Impaired Curve Negotiation in Drivers with Parkinson's Disease.

Parkinson's disease (PD) is a relatively common, disabling progressive neurodegenerative disorder with a prevalence that increases with age (∼0.3% among the general population and 3% among those over the age of 65 years). 1,2 The number of senior drivers is projected to increase 5-fold from 1986 to 2028 in North America,3 potentially increasing the number of drivers with PD. PD produces characteristic motor dysfunction, together with variable impairments in cognition, vision, sleep, autonomic function, and behavior,1,4,5 and increases the risk of dementia.4 Reliable epidemiological data on the risk of traffic accidents among PD patients does not exist;6 however, PD appears to be associated with a decrease in the frequency of driving and an increase in accidents, especially among those with severe motor and cognitive dysfunction,7 and excessive daytime sleepiness.8 Standardized experimental road testing of PD patients show that while there are individuals within the normal range, drivers with PD as a group perform worse on various driving tasks and make more safety errors compared to drivers of similar age without neurological disease.9-12 Using an instrumented vehicle, we observed that, compared to elderly controls drivers with PD had poorer navigational skills13 and visual search abilities,14 and were affected more by audio-verbal distraction.15 Driving simulator experiments show that drivers with PD have poorer vehicle control,16 increased sleepiness and weaving,17 and higher collision rates compared to controls.18,19 Drivers with PD were also shown to have impaired internal cuing20 and degradation of operational aspects of driving during a concurrent task.21 The addition of driving simulation assessment to a clinical screening battery increased the sensitivity and specificity of off-road testing in predicting the pass/fail status of drivers with PD on an official road test.22 Curves, particularly on two-lane rural roads, are recognized as a significant safety issue and are associated with a 34% increase in accident frequency per sharp curve per kilometer.23 Negotiating curves requires that drivers anticipate the curve by adjusting their speed and lane position to accommodate the severity of the curve, which requires more attentional resources than driving on a straight section of road. In addition to explicit attentional cues (e.g., checking the speedometer), speed selection in curves depends on such implicit perceptual cues as edge rate information presented to the peripheral visual field.24 Possible causes for increased accident rates on curves include the inability to meet increased attentional demands due to fatigue or a medical condition, misperceptions of speed and curvature, and failure to maintain proper lateral position on the curve.23 Drivers with PD have impairment in visual perception, processing speed and attention, and executive and motor functions4,5 that can impair their ability to control their vehicle on a curve. In the present study we examined driver vehicle control and driving safety on curves using a high-fidelity driving simulator, which provides optimal stimulus and response control in a challenging but safe environment.25-27 Our goals were (1) to test the hypothesis that drivers with PD will have less vehicle control and more driving safety errors on curves compared to neurologically normal drivers, and (2) to determine the cognitive, visual, and motor predictors of vehicle control on curves in the PD group.