Dementia and driving: The current situation

After the age of 70 the accident liability of drivers increases dramatically with distance driven. It has been suggested, however, that the effects of age per se are unlikely to be of sufficient magnitude to account for many accidents and, given that driving can be a complex and cognitively demanding task, cognitively impaired subsets of the older driver population may be disproportionately accounting for large numbers in the accident statistics. In recent years, attention has been given to the role dementia may play in the accident liability of older drivers. Dementia is an age-related medical condition that results in a general impairment of intellect and memory. Cognitive impairments associated with dementia can include difficulty in recall, disorientation, lack of insight and judgment, and disorders of attention. Such impairments typically lead to changes in behavior and personality, and may affect driving. Although it is not known what proportion of older drivers have dementia, it is known that older drivers represent the most rapidly growing segment of the driver population, both in terms of the total number of drivers on the road and the number of miles driven annually per driver. Given the relatively high prevalence rates of dementia among older people, this suggests that increased numbers of cognitively impaired drivers will be on the road in the future. There may therefore be a need to conduct some kind of standard screening procedure to ensure the fitness to drive of older drivers or, alternatively, to introduce standard assessment procedures for people suspected of having a dementing illness. These procedures could not only identify who should have their driving license revoked, but could also be used to help people to continue driving. However, before such procedures can be put in place, it will be necessary to demonstrate both their reliability and validity. From a policy point of view, the safety benefits of introducing such procedures would also need to be weighed against the resultant reductions in mobility. This paper summarizes the findings from a literature review carried out by the Transport Research Laboratory into dementia and driving. The aim of this review was to find out whether drivers with dementia represent an increased risk while driving on the road, what the behavioral manifestations of this increased risk are, and whether screening tests of cognitive function and driving performance can identify those drivers who are at risk so that remedial action can be taken. Evidence shows that drivers with more severe dementia represent a greater risk while driving than do drivers with mild dementia or older healthy controls. However, evidence for an increased risk among drivers with mild dementia is not convincing. Research is fraught with methodological deficiencies such as small sample sizes, poor control groups, and a lack of consideration of important variables including driving exposure and appropriate measures of dementia severity. These problems affect reliability and validity, and may account for inconclusive research findings. There are also problems of reliability and validity concerning research into screening procedures, especially with regard to the outcome measure that should be used to establish their predictive validity. Such issues along with policy implications and recommendations for further research are discussed