Road safety in drivers with Parkinson disease.

OBJECTIVE: To assess road safety and its predictors in drivers with Parkinson disease (PD). METHODS: Licensed, active drivers with PD (n = 84; age = 67.3 +/- 7.8, median Hoehn & Yahr stage II) and controls (n = 182; age = 67.6 +/- 7.5) underwent cognitive, visual, and motor tests, and drove a standardized route in urban and rural settings in an instrumented vehicle. Safety errors were judged and documented by a driving expert based on video data review. RESULTS: Drivers with PD committed more total safety errors compared to controls (41.6 +/- 14.6 vs 32.9 +/- 12.3, p < 0.0001); 77.4% of drivers with PD committed more errors than the median total error count of the controls (medians: PD = 39.5, controls = 31.0). Lane violations were the most common error category in both groups. Group differences in some error categories became insignificant after results were adjusted for demographics and familiarity with the local driving environment. The PD group performed worse on tests of motor, cognitive, and visual abilities. Within the PD group, older age and worse performances on tests of visual acuity, contrast sensitivity, attention, visuospatial abilities, visual memory, and general cognition predicted error counts. Measures of visual processing speed and attention and far visual acuity were jointly predictive of error counts in a multivariate model. CONCLUSIONS: Overall, drivers with Parkinson disease (PD) had poorer road safety compared to controls, but there was considerable variability among the drivers with PD, and some performed normally. Familiarity with the driving environment was a mitigating factor against unsafe driving in PD. Impairments in visual perception and cognition were associated with road safety errors in drivers with PD.

Driving under low-contrast visibility conditions in Parkinson disease.

OBJECTIVE: To assess driving performance in Parkinson disease (PD) under low-contrast visibility conditions. METHODS: Licensed, active drivers with mild to moderate PD (n = 67, aged 66.2 +/- 9.0 years, median Hoehn-Yahr stage = 2) and controls (n = 51, aged 64.0 +/- 7.2 years) drove in a driving simulator under high- (clear sky) and low-contrast visibility (fog) conditions, leading up to an intersection where an incurring vehicle posed a crash risk in fog. RESULTS: Drivers with PD had higher SD of lateral position (SDLP) and lane violation counts (LVC) than controls during fog (p < 0.001). Transition from high- to low-contrast visibility condition increased SDLP and LVC more in PD than in controls (p < 0.01). A larger proportion of drivers with PD crashed at the intersection in fog (76.1% vs 37.3%, p < 0.0001). The time to first reaction in response to incursion was longer in drivers with PD compared with controls (median 2.5 vs 2.0 seconds, p < 0.0001). Within the PD group, the strongest predictors of poor driving outcomes under low-contrast visibility conditions were worse scores on measures of visual processing speed and attention, motion perception, contrast sensitivity, visuospatial construction, motor speed, and activities of daily living score. CONCLUSIONS: During driving simulation under low-contrast visibility conditions, drivers with Parkinson disease (PD) had poorer vehicle control and were at higher risk for crashes, which were primarily predicted by decreased visual perception and cognition; motor dysfunction also contributed. Our results suggest that drivers with PD may be at risk for unsafe driving in low-contrast visibility conditions such as during fog or twilight.

Predictors of driving safety in early Alzheimer disease.

OBJECTIVE: To measure the association of cognition, visual perception, and motor function with driving safety in Alzheimer disease (AD). METHODS: Forty drivers with probable early AD (mean Mini-Mental State Examination score 26.5) and 115 elderly drivers without neurologic disease underwent a battery of cognitive, visual, and motor tests, and drove a standardized 35-mile route in urban and rural settings in an instrumented vehicle. A composite cognitive score (COGSTAT) was calculated for each subject based on eight neuropsychological tests. Driving safety errors were noted and classified by a driving expert based on video review. RESULTS: Drivers with AD committed an average of 42.0 safety errors/drive (SD = 12.8), compared to an average of 33.2 (SD = 12.2) for drivers without AD (p < 0.0001); the most common errors were lane violations. Increased age was predictive of errors, with a mean of 2.3 more errors per drive observed for each 5-year age increment. After adjustment for age and gender, COGSTAT was a significant predictor of safety errors in subjects with AD, with a 4.1 increase in safety errors observed for a 1 SD decrease in cognitive function. Significant increases in safety errors were also found in subjects with AD with poorer scores on Benton Visual Retention Test, Complex Figure Test-Copy, Trail Making Subtest-A, and the Functional Reach Test. CONCLUSION: Drivers with Alzheimer disease (AD) exhibit a range of performance on tests of cognition, vision, and motor skills. Since these tests provide additional predictive value of driving performance beyond diagnosis alone, clinicians may use these tests to help predict whether a patient with AD can safely operate a motor vehicle.