Visual attention outperforms visual-perceptual parameters required by law as an indicator of on-road driving performance

PURPOSE: A variety of visual and psychometric tests have been developed for assessing on-road driving performance and fitness to drive. The diagnostic power of a state of the art psychometric test battery (Vienna Test System) combined with a set of standard visual parameters recommended for assessing fitness to drive is investigated using an on-road driving test. The study aimed to determine whether a psychometric test battery could predict older adults’ on-road driving performance. The relevance of visual standards required by law is discussed. METHODS: Vision impairment is more prevalent in later adulthood and many studies on visual and cognitive impact on driving safety and performance therefore focus on adults above 60 years of age. We therefore acquired an extensive set of driving-related visual and psychometric performance parameters in a group of elderly drivers (N = 84, median age 69, SD 6.6 years). Visual assessment included foveal acuity, perimetric field size, and dynamic aspects of peripheral vision (termed “PP”) in the computer-based Vienna Test System (VTS; Schuhfried), as well as letter contrast thresholds in foveal and parafoveal vision in a separate setup. A selection of psychometric driving-aptitude tests that demonstrated the battery’s capacity to predict aspects of driving performance and safety were further conducted on the VTS. Driving performance was assessed in a standardized on-road driving test. Two independent observers rated driving performance using a fixed scoring system assessing the number of driving errors in pre-defined traffic situations. In addition, globalized driving competence scores were assigned on a 6-point scale. RESULTS: The test battery performed excellent in identification of good drivers but failed in the prediction of bad driving performance. Visual performance indicators required by German law were less indicative of driving ability than psychometric assessment. Selective and divided attention turned out to be much more important for predicting fitness to drive than either visual acuity, size of the visual field, or contrast sensitivity. CONCLUSION: Predicting fitness to drive by means of visual and psychometric tests is an ambitious challenge. On the one hand sensitivity of a multi-disciplinary test-battery is too low to predict reliable driving ability in diagnostic settings which require an unambiguous interpretation of test results for individual drivers. Low sensitivity and low predictive values are incompatible with that objective. On the other hand, the results are valuable for a routine screening of fitness to drive. For that case, the assessment of attentional abilities in particular appears to be promising. Performance measures of divided and selective attention showed themselves to be the most predictive for fitness to drive in a sample pre-screened for clear visual deficits. Visual performance parameters required by law, in contrast, had no meaningful impact on driving performance, indicating a gap between mandatory regulations of state authorities and research results. Our results suggest that visual acuity tests designed for clinical diagnosis and monitoring of eye diseases should not at all be the choice for a screening of fitness to drive.