Predicting road test performance in drivers with dementia

Objectives: To develop a cognitive and functional screening battery for the on-road performance of older drivers with dementia.

Design: Prospective observational study.

Setting: On-road driving evaluation clinic at an academic rehabilitation center.

Participants: Ninety-nine older people with dementia (63% male, mean age 74.2 ± 9), referred by community physicians to an occupational therapy driving clinic.

Measurements: The outcome variable was pass or fail on the modified Washington University Road Test. Predictor measures were tests of visual, motor, and cognitive functioning, selected for their empirical or conceptual relationship to the complex task of driving safely.

Results: Sixty-five (65%) participants failed the on-road driving test. The best predictive model, with an overall accuracy of up to 85% when participants were blinded, included the Eight-item Informant Interview to Differentiate Aging and Dementia, Clock Drawing Test score, and time to complete the Snellgrove Maze Test or Trail Making Test Part A. Visual and motor functioning were not associated with road test failure.

Conclusion: A screening battery that could be performed in less than 10 minutes predicted with good accuracy failure rate for the on-road driving test in this sample of older drivers with dementia. A probability of failure calculator is provided from a logistic regression model that may be useful for clinicians in their decision to refer impaired older adults for further testing. More studies are needed in larger community-based samples, along with discussions with patients, families, and clinicians, with regard to acceptable levels of test uncertainty.