvement was associated with:

having few years of driving experience, and
high recklessness (Factor 1).

In both analyses, age was significantly correlated with crash involvement, but did not significantly improve prediction of crash involvement after driving experience had entered the prediction equation. However, in both analyses, as a result of the high correlation between age and experience, very similar probability values were obtained for these two variables during the logistic regression procedure.

None of the three main characteristics which predicted age of licence acquisition (Factors 2 and 3 and post-secondary education) was found to be significantly associated with reported crash involvement, after allowing for the effects of sex, age and experience.

Conclusions on the role of age, experience and related factors

The issue underlying this part of the Young Driver Research Program was that of "Age" versus "Experience" as determinants of young driver crashes. What, then, are the implications of the finding that the strongest predictors of crash risk were Experience and Recklessness?

Clearly, both skill and motivational factors are important elements in young driver crashes. The primary role of Experience in the regression equations indicates that skill deficits play a major role in crash causation among inexperienced drivers. Recklessness, the other main driver characteristic predicting crash risk, was significantly correlated with age, confirming the additional contribution of age-related motivational factors.

Young males were considerably more likely to report crash involvement than were young females. However, after taking into account the much greater exposure of males, there was no significant difference in the overall crash risk of males and females, supporting the view that the greater crash involvement of young males is largely due to their greater exposure to risk as a result of more time spent driving. Nevertheless, young males were significantly more reckless than young females. This suggests that average skill levels may be higher among young males, compensating for their greater recklessness, and that skill deficits play a relatively greater role in the crashes of young female drivers. Such a conclusion is consistent with evidence from previous research that young females have poorer perceptual, cognitive and vehicle control skills. However, experience predicted the crash risk of both males and females, so skill deficits appear to be a problem for young drivers of both sexes.

The finding that experience is a more important determinant of young driver crash risk than age must be regarded as indicative rather than conclusive because of two unresolved, and to some degree irresolvable, difficulties. These are the high correlation between age and experience, and the possible effect of self-selection of age of licence acquisition on the interpretation of the results of this and similar studies. Moreover, there appears to be little prospect of future studies providing any better resolution of this issue as long as the question is posed in its present form: that is, as long as experience is used as an index for the whole spectrum of driving skills likely to be relevant to crash avoidance, and age is used an index of the relevant motivational factors.

To progress beyond our present level of understanding, it will be necessary for future research to address the relevant skill and motivational variables directly. The present study has taken an important step in this direction by demonstrating that "Recklessness", as constructed from the questionnaire data, is a better predictor of young driver crash involvement than is Age.

Future research and countermeasure development

The present study has found that both experience-related driving skills and age-related motivational factors contribute to the over-representation of young drivers in traffic crashes, with skill deficits appearing to play the major role. As a result, the following recommendations for future research and countermeasure development are made:

There is an urgent need to develop improved driver training programs and methods, to ensure that young and novice drivers are equipped with the skills required for safe driving.

To provide a basis for the development of effective training programs, research is required into:

(1) the nature of driving skills (incorporating perceptual, cognitive and motor components);

(2) the basic perceptual and cognitive capacities required to allow the development of these skills (these may differ somewhat for males and females); and

(3) the processes and stages by which young drivers develop these skills.

This research, focussed on driving itself should be supplemented by concurrent research to investigate relationships between particular components of driving skill and particular types of crash.

Graduated licensing schemes should be structured so as to emphasise to young drivers that there are more advanced aspects of driving skill than simple vehicle control. At the end of the prescribed probationary period, drivers should face a valid test of the "higher level" (perceptual and cognitive) components of driving skill The driver should remain on a probationary or provisional licence indefinitely until he or she develops the proficiency required to pass the test.

Research is needed to investigate the ways in which driver attitudes associated with elevated crash risk interact with other variables in their effect on young driver behaviour, particularly behaviour associated with the types of crash in which young drivers are most over-represented.