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.