THE effects of ageing on driving related performance

According to one estimate, about 40 percent of the driving population will be over the age of 60 by the year 2020 in the UK and currently, several hundred thousand drivers with dementia hold driving licenses. The number of motor vehicle crashes per unit distance of automobile travel is “U”-shaped, with risk increasing slightly between the ages of 55 and 60, but risk increasing with each successive five-year interval. Some individuals who have mild dementia possess sufficient driving skills to be designated as fit drivers. The most challenging assessment and decision for the physician/licensing authority as regards fitness to drive lies in drivers who are questionably demented or are in a state of very mild dementia. In the absence of a reliable standard protocol, some clinicians make judgment based on selfreporting, which has risks associated with it as lack of insight and judgment are potential common traits of the population experiencing cognitive decline. Seldom is recourse made by health professionals to on-road assessment as a first alternative as it requires a fee and such testing centers are not readily available everywhere. This research addresses this issue of the identification of cognitive tests that can be used to assess an individual’s ability to drive and especially of those individuals that are questionably demented and are the most difficult to identify. A younger and an older group consisting of 56 drivers in total were administered nine different cognitive tests and two drives (Drive-I and Drive-II) on the STISIM driving simulator. The cognitive test ufov3 (involving the identification of a central target and simultaneously the radial localization of a peripheral target embedded in distracter triangles), which is the third subtest of the UFOV (Useful Field of View) test showed the highest discriminating ability in separating “poor-drivers” from “not-poor-drivers”, with 92.86 % of the drivers correctly classified. The next best discriminating ability in decreasing order of strength was that of dichotic listening test, trail making test, rey-copy test and paper folding test. Also, age was found to be an excellent discriminator of “poor-drivers” and “not-poor-drivers” with 91.07 % of the drivers correctly classified. A composite cognitive measure consisting of the sum of all nine cognitive tests was not a better predictor than the ufov3 test alone; overall it was still an excellent discriminator, classifying 89.29 % of drivers correctly. The commonly recommended Clock Drawing test and the Trail Making test did not emerge as significant predictors of driving ability. A general driving skills linear model for prediction purposes was derived that explained 59 % of the variation in a general driving performance index with the ufov3 test, the dichotic listening test and the rey-recall test as significant predictors. Recommendations are made as to how this test should be used to screen potentially at risk drivers.