Impaired traffic sign recognition in drivers with dementia

Abstract

The determination of the safety of a patient with dementia who continues to drive is a difficult task for the physician who cares for geriatric patients. This study used the Traffic Sign Recognition Test (TSRT) discrimination between dementia patients who continue to drive and normal elderly volunteers. Thirty-seven subjects with dementia who continue to drive and 47 normal elderly volunteers were recruited to participate in the study. Each group was tested with the TSRT similar to that used for licensing in the state of Indiana. The difference in total number of signs correctly identified between the two groups was determined using the Wilcoxon Rank Sum Test. The difference between groups of each individual sign recognition was determined using a Chi Square test. The affected group was also tested with a neuropsychological battery (NB) designed to measure skills thought to be needed for driving.

Drivers with dementia correctly identified 5.95 (± 2.17) of the 10 traffic signs used in licensing as compared to the normal elderly volunteers who correctly identified 8.77 (± 1.58) total signs (p < 0.0001). The “Slow Moving Vehicle” sign provided the largest difference between the two groups; demented drivers correctly identified the sign 39 percent of the time, compared with 89 percent in the normal volunteers (X2= 15.333, df= 1, p < 0.005). Only 76 percent of the demented drivers correctly identified a “Stop” sign compared with 98 percent of the normal elderly drivers. The percentage of correctly identified signs on the TSRT also correlated with several tests in the NB.

Drivers with dementia who continue to drive perform worse on traffic sign recognition than normal elderly drivers. While our current screening tool did not assess the driving safety of either group, it suggests that demented patients who still drive may not recognize common traffic signs and may thus pose a risk to society.